Ferroelectric Materials for Energy Applications E-Book

• Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 765

Veröffentlichungsjahr: 2018

Beschreibung

Provides a comprehensive overview of the emerging applications of ferroelectric materials in energy harvesting and storage

Conventional ferroelectric materials are normally used in sensors and actuators, memory devices, and field effect transistors, etc. Recent progress in this area showed that ferroelectric materials can harvest energy from multiple sources including mechanical energy, thermal fluctuations, and light. This book gives a complete summary of the novel energy-related applications of ferroelectric materials?and reviews both the recent advances as well as the future perspectives in this field.

Beginning with the fundamentals of ferroelectric materials, Ferroelectric Materials for Energy Applications offers in-depth chapter coverage of: piezoelectric energy generation; ferroelectric photovoltaics; organic-inorganic hybrid perovskites for solar energy conversion; ferroelectric ceramics and thin films in electric energy storage; ferroelectric polymer composites in electric energy storage; pyroelectric energy harvesting; ferroelectrics in electrocaloric cooling; ferroelectric in photocatalysis; and first-principles calculations on ferroelectrics for energy applications.

-Covers a highly application-oriented subject with great potential for energy conversion and storage applications.
-Focused toward a large, interdisciplinary group consisting of material scientists, solid state physicists, engineering scientists, and industrial researchers
-Edited by the "father of integrated ferroelectrics"

Ferroelectric Materials for Energy Applications is an excellent book for researchers working on ferroelectric materials and energy materials, as well as engineers looking to broaden their view of the field.

Leseprobe

Table of Contents

Cover

Preface

Chapter 1: Fundamentals of Ferroelectric Materials

1.1 Introduction

1.2 Piezoelectric Mechanical Energy Harvesting

1.3 Pyroelectric Thermal Energy Harvesting

1.4 Electrocaloric (EC) Effect of Ferroelectric Materials

1.5 Ferroelectric Photovoltaic Solar Energy Harvesting

1.6 Concluding Remarks

References

Chapter 2: Piezoelectric Energy Generation

2.1 Kinetic Energy Harvesting

2.2 Piezoelectric Vibration Harvesting

2.3 Choice of Materials for Energy Harvesting

2.4 Design and Configuration of Piezoelectric Harvester

2.5 Review of Piezoelectric Thin Films on Metal Substrate (Foils)

2.6 Conclusions

References

Chapter 3: Ferroelectric Photovoltaics

3.1 Introduction

3.2 Historical Background

3.3 Modulation of the Effect

3.4 Summary and Outlook

References

Chapter 4: Organic–Inorganic Hybrid Perovskites for Solar Energy Conversion

4.1 Introduction

4.2 Fundamental Properties of Hybrid Perovskites

4.3 Synthesis of Hybrid Perovskite Crystals

4.4 Deposition Methods of Perovskite Films

4.5 Efficiency Roadmap of Perovskite Solar Cells

4.6 Working Mechanism and Device Architectures of Perovskite Solar Cells

4.7 Key Challenges of Perovskite Solar Cells

4.8 Summary and Perspectives

References

Chapter 5: Dielectric Ceramics and Films for Electrical Energy Storage

5.1 Introduction

5.2 Principles of Dielectric Capacitors for Electrical Energy Storage

5.3 The Energy‐Storage Performance in Paraelectric‐Like Metal Oxides

5.4 The Energy‐Storage Performance in Antiferroelectrics

5.5 Energy‐Storage Performance in Glass‐Ceramic Ferroelectrics

5.6 Energy‐Storage Performance in Relaxor Ferroelectrics

5.7 The General Future Prospects

References

Chapter 6: Ferroelectric Polymer Materials for Electric Energy Storage

6.1 Introduction

6.2 Energy Storage Theory

6.3 Energy Storage of Ferroelectric Polymers

6.4 Energy Storage of Ferroelectric Polymer‐Based Nanocomposites

6.5 Summary

References

Chapter 7: Pyroelectric Energy Harvesting: Materials and Applications

7.1 Introduction to Pyroelectric Energy Harvesting

7.2 Nanostructured and Microscale Materials and Devices

7.3 Hybrid Pyroelectric Generators

7.4 Pyroelectric Oscillator Systems

7.5 Pyroelectric Coupling with Electrochemical Systems

7.6 Porous Pyroelectric Materials

7.7 Figures of Merit and Applications Concerned with Radiations

7.8 Conclusions

Acknowledgments

References

Chapter 8: Ferroelectrics in Electrocaloric Cooling

8.1 Fundamentals of Electrocaloric Effects

8.2 Electrocaloric Devices

8.3 Electrocaloric Materials

8.4 Summary and Outlook

References

Chapter 9: Ferroelectrics in Photocatalysis

9.1 Introduction

9.2 Fundamental Principles of Semiconductor Photocatalysis

9.3 Advances in Understanding Ferroelectric Photocatalytic Mechanisms

9.4 Photochemistry of Ferroelectric Materials

9.5 Photocatalytic Degradation Using Ferroelectric Materials

9.6 Photocatalytic Water‐splitting Using Ferroelectric Materials

9.7 Conclusion and Perspectives

Acknowledgments

References

Chapter 10: First‐Principles Calculations on Ferroelectrics for Energy Applications

10.1 Introduction

10.2 Methods

10.3 Energy Conversion

10.4 Energy Storage

References

Chapter 11: Future Perspectives

11.1 Enhanced Lithium Ion Transport in Polymer Electrolyte

11.2 Enhanced Polysulfide Trapping in Li–S Batteries

11.3 Enhanced Dissociation of Excitons

11.4 New Materials

11.5 New Applications

References

Index

End User License Agreement

List of Tables

Chapter 02

Table 2.1 Acceleration amplitude and frequency of ambient vibration sources from commercial devices.

Table 2.2 Comparison of reported electromagnetic energy harvesters.

Table 2.3 Comparison of three types of transducers for vibration energy harvesting.

Chapter 03

Table 3.1 Band gap values of Si and some of the well‐known ferroelectric materials.

Chapter 04

Table 4.1 Summary of the device information corresponding to efficiencies shown in Figure 4.3. (mp = mesoporous).

Table 4.2 The stability test of some representative PSCs.

Chapter 05

Table 5.1 Code system according to EIA RS‐198 for class 2 capacitors.

Table 5.2 The reported energy‐storage performance of NBT‐based bulk ceramics at room temperature.

Table 5.3 The reported energy‐storage performance of Nb‐contained glass‐ceramics.

Table 5.4 The reported energy‐storage performance of

BaTiO

3

‐based relaxor ferroelectrics.

Chapter 07

Table 7.1 Comparison of relevant equations for pyroelectric

p

= d

P

s

/d

T

(C m

−2

K

−1

) and piezoelectric systems

d

ij

= d

P

s

/d

σ

(C N

−1

) and

is dielectric permittivity at constant stress.

A

is area and h is thickness.

Table 7.2 Processing parameters and selected properties of isotropic porous piezoelectric and pyroelectric ceramics.

Table 7.3 Processing parameters and selected properties of anisotropic porous piezo/pyroelectric ceramics.

Table 7.4 Pyroelectric coefficients

p

and FOMs

F

i,

q

and

F

V

of some ferroelectric ceramics [109] suitable for pyroelectric devices that transduce radiation energy into electric energy.

List of Illustrations

Chapter 01

Figure 1.1 Interrelationship among piezoelectric, ferroelectric, pyroelectric, and dielectric materials. Ferroelectric materials have superior pyroelectric, piezoelectric, and dielectric properties than non‐ferroelectric materials.

Figure 1.2 Schematic perovskite structure of

PbTiO

3

, with cubic (C) structure in the paraelectric state (

P

s

 = 0

) and tetragonal (T) structure in the ferroelectric state (

P

s

 ≠ 0

).

Figure 1.3 Schematic diagram of a potential thermodynamic refrigeration cycle based on EC effect that is similar to a Carnot cycle. From the path of (A)–(B) and then (B)–(C), an applied electric field is raised from

E

1

to

E

2

, which induces a polar‐ordered phase. From (A) to (B), the EC effect material experiences an adiabatic temperature change

Δ

T

hc

from

T

c

to

T

h

, and then from (B) to (C) it ejects heat (entropy) to the heat sink at

T

h

while the material entropy is reduced from

S

c

to

S

h

(isothermal entropy change

Δ

S

). From the path of (C) to (D) and then (D) to (A), the applied electric field is reduced from

E

2

to

E

1

and the EC effect material loses polar ordering. Accompanying this, the EC effect material experiences a decrease in temperature from

T

h

to

T

c

from (C) to (D) (adiabatic temperature change) and then absorbs heat (entropy) from the cold load (isothermal entropy change). Because the EC effect materials of interest are insulators, the above electric field (refrigeration) cycle has the potential of very low electric loss, and consequently, the cooling devices based on the EC effect have the potential to reach very high efficiency.

Figure 1.4 (a) Piezoresponse force microscopy (PFM) image of the ordered arrays of 71° domain walls.

Inset:

Corresponding X‐ray rocking curves, along two orthogonal crystal axes. (b) Schematic diagram of the 71° domain wall arrays. The arrows indicate the different components of polarization (in‐plane and out‐of‐plane), as well as the net polarization direction (large arrow) in the samples. Samples are found to have net polarization in the plane of the film. (c) PFM image of the ordered arrays of 109° domain walls. Inset shows the corresponding X‐ray rocking curves, along two orthogonal crystal axes. (d) Schematic diagram of the 109° domain wall arrays.

Chapter 02

Figure 2.1 Model of a linear mass–spring damper system with a mechanical component and inertial frame for a vibration‐based generator.

Figure 2.2 Acceleration as a function of frequency for the top of a microwave oven.

Figure 2.3 Acceleration as a function of time plot evaluated from data using a tri‐axis accelerometer with a sensing unit located on the arm for an entire day.

Figure 2.4 Schematic of the three types of electromechanical generators: (a) electrostatic, (b) electromagnetic, and (c) cantilever piezoelectric.

Figure 2.5 (a) Direct piezoelectric effect: a polarization is generated by an applied stress; (b) the converse piezoelectric effect: physical displacement is caused by the applied electric field.

Figure 2.6 Perovskite structure.

Figure 2.7 Relationship of the output variables

D

and

S

for piezoelectric transducer.

Figure 2.8 Comparison of

e

31,

f

and FoM of piezoelectric films for MEMS energy harvesting with different orientations on various substrates [22–30]. (Data from: left AlN, (

Sc

0.41

Al

0.59

)N ((Sc,Al)N), ZnO, (100)

BiFeO

3

on

SrTiO

3

((100)BFO), epitaxial

Bi

0.5

Na

0.5

TiO

3

‐Bi

0.5

K

0.5

TiO

3

‐BaTiO

3

(BNT‐BKT‐BT), 0.5 mol% Mn‐doped

(K

0.5

Na

0.5

)NbO

3

(Mn‐KNN), (100) 0.65Pb(Mg

0.33

Nb

0.67

)O

3

‐0.35PbTiO

3

((100)PMN‐35PT), random

Pb(Zr

0.52

,Ti

0.48

)O

3

, (Random PZT(52/48)), (100)

Pb(Zr

0.52

,Ti

0.48

)O

3

on Si ((100)PZT(52/48)), gradient‐free (100)

Pb(Zr,Ti)O

3

on Si (gradient‐free PZT), epitaxial (100)

0.67Pb(Mg

0.33

Nb

0.67

)O

3

‐0.33PbTiO

3

on

SrRuO

3

/SrTiO

3

/Si

((100) (100)PMN‐PT, (001)

Pb(Zr

0.52

,Ti

0.48

)O

3

on Ni foil ((001) PZT on Ni). Epitaxial (001)

Pb(Zr

0.52

,Ti

0.48

)O

3

on (100) MgO with 1 mol% Mn (Mn‐PZT(PZ/48)), {001}

Pb(Zr

0.37

,Ti

0.63

)O

3

on

CaF

2

substrate ({001} PZT(37/63))). Redrawn after Fig. 6 from Ref. [35].

Figure 2.9 Thermal expansion of PZT, Si, Cu, and Ni in the temperature range between crystallization temperature of PZT and room temperature for the residual stress calculation [40–42].

Figure 2.10 Illustration of domain structure in the film under (a) tensile stress and (b) compressive stress, in the cases where the stresses are controlled by thermal expansion mismatch.

Figure 2.11 Effect of thermal strain on the dielectric constant (blue diamond [15]: PZT 48/52, red cubic [45]: PZT 52/48) and P–E hysteresis loops in the PZT 52/48 films.

Figure 2.12 Cantilever piezoelectric energy harvesters with proof masses: (a) 31 mode device using top and bottom electrodes (TBEs) and (b) 33 mode device using interdigitated electrodes (IDE).

Figure 2.13 (a) Bimorph configuration in series connection, (b) bimorph configuration in parallel connection, (c) unimorph configuration, and (d) key to figure.

Figure 2.14 Three types of cantilever beams for piezoelectric energy harvesters and strain distribution along the beam.

Figure 2.15 Frequency response of an oscillator with stiffness nonlinearity. (

∣

x

∣

is the steady‐state amplitude,

Ω

is the input excitation frequency,

ω

n

is the resonant frequency of the system, and

δ

is the coefficient of the cubic nonlinearity).

Figure 2.16 Potential as a function of position for a bistable resonator: (a) intrawell oscillations, (b) chaotic interwell vibrations, and (c) interwell oscillation.

Figure 2.17 (a) Bistable cantilever type of resonator using magnetic repulsion and (b) magnetic attraction.

Figure 2.18 Comparison of a number of MEMS piezoelectric energy harvesters. Those shown in open symbols correspond to piezoelectrics on metal foils.

Chapter 03

Figure 3.1 Open circuit voltage measured while varying the wavelength with the light polarization perpendicular (

σ

) and parallel (

π

) to the direction of spontaneous polarization (

P

s

) in the crystal. The dotted lines depict the corresponding absorption coefficients measured in the two geometries.

Figure 3.2 Photovoltaic current measured along the direction of polarization (

J

z

) and along the other two crystal axes (

J

x

and

J

y

). The current was measured as a function of the angle (

β

) which the plane of linearly polarized light makes with the crystal axis [23].

Figure 3.3 Variation of the photocurrent as the sample is rotated with respect to the electric field of the linearly polarized light. The polarization direction of the crystal is indicated as P.

Figure 3.4 Schematic depicting the separation of electron–hole pair generated within a domain wall upon illumination.

Figure 3.5 Current–voltage characteristics measured with a conductive tip as an electrode to collect photo‐generated charge carriers within the area of illumination.

Figure 3.6 Temperature dependence of the open circuit voltage for 109° domain walls in (a) perpendicular and (c) parallel geometry, and for 71° domain walls in (b) perpendicular and (d) parallel geometry.

Figure 3.7 (a) Topography of a 16‐cell device with the state of polarization depicted by blue (up polarization) and red (down polarization) color. (b)

V

oc

measured across each cell.

Figure 3.8 Spectral distribution of photovoltaic current measured with different materials as top electrode and for different orientations (up and down) of polarization.

Figure 3.9 (a) Calculated values of band gap as a function of polarization for different materials in their respective tetragonal and rhombohedral phases. (b) Difference in the band gap between tetragonal and rhombohedral phases as a function of the

B

‐site cation valence.

Figure 3.10 Absorption measured as function of photon energy. The linear extrapolation provides the values for direct optical band gap in

BiFeO

3

thin films grown in relaxed and strained phases. The inset shows the absorption coefficients determined by numerical inversion.

Figure 3.11 (a) Spectral distribution of photoconductive current measured from crystals grown in different batches. Crystals C3 and C5 were synthesized in the group of Viret and Schmid, respectively. (b) Open circuit voltage plotted as a function of the area measured under the peaks positioned around 470–700 nm in (a).

Figure 3.12 Photostriction in SbSI measured by analyzing the behavior of

Δ

L

/

L

with temperature.

Figure 3.13 (a) Time scans measured at the low‐ and high‐angle sides of the (003) reflection of PTO depicting the movement of peak toward lower angles with time. (b) Rocking curves (

ω

‐scans) measured around (003) reflection at the time intervals shown in (a).

Figure 3.14 Photostriction measured in the

BiFeO

3

crystal as a function of time, under illumination of different wavelengths. The inset compares the photostriction measured at different wavelengths and white light for the same duration of time.

Chapter 04

Figure 4.1 Schematic diagram of the crystal structures of organic–inorganic hybrid perovskites.

Figure 4.2 Schematic illustration of the one‐step (a) and two‐step (b) spin‐coating procedures for the fabrication of perovskite films. (c) Dual‐source thermal evaporation system for depositing the perovskite absorbers.

Figure 4.3 Efficiency roadmap for organic–inorganic hybrid PSCs [1, 2, 25, 28, 34, 43, 44, 49, 51, 53, 58, 59].

Figure 4.4 Schematic illustration of the mesoporous, bilayer, n–i–p planar and p–i–n planar device architectures of PSCs.

HTL

represents the

hole transport layer

;

ETL

represents the

electron transport layer

.

Chapter 05

Figure 5.1 (a) The diagram of charge separation in parallel‐plate capacitor under an electric field. (b) The diagram of a multilayer capacitor.

Figure 5.2 Diagram of the charge–discharge process from

P

–

E

measurements.

Figure 5.3 Schematic circuit of the Sawyer–Tower circuit for measuring the

P–E

loops.

Figure 5.4 Diagram of the charge–discharge measurement circuit.

Figure 5.5 The discharged

I

(

t

)

–t

curve under different charged electric fields.

Figure 5.6 The diagram of the polarization process and

P–E

loops of AFEs.

Figure 5.7 (a)

P

–

E

loops and (b) electric field‐dependent recoverable of

PbZrO

3

thin films with different orientation.

Figure 5.8 Electric‐field‐dependent energy‐storage density and energy‐storage efficiency curves of the

Pb

0.97

La

0.02

(Zr

0.98

Ti

0.02

)O

3

thick films measured at room temperature and up to their critical breakdown field. The insert shows their room‐temperature breakdown field.

Figure 5.9 Electric‐field dependence of recoverable energy‐storage density and energy‐storage efficiency of the PLZST AFE thick films with

x

 = 0.05, 0.25, and 0.40. The inset gives the corresponding temperature dependence of the recoverable energy‐storage density measured at

800 kV cm

−1

.

Figure 5.10 (a–c) Room temperature

P

–

E

loops of the PLZST(111), PLZST(110), and PLZST(100) AFE thick films at 1 kHz. (d–f) The corresponding schematic diagram of the primitive cells.

Figure 5.11 Discharged

I–t

curves of the

Pb

0.925

La

0.05

(Zr

0.42

Sn

0.40

Ti

0.18

)O

3

ceramics capacitor after 1, 10, 100, 1000, and 2000 charge–discharge cycling under

3.5 kV mm

−1

.

Figure 5.12 (a)

P

–

E

hysteresis curves and (b) energy‐storage density as a function of the electric field of the 9.2‐nm‐thick

Hf

0.3

Zr

0.7

O

2

capacitor at various temperatures (25–175 °C). (c)

P

–

E

hysteresis curves and (d) energy‐storage density as a function of the electric field of the 9.2‐nm‐thick

Hf

0.3

Zr

0.7

O

2

capacitor after various electric field cycling procedures with a pulse height of

3.26 MV cm

−1

at the cycling frequency of 500 kHz.

Figure 5.13 Schematic diagram of technological processes of the glass‐coated ferroelectric ceramic grain and ceramics.

Figure 5.14 FE‐SEM micrographs of

(Ba,Sr)TiO

3

glass‐ceramics crystallized by conventional sintering (a) and microwave sintering (b).

Figure 5.15 Schematic of charge and discharge mechanism under an electric field in a dielectric capacitor: (a) without interfacial polarization, (b) with low interfacial polarization, and (c) with high interfacial polarization.

Figure 5.16 BDS and activation energy

E

a

as a function of sintering temperature for the glass ceramics.

Figure 5.17 Room temperature phase diagram of PLZT solution.

Figure 5.18 The electric field dependence of energy‐storage density and energy‐storage efficiency of

(Pb

0.91

La

0.09

)

(Zr

0.65

Ti

0.35

)O

3

thin film measured at room temperature and 1 kHz. The inset shows the

P

–

E

loop of the thin film measured at room temperature and at 1 kHz.

Figure 5.19 (a) Electric field‐dependent energy‐storage performance of PLZT films doped with 0, 1, 3, and 5 mol% Mn. (b) Temperature‐dependent energy‐storage performance of composition‐graded PLZT films.

Figure 5.20

P

–

E

loop of a

0.4BiFeO

3

–0.6SrTiO

3

thin film at 1 kHz at room temperature.

Chapter 06

Figure 6.1 The D–E loops of (a) linear dielectrics and (b) ferroelectric dielectrics.

Figure 6.2 The schematic image of (a) all‐trans PVDF chain, (b) P(VDF–CTFE) chain, and (c) P(VDF–HFP) chain.

Figure 6.3 The schematic image of (a) Tanaka's model and (b) Lewis's model.

Figure 6.4 (a) Weibull distribution of breakdown strength and (b) energy density of stretched P(VDF–HFP) and nanocomposite with 5 wt% nanofiller; (c) The D–E loops and (d) the charge–discharge efficiency of nanocomposites with different nanofiller loading [77].

Figure 6.5 (a) SEM image and (b) elements mapping image of

BaTiO

3

@TiO

2

nanowires; (c) energy density and (d) the charge–discharge efficiency of nanocomposites with different nanofiller content [18].

Figure 6.6 Schematic and cross‐sectional SEM images of (a)

BaTiO

3

/P(VDF–CTFE)

nanocomposite with 15 wt% nanofiller and (b) three‐phase nanocomposite with 12 wt% BNNSs and 15 wt% of

BaTiO

3

; (c) D–E loops, (d) energy density, and (e) charge–discharge efficiency of pure P(VDF–CTFE) and three‐phase nanocomposite with 12 wt% BNNSs and 15 wt% of

BaTiO

3

[124].

Chapter 07

Figure 7.1 The pyroelectric effect: (a) poled material and corresponding bound surface charge, (b) applied thermal cycle; (c) heating leads to a decrease in polarization and free surface charge for current generation; (d) cooling leads to increase of polarization leading to current reversal.

P

s

is the spontaneous polarization, and

I

is the currency caused by a change in bound charge.

Figure 7.2 Pyroelectric generator with patterned top electrode exposed to

infrared

(

IR

) radiation, which is reflected at the aluminum electrode but absorbed at the exposed PVDF area.

Figure 7.3 (a) Illustration of photothermally driven pyroelectric and thermoelectric device, (b) temperature of the interface for different electrode samples under NIR exposure, (c) temperature measured for all samples, including samples covered with thermal paste (w/TP), (d) output voltage of the photothermally activated pyroelectric film device under NIR on/off, and (e) output power density and integrated power (blue line) of pyroelectric energy harvester.

Figure 7.4 (a) Schematic illustration of a water‐vapor‐driven nano‐generator. (b) A photograph of an assembled pyroelectric nano‐generator held above a cup of hot coffee.

Chapter 08

Figure 8.1 The correlation diagram between elastic, electrical, and thermal properties in a crystal. The

a

ij

,

d

ijk

, and

p

i

are the thermal expansion, piezoelectric, and pyroelectric coefficients, respectively. The

are the corresponding converse coefficients.

Figure 8.2 Schematic entropy–temperature diagram in an electrocaloric adiabatic process.

Figure 8.3 Schematic configuration of direct ECE measurement setup with heat flux sensor [13, 14].

Figure 8.4 (a) Schematic configuration of direct ECE measurement setup with thermistor. (b) Signal of

Δ

T

sat

versus time.

Figure 8.5 Positive theoretical and experimentally measured adiabatic electrocaloric temperature changes of (a) BaTiO

3

, (b) PbTiO

3

, (c) 0.9Pb(Mg

1/3

Nb

2/3

)O

3

–0.1PbTiO

3

, and (d) 0.65Pb(Mg

1/3

Nb

2/3

)O

3

–0.35PbTiO

3

single crystals.

Figure 8.6 Negative electrocaloric temperature changes in antiferroelectric (Pb

0.97

La

0.02

)(Zr

0.95

Ti

0.05

)O

3

thin films.

Figure 8.7 A mechanism schematic of negative electrocaloric effect in antiferroelectrics. (a)

Δ

E

= 0

, (b)

Δ

E

 ≠ 0

.

Figure 8.8 Diagram of the Stirling cycle in the pyroelectric energy recovery and harvesting. The inset: a simple circuit schematic. The capacitor (

C

) is the ferroelectric element, and the direct current bias field is provided by the battery. Each

C

cycle starts at point 1 and moves around to point 4, and is cycled between two temperatures

T

1

and

T

2

(

T

1

< T

2

).

Figure 8.9 (1) An electric field

E

1

is applied to the EC element, and the heat from the EC materials is released into the fluid and a +Δ

T

is caused in the fluid, heating the fluid. (2) The electric field

E

1

is disconnected, and the fluid is pumped past the EC element so that the excess heat is lost at the heat exchanger

2

. (3) The EC element is shorted so that the field returns to zero and a −Δ

T

is caused in the fluid, cooling the fluid. (4) The EC element is again put to open circuit, and the fluid is pumped back into the heat exchanger

1

, so that the fluid then absorbs heat from the heat exchanger

1

.

Figure 8.10 Conceptual design schematic of ferroelectric thin film with 180 domain structures as solid‐state refrigerators.

Figure 8.11 Front and cross‐sectional views of a multilayer ceramic capacitors.

Figure 8.12 |Δ

T

|/|Δ

E

| and |Δ

S

|/|Δ

E

| (inset) of the Pb[(Ni

1/3

Nb

2/3

)

0.6

Ti

0.4

]O

3

single crystal.

Figure 8.13 Δ

T

of the Pb(Zr

0.95

Ti

0.05

)O

3

thin films.

Figure 8.14 Δ

T

and ΔS (inset) of the PBZ thin films. (a) Around room temperature, and (b) around

T

dp

and

T

c

.

Figure 8.15 (a) Temperature‐dependent polarization–electric field hysteresis, (b) polarization–temperature plot, and (c)

Δ

T

and

Δ

S

of the

Hf

0.5

Zr

0.5

O

2

ferroelectric thin films.

Figure 8.16 (a)

Δ

T

and (b)

Δ

S

of the P(VDF‐TrFE) 55/45 mol% ferroelectric copolymer thin films. Inset in (a): the dielectric permittivity as a function of temperature.

Figure 8.17 Directly measured

Δ

T

(a) and

Δ

S

(b) in the non‐stretched P(VDF‐TrFE‐CFE) 59.2/33.6/7.2 mol% relaxor ferroelectric terpolymer thin films;

Δ

T

(c) and

Δ

S

(d) in the stretched thin films.

Figure 8.18 Indirectly and directly measured

Δ

T

in P(VDF‐TrFE‐CFE) 59.2/33.6/7.2 mol% relaxor ferroelectric terpolymer thin films.

Figure 8.19 The electrocaloric effect for the Δ

T

of the ferroelectric and irradiated P(VDF‐TRFE) copolymers. Δ

T

is measured using a specially designed calorimeter.

Figure 8.20

Δ

T

and

Δ

S

of P(VDF‐TrFE‐CFE)/BNNSs/BST67 ternary polymer nanocomposites at 9 vol.% BNNSs and different BST contents versus P(VDF‐TrFE‐CFE).

Figure 8.21 (a) The BST nanowire array on scotch tape and bended with the tweezers. Inset: cross‐sectional view SEM image. (b)

Δ

T

and |Δ

T

|/|Δ

E

|

of the BST nanowire array as a function of electric field.

Figure 8.22 Schematic of various mesophases for rod‐like liquid crystal molecules for positive ECE: (a) isotropic, (b) nematic, and (c) smectic A phases. (d) 5CB Molecular structure.

Figure 8.23 The electrocaloric effect for

Δ

S

of 5CB liquid crystals in homogeneously aligned cells.

Figure 8.24 Positive and negative electrocaloric cooling cycles in (a) ferroelectrics and (b) fast ion conductors, respectively.

Chapter 09

Figure 9.1 A schematic of the photoinduced generation mechanism for electron–hole pairs in semiconductors with presence of a water pollutant.

Figure 9.2 (a) A schematic illustration of the fundamental mechanism for a semiconducting photocatalytic water‐splitting process. (b) The energy diagrams for photocatalytic water‐splitting.

Figure 9.3 A schematic illustration of the fundamental mechanism for a semiconducting photoelectrochemical water‐splitting process.

Figure 9.4 A schematic diagram of external and internal screening mechanisms by adsorbing charges and free carriers/defects in ferroelectric materials.

Figure 9.5 A schematic diagram of band bending in a ferroelectric material: a surface with negative polarity (a) and a surface with positive polarity (b).

Figure 9.6 Topographic atomic force microscopy (AFM) images of the {001} surfaces of a

BaTiO

3

single crystal: (a) Clean surfaces before the reactions. (b) The same surface area as in (a) after illumination in an aqueous

AgNO

3

solution. The white contrast corresponds to the deposited Ag particles. (c) The same area as in (b) after a cleaning of those Ag particles and then illumination in an aqueous lead acetate solution. The white contrast corresponds to Pb‐containing deposits [36]. (d) The SEM images of faceted

BaTiO

3

crystals after reaction in aqueous

AgNO

3

, where the speckled white contrast corresponds to Ag‐containing deposits. (e) The SEM images of faceted

BaTiO

3

crystals after reaction in aqueous

Pb(C

2

H

3

O

2

)

2

. The white contrast corresponds to oxidized Pb‐containing deposits.

Figure 9.7 AFM images of four

Ba

1−

x

Sr

x

TiO

3

samples with different compositions after reaction and then being covered with silver particles: (a)

x

 = 0.2, the black‐to‐white contrast is 95 nm in height difference; (b)

x

 = 0.26, the black‐to‐white contrast is 60 nm in height difference; (c)

x

= 0.27, the black‐to‐white contrast is 60 nm in height difference; and (d)

x

= 0.4, the black‐to‐white contrast is 110 nm in height difference. All the images have a 20‐μm field of view and a scale mark is shown in (c).

Figure 9.8 Piezoelectric force microscopy (PFM) phase images (a and d) of the PZT/SRO/STO and PZT/LSCO/STO heterostructures respectively. The PFM images indicate that the virgin state in PZT/SRO/STO heterostructure is positively polarized and the virgin state in PZT/LSCO/STO heterostructures is negatively polarized. Scanning electron microscopy (SEM) images (b and e) taken from the surfaces of the PZT/SRO/STO and PZT/LSCO/STO heterostructures. The SEM images obtained after UV irradiation show that the particle density on the surface of PZT/SRO/STO heterostructures is visibly higher. (c) The band structure for a positively polarized PZT thin film, showing the accumulation of electrons underneath the surface, which allows the reduction of Ag ions to occur more readily. (f) The band structure is sloped in the opposite direction for a negatively polarized PZT, causing the electrons to travel inside the film.

Figure 9.9 AFM images after Ag photoinduced deposition on

LiNbO

3

surface using 314 nm illumination for 60 s (a), 100 s (b), and 240 s (c).

Figure 9.10 Schematic band diagrams for

BiFeO

3

where

φ

is the work function,

E

0

,

E

c

,

E

F

, and

E

v

are the energy levels of a free electron, the conduction band edge, the Fermi level, and the valence band edge, respectively. (a) Bands of bulk

BiFeO

3

. (b) Bands of

BiFeO

3

in contact with solution, with the standard redox potential for Ag

+

/Ag versus normal hydrogen electrode. (c) Bands in contact with solution and a positive out‐of‐plane polarization. (d) Bands in contact with solution and a negative out‐of‐plane polarization.

Figure 9.11 Schematic illustrations of domains in the substrate, indicating the promotion of the same half reactions on both the bare substrate (a) and the film surface (b). (c) The AFM images of 15‐nm‐thick (001)‐oriented anatase

TiO

2

film supported by (100)‐oriented

BaTiO

3

after a photochemical reaction in aqueous silver nitrate solution. (d) The AFM images of 15‐nm‐thick (100)‐oriented rutile

TiO

2

surface supported by (111)‐oriented

BaTiO

3

after a photochemical reaction in aqueous silver nitrate solution [55, 56].

Figure 9.12 A clean background on PZT in the negative orientation is “written” by poling a large square area with +10 V (a). The nanostructure pattern inside this square area is produced with a local negative field −10 V (b). Subsequent Ag photo‐deposition results in a pattern of nanoparticles (c). Particle size and spacing can be controlled by deposition time and conditions. Wire‐like structures of aligned nanoparticles are fabricated on the smallest diameter domains (d). Reaction of this structure with dodecanethiol results in attachment of the long chained molecules to the nanoparticles.

Figure 9.13 (a–c) AFM images of periodically poled

LiNbO

3

single crystal surfaces after Ag photo‐deposition at three excitation wavelength bands (3.4, 2.6, 2.3 eV) using the evanescent illumination geometry. (d–f) The zoomed‐in images of (a–c).

Figure 9.14 A schematic drawing of a ferroelectric material showing the effect of free carrier reorganization on band structure and photoexcited carriers (a). Photo‐decolorization profiles of RhB with different catalysts under solar simulator (b). The catalysts consisting of higher tetragonal

BaTiO

3

phase after annealing show higher activity, especially in case of modification by Ag nanoparticles.

Figure 9.15 (a) Photocatalytic activity of

BaTiO

3

nanoparticles at 30 and 80 °C. The inset schematic shows how the internal spontaneous polarization of ferroelectric materials affects photocatalytic reaction. (b) Photocatalytic performance of degradation RhB under UV irradiation.

Figure 9.16 Decolorization curves of (a) RhB and (b) acid black 1 under simulated solar light using

LiNbO

3

,

Fe‐doped LiNbO

3

, and Mg‐doped

LiNbO

3

powder as the catalyst. (c) Proposed mechanism for formation of reactive species on the surface of

LiNbO

3

. Electrons reduce oxygen to form the superoxide anion radical at the C

+

face, and hole carriers oxidize water or hydroxyl ions to form the hydroxyl radical at the C

−

face.

Figure 9.17 (a)

Transmission electron microscopy

(

TEM

) image of heterostructured particles composed of

PbTiO

3

and

TiO

2

. (b) Photocatalytic degradation with different samples during irradiation by visible light (

λ

> 420 nm). Blank refers to data from a control experiment without the addition of a catalyst. The schematic energy level diagrams of

PbTiO

3

–TiO

2

with (c) negative polarization and (d) positive polarization normal to the heterostructural interface.

E

vac

,

E

C

,

E

F

,

E

v

, and

E

s

are the energies of vacuum level, conduction band, Fermi level, valance band, and surface potential, respectively.

Figure 9.18 (a) UV–Visible spectra of pure

BaTiO

3

nanoparticles and

BaTiO

3

/5

 wt% graphene nanocomposites and graphene (insets are images). (b) Visible light photocatalytic degradation of MB by pure

BaTiO

3

, BaTiO

3

/5

 wt% graphene nanocomposites, and no photocatalyst. (c) Photocatalytic degradation of MB under the irradiation of visible light over the

BaTiO

3

–graphene composites with different contents of graphene. (d) A schematic illustration showing the reaction mechanism for the photocatalytic degradation of organic pollutants over the

BaTiO

3

–graphene composites.

Figure 9.19 (a) SEM image of

BiFeO

3

nanoparticles with the TEM image as the inset. (b)

High resolution transmission electron microscopy

(

HRTEM

) image of a nanoparticle with the

selected area electron diffraction

(

SAED

) pattern as the inset. (c) Photocatalysis of

BiFeO

3

nanoparticle samples on degradation of methyl orange under UV–Vis light irradiation and visible light irradiation.

Figure 9.20 (a) The kinetics of RhB degradation using

BiFeO

3

nanoparticles with various additives under visible light irradiation. (b) A schematic illustration of the pollutants degradation mechanism using

BiFeO

3

nanoparticles under visible light irradiation.

Figure 9.21 (a) Photocatalytic degradation efficiencies of RhB using BGFO

x

nanoparticle samples. (b) The changes of temporal UV–Vis spectral of RhB aqueous solution over BGFO (

x

 = 0.1) nanoparticle sample. (c) XRD patterns of the BGFO (

x

 = 0.1) nanoparticles before and after the degradation experiment. (d) UV–Vis diffuse reflectance spectrum of the BGFO (

x

 = 0.1) nanoparticles; the inset shows the calculation of band gap.

Figure 9.22 Photocatalytic degradation efficiencies of RhB using different samples. (b) The relationship between the rate constants and different samples. (c) HRTEM image of the composite heterojunction structure. (d) A schematic illustration for the calculated energy level diagram of

BiFeO

3

/γ‐Fe

2

O

3

.

Figure 9.23 (a) Normalized UV–Vis absorption spectra of

BiFeO

3

nanowires and the

Au/BiFeO

3

nanocomposite dispersed in ethanol. (b) Oxygen evolved upon visible light (

λ

 > 380 nm) illumination of the

FeCl

3

suspension containing different photocatalysts.

Figure 9.24 (a) Illustration of the corona‐poling system. (b) Amount of hydrogen evolution for polarized and non‐polarized

Na

0.5

K

0.5

NbO

3

powder under UV‐light irradiation. (c) Temporal profile of

H

2

evolution for polarized

Na

0.5

K

0.5

NbO

3

powder.

Figure 9.25 Calculated potential distributions and electric poling test of the ferroelectric enhancement. (a) Potential distribution of 150 °C

TiO

2

/5 nm

BaTiO

3

/NaOH

heterojunction, where the spontaneous polarization of

BaTiO

3

shell induces an upward band bending of

TiO

2

core and facilitates the charge separation and transportation inside

TiO

2

. (b) Potential distribution of the 210 °C

TiO

2

/40 nm

BaTiO

3

/NaOH

heterojunctions, showing a strong electric field inside

BaTiO

3

, which facilitates the hole transport toward solution. (c)

J

–

V

curves of the as‐prepared (red), positively poled (blue), and negatively poled (magenta) 150 °C

TiO

2

/BaTiO

3

NWs. (d)

J

–

V

curves of the as‐prepared (red), positively poled (blue), and negatively poled (magenta) 210 °C

TiO

2

/BaTiO

3

NWs.

Figure 9.26 (a) External quantum yield spectra measured for

BiFeO

3

photoelectrodes before poling and after +8 and −8 V poling. (b) Photocurrent–potential characteristics of the photoelectrodes with different polarization states. Schematic representations of the mechanisms in photoexcited charge transfer from

BiFeO

3

films to the electrolyte ➀ and from excited surface modifiers to the

BiFeO

3

films ➁ after the

BiFeO

3

films are (c) positively and (d) negatively poled.

Figure 9.27 Variations of the photocurrent density with applied voltage (V versus Ag/AgCl) under chopped simulated sunlight illumination on

Bi

2

FeCrO

6

/CaRuO

3

/SrTiO

3

sample: (a) before, (b) after negative poling, and (c) after positive poling. Schematic illustrations are shown on the right of each figure.

Figure 9.28 (a, b) EQE spectra and photocurrent–potential measurements of the as‐grown (black), +10 V (red), and −10 V (blue) poled samples. (c, d) Schematic electronic band structure and mechanisms for the injected hot‐electron transfer from

Pb(Zr

0.20

Ti

0.80

)O

3

films to the electrolyte for the two poling configurations [106].

Figure 9.29 (a) Linear sweep voltammograms collected from

BiFeO

3

/ε‐Fe

2

O

3

electrodes with different percentages of

ε‐Fe

2

O

3

in the dark and under light illumination. (b) Photocurrent density histograms for various

BiFeO

3

/ε‐Fe

2

O

3

photoelectrodes. The inset presents the curves of current density versus time at 0.6 V versus Ag/AgCl for all the films. The light is turned on and off at a time interval of 5 min. (c) Linear sweep voltammograms curves of

BiFeO

3

/ε‐Fe

2

O

3

electrodes with different thickness and the curves of current density versus time are shown in the inset (top left), and (d) long‐term stability measurement of the photocurrent density versus time at 0.6 V versus Ag/AgCl for

BiFeO

3

/ε‐Fe

2

O

3

films.

Chapter 10

Figure 10.1 (A) Schematic illustration of the polarization directions. The lowest free energy path is found along the path a–f–g–e. (B) Computed pressure dependence on piezoelectricity in

PbTiO

3

. From the top to the bottom are spontaneous polarization

P

s

, piezoelectric stress coefficients

e

15

and

e

33

, and piezoelectric strain coefficients

d

15

and

d

33

, respectively. (C) Piezoelectric coefficients as a function of temperature in disordered (4

mm

)

Pb(Zr

0.5

Ti

0.5

)O

3

. Solid lines and dashed lines correspond to the cases of including and neglecting of

E

loc

.

Figure 10.2 The temperature dependence of the Cartesian components of (a) the toroidal moment, (b) axial piezotoroidic coefficients, and (c) electric toroidal susceptibility elements, for a cubic nanodot of

PbZr

0.6

Ti

0.4

O

3

(PZT) having 48 Å of lateral size, and being under stress‐free and open‐circuit boundary conditions, as predicted from the first‐principles‐based technique employed here and from the use of Eqs. 10.12 and 10.13. The inset of (c) shows the dipole vortex structure in the nanodot. The theoretical temperature has been rescaled to match the experimental value of the Curie temperature in bulk PZT.

Figure 10.3 (a) The strain state of the (

BaTiO

3

)

10

/(SrTiO

3

)

n

nanowires with

n

= 2, 3, and 4 as a function of temperature at zero external fields. (b) The calculated piezoelectric

and piezotoroidal

coefficients of (

BaTiO

3

)

10

/(SrTiO

3

)

2

and (

BaTiO

3

)

10

/(SrTiO

3

)

3

nanowires. (c) Inverse and (d) direct piezotoroidal effect in (

BaTiO

3

)

10

/(SrTiO

3

)

2

nanowire at

T

= 250 K. The nanowire has an initial purely toroidal state. (c) The strain state of the nanowire as a function of a curled field

E

C

 = 

S

a

e

z

 × 

r

. The insert depicts the strain state of BTO nanodot as a function of

S

a

at

T

= 250 K. (d) The toroidization and polarization as functions of constrained strain

η

33

.

Figure 10.4 Schematic drawing of the coupling between the strain gradient and polarization for perovskite

ABO

3

at the unit cell level: (a) longitudinal, (b) transverse, and (c) shear flexoelectricity. The longitudinal flexoelectric coefficient

f

3333

of rhombohedral

BaTiO

3

for different supercell sizes (

N

 = 6, 10, 14) under various strain gradient,

ε

max

 = (d) 0.5%, (e) 1.0%, (f) 1.5%, (g) 2.0%. In each panel, the squares are for the unrelaxed strain, the dots are for the relaxed strain. The two values converge as the supercell size is increased.

Figure 10.5 The experimental current and computed current of

BaTiO

3

as a function of energy above their respective band gaps, for both transverse (

xxZ

) and longitudinal (

zzZ

) electric field orientation.

Figure 10.6 Projected density of states analysis shows that the electronic structure of (a)

Ba(Ti

0.875

Ce

0.125

O

3

)

differs greatly from (b)

Ba(Ti

0.75

Ce

0.125

Pd

0.125

)O

3 − 

δ

. While Ba (black) does not contribute to the states surrounding

E

gap

, combinations of Ti 3

d

(blue), Pd 4

d

(green), Ce 4

f

(magenta), and O 2

p

(red) states compose the various HOMOs and LUMOs. Values decrease markedly for (c) with the introduction of an O‐vacancy stabilized Pd. (c) Dependence of the total energy on

site of

SrRuO

3

‐BiFeO

3

(BFO) supercell. Number of

n

denotes relative position of the

site with respect to the negatively charged interface

RuO

2

‐FeO

. The (+) and (−) denote the positively and negatively charged interface, respectively. . (d) The calculated optical absorption curves for

BFO/TiO

2

(TO) heterostructures under different compressive and tensile strains, as well as the BFO and TO films.

Figure 10.7 Partial density of states (PDOS) of (a) I1 and (b) I2 atoms in orthorhombic

CH

3

NH

3

PbI

3

crystals using the optB86b+vdWDF functional. (c) PDOS with summed contributions from

TiO

2

(dashed) and perovskite (solid) for the (110)

TiO

2

/CH

3

NH

3

PbI

3

(red) and

TiO

2

/CH

3

NH

3

PbI

3−

x

Cl

x

(blue) interfaces. The inset shows a zoom of the perovskites PDOS. The zero of the energy is set at the

TiO

2

conduction band minimum. . (d) Electron localization function contour plots with color scheme for the optimized

CH

3

NH

3

PbI

3

/TiO

2

interface.

Figure 10.8 (a) The average value of the internal structural parameters

z

and

w

(fractional displacement of Li and O along polar axis, respectively) from the MD simulations. The pyroelectric coefficient

Π

(triangles) is compared with experiment (circles; Ref. [135]) and direct MD results (diamonds). (b) The determined temperature dependence of the pyroelectric coefficient.

Figure 10.9 Predicted time dependence of the temperature in a cubic PZT nanodot under an AC electric field

E

(

t

) = [0.6 − 0.5 cos(2

πvt

)] × 10

9

V m

−1

with the frequency

v

 = 100 GHz

for (panel (a))

β

 = 0.95

and (panel (b))

β

 = 0.80

. The filled dots show the raw data while the solid line represents fitted

T

(

t

)

.

Figure 10.10 (a) The normalized dipole density

ρ

/

ρ

0

as a function of the angle

θ

and (b) distributions of microcanonical demon energies under applied electric field of 500 kV cm

−1

(thin line) and without electric field (thick line) at

T

= 300 K.

Figure 10.11 Schematic description of the energy storage characteristics (top panel) and ferroelectric domain structures (bottom panel) for (a) dielectric, (b) antiferroelectric, (c) relaxor ferroelectric and, (d) ferroelectric ceramics.

Figure 10.12 Calculated hysteresis loops for capacitors with (a) epitaxially constrained films and (b) “free” films of various thickness

l

and with dead layer

d

. (c) Temperature dependence of energy storage density of

BaTiO

3

.

Figure 10.13 (a) Phase transition in

PbZr

0.95

Ti

0.05

O

3

with mean amplitudes of various frozen‐in modes, in units of a.u., as functions of temperature. Schematic diagrams for the (b) orthorhombic and (c) rhombohedral structures and their relation to that of the pseudocubic cell in

PbZrO

3

. The indices pc, o, and f refer to the pseudocubic, orthorhombic, and rhombohedral cells, respectively. The solid circles represent the Pb atoms and

a

pc

is the pseudocubic lattice constant. (d) Energy (meV/f.u.) vs epitaxial strain (%) diagram. FE and AFE refer to the ferroelectric and antiferroelectric ground state, respectively. The “e” indicates epitaxial structures. Inset: Volume per f.u. (Å

3

) vs epitaxial strain (%) in the AFE region.

Chapter 11

Figure 11.1 Conductivities of PEO‐based polymer electrolytes with ceramic fillers. (a) Conductivity of PEO

8

LiClO

4

with different ceramic fillers (ferroelectric

BaTiO

3

, paraelectric

BaTiO

3

, and paraelectric

SrTiO

3

) as a function of filler concentration. (b) The ratio of the conductivity of composite (

PEO

8

LiClO

4

and

PEO

20

LiCF

3

SO

3

with different ceramic fillers) over the pristine one at 100 °C as a function of ferroelectric tetragonality.

Figure 11.2 Photos showing the electrolyte color change during discharge/charge of the composite cathode at C/2 rate within a voltage window between open circuit voltage and 1.5 V: (a) C/S cathode and (c) C/S+BTO composite cathode. Schematics of the polysulfide entrapment mechanism: (b) C/S cathode and (d) C/S+BTO composite cathode.

Figure 11.3 Electrochemical performance of the C/S composite cathode with and without the addition of ferroelectric BTO nanoparticles: (a) rate performance at different current densities, (b) charge/discharge curves, and (c) cycling performance at 0.2 C rate.

Figure 11.4 Schematics of the mechanism of FE‐OPV cell. (a) The formation of a singlet

charge‐transfer exciton

(

CTE

) at the donor–acceptor interface under the illumination of a photon and the dissociation of CTE can be achieved under a reverse bias electric field. (b) Structure of an OPV cell with thin ferroelectric P(VDF‐TrFE) layers, showing the electric field distribution and charge extraction. (c, d) Charge density and electrostatic potential distributions, under zero bias electric field, in the structure with semiconductor (S) and ferroelectric (FE) layers sandwiched between two metal electrodes (

M

1

and

M

2

).

Figure 11.5 Device performance of the cells with and without the insertion of one monolayer of P(VDF‐TrFE) FE film: (a)

I

–

V

curves and (b) dark current. The inset in (b) is the enlarged dark current.

Figure 11.6 Two‐phase crystal structure of

TMCM‐MnCl

3

. (A) The structural units of the low‐temperature phase:

MnCl

6

octahedron and cationic structure. (B) The structural units of the high‐temperature phase. (C) Projection of the low‐temperature structure. (D) Projection of the high‐temperature structure. H atoms are omitted for clarity.

Figure 11.7 Ferroelectric properties of polarization directions of

TMCM‐MnCl

3

. (a) The

P–E

hysteresis loop and current density versus bias voltage curves. (b) Piezoelectric

d

33

coefficients of some representative organic and inorganic ferroelectric materials. (c) Comparison of the local piezoelectric responses of some typical piezoelectric materials, measured by PFM. Inset: local piezoelectric response of

TMCM‐MnCl

3

as a function of applied voltage. (d) Twelve possible polarization directions in

TMCM‐MnCl

3

.

Figure 11.8 (a) Redox potentials between Pd nanoparticle catalyst,

BaTiO

3

, and neutral aqueous surrounding relative to standard hydrogen electrode are compared for selected species. (b) Schematic drawing showing the possible redox reactions at the polarized surface of

BaTiO

3

particles under the pyroelectric effect.

Figure 11.9 Crystal structure of V‐doped

BiOIO

3

(

BiOI

0.926

V

0.074

O

3

) in the (a)

ab

and (b)

bc

planes. The polarization direction is indicated by black arrows. (c)

Second harmonic generation

(

SHG

) for

BiOIO

3

and

BiOI

0.926

V

0.074

O

3

. (d) Schematic showing the mechanism of ROS generation under mechanical actuation. (e)

·

O

2

−

and (f)

·

OH

evolution curves of

BiOIO

3

and

BiOI

0.926

V

0.074

O

3

under ultrasonication (40 kHz, 300 W).

Guide

Cover

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Ferroelectric Materials for Energy Applications

Haitao Huang and James F. Scott

Copyright

Editors

Prof. Haitao Huang

Hong Kong Polytechnic University

Department of Applied Physics

BC620

Hung Hom, Kowloon

Hong Kong

Prof. James F. Scott

University of St Andrews

School of Chemistry

Purdie Building

North Haugh

KY16 9AJ St Andrews

United Kingdom

Cover image: © nadla/iStockphoto

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Preface

Ferroelectric materials are well‐known for their switchable spontaneous polarizations that are responsive to external stimuli, such as stress, temperature, electric field, and magnetic field (for multiferroic materials). Hence, ferroelectrics are often called “smart materials” and have found wide applications in sensors and actuators, as well as memory devices and field effect transistors, etc. Recent years have witnessed the emerging of ferroelectric materials in various kinds of energy harvesting, conversion, and storage devices. This is a relatively new and rapidly developing area, which we would like to call it “ferro‐energy.” In order to attract more researchers and engineers to work in this fascinating area, we invited a group of leading scientists to give comprehensive and timely reviews on various topics of ferroelectric materials for energy‐related applications. For the benefit of young graduate students and novices in this area, the book starts from the fundamentals of ferroelectric materials. The next few chapters are mainly focused on applications including, but not limited to, piezoelectric energy generation, ferroelectric photovoltaics, pyroelectric energy harvesting, electrocaloric cooling, electric energy storage, photocatalysis, etc. First‐principles calculations are reviewed in a separate chapter, which can be used as a powerful tool to explain or even predict the material properties for energy‐related applications. Finally, the future perspectives of ferroelectrics for energy are summarized.

Due to their unique responsive spontaneous polarizations, ferroelectric materials will play an important role in energy‐related applications that cannot be replaced by other conventional energy materials. This is also one of our purposes for the compilation of this book. This book is aimed at researchers working on ferroelectric materials and energy materials, where experts in this area can find it a useful resource book, engineers can have a broadened view after reading and beginners can be led quickly to the forefront of this area.

Haitao Huang

Hong Kong Polytechnic University

James F. Scott

University of St Andrews

1Fundamentals of Ferroelectric Materials

Ling B. Kong1, 2, Haitao Huang3, and Sean Li4

1Shenzhen Technology University, College of New Materials and New Energies, 3002 Lantian Road, Shenzhen, Guangdong, 518118, PR China

2Nanyang Technological University, School of Materials Science and Engineering, 50 Nanyang Avenue, Singapore, 639798, Singapore

3Hong Kong Polytechnic University, Department of Applied Physics, 11 Yuk Choi Road, Hung Hom, Kowloon, Hong Kong

4The University of New South Wales, School of Materials Science and Engineering, High Street, Kensington, Sydney, NSW, 2052, Australia

1.1 Introduction

Ferroelectricity is defined as the property of a material, with two characteristics, i.e. (i) spontaneous polarization is present and (ii) it is reversible when subjected to external electric fields [1]. The property was first observed in Rochelle salt and is named so because of its analogy to ferromagnetism, which is a magnetic property of a material that has a permanent magnetic moment [2, 3]. Other similarities include hysteresis loop, Curie temperature (TC), domains, and so on. The prefix, ferro, meaning iron (Fe), was used at that time because of the presence of the element in the magnetic materials. However, ferroelectricity has nothing to do with Fe. Even though some ferroelectric materials contain Fe, it is not the originating factor.

Generally, as a material is polarized by an external electric field, the induced polarization (P) is linearly proportional to the magnitude of the applied external electric field (E), which is known as dielectric polarization. Above the Curie temperature TC, ferroelectric materials are at a paraelectric state. In this case, a nonlinear polarization is present versus an external electric field. As a result, electric permittivity, according to the slope of the polarization curve, is not a constant. At the ferroelectric state, besides the nonlinearity, a spontaneous nonzero polarization was present, as the applied field (E) is zero. Because the spontaneous polarization can be reversed by a sufficiently strong electric field, it is dependent on the currently applied electric field and the history as well, thus leading to the presence of the hysteresis loop.

The electric dipoles in a ferroelectric material are coupled to the crystal lattice of the material, so that the variation in lattice could change the strength of the dipoles, i.e. the strength of the spontaneous polarization. The change in the spontaneous polarization, in turn, leads to a change in the surface charge, which causes current flow when a ferroelectric material is made into a capacitor without the application of an external field across it. There are two stimuli that can be used to change the lattice structure of a ferroelectric material, i.e. (i) mechanical force and (ii) temperature. The generation of surface charge as a result of the application of an external stress is known as piezoelectricity, while the change in spontaneous polarization in response to the change in temperature is named as pyroelectricity.

To understand ferroelectricity, it is necessary to link with piezoelectricity and pyroelectricity, because they have interesting interrelationships in terms of crystal structures. All crystals can be categorized into 32 different classes. In the theory of point groups, these classes are determined by using several symmetry elements: (i) center of symmetry, (ii) axis of rotation, (iii) mirror planes, and (iv) several combinations of them. The 32 point groups are subdivisions of seven basic crystal systems that are, in order of ascending symmetry, triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral (trigonal), hexagonal, and cubic. Out of the 32 point groups 21 classes are non‐centrosymmetric, which is a necessary condition for piezoelectricity to exist. Twenty of them are piezoelectric.

Among the 20 piezoelectric crystal classes, 10 crystals have pyroelectric properties. Within a given temperature range, this group of materials is permanently polarized. Compared to the general piezoelectric polarization produced under stress, pyroelectric polarization develops spontaneously and remains as permanent dipoles in the structure. Because this polarization varies with temperature, the response is named as pyroelectricity. Within the pyroelectric group, there is a subgroup that has spontaneous polarization, which is the ferroelectric materials. On one hand, the polarization in a ferroelectric material is similar to that in a pyroelectric one. On the other hand, these two polarizations are different, because ferroelectric polarization is reversible by an external applied electric field. Therefore, ferroelectricity is defined as the presence of spontaneous polarization that is reversible by an external electric field [4, 5]. Figure 1.1 summarizes the interrelationship among piezoelectric, pyroelectric, and ferroelectric materials, together with general dielectrics. This relationship implies that ferroelectric materials have the highest piezoelectric performance compared to non‐ferroelectric materials.

Figure 1.1 Interrelationship among piezoelectric, ferroelectric, pyroelectric, and dielectric materials. Ferroelectric materials have superior pyroelectric, piezoelectric, and dielectric properties than non‐ferroelectric materials.

According to Ginzburg–Landau theory, the free energy of a ferroelectric material, without the application of an external electric field and stress, can be expressed as a Taylor expansion in terms of the order parameter, polarization (P) [6]. When a sixth order expansion is used, i.e. the eighth order and higher terms are neglected, the free energy is given by

1.1