Piezoelectric Materials E-Book

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Seitenzahl: 1219

Veröffentlichungsjahr: 2024

Beschreibung

Piezoelectric Materials

Analyze the foundational materials of the electronics industry

In recent years piezoelectric materials have become one of the world’s most important classes of functional materials. Their ability to convert between mechanical and electrical energy makes them indispensable for sensors, transducers, actuators, catalysts, and many other foundational electronic devices. As electronics industries expand at unprecedented rates, the range of applications for piezoelectric materials continues to grow.

Piezoelectric Materials offers a comprehensive overview of this group of materials, its key properties, and its applications. Beginning with the fundamental science of piezoelectric phenomena, it then analyzes different the numerous different classes of piezoelectric materials and their current and future industrial functions. The result is essential for engineers and materials scientists working in any number of areas.

Piezoelectric Materials readers will also find:

• Analysis of materials types include lead-based and lead-free piezoelectric materials, textured piezoceramics, piezoelectric thin films, and many more
• Detailed discussion of applications including dielectric energy storage and biomedical technology
• Authorship by a leading researcher of piezoelectric materials

Piezoelectric Materials is ideal for materials scientists, electronic engineers, polymer chemists, solid state chemists, and any other researchers or professionals working with these key materials.

Leseprobe

Piezoelectric Materials

From Fundamentals to Emerging Applications

Volume 1

Edited by Jiagang Wu

Piezoelectric Materials

From Fundamentals to Emerging Applications

Volume 2

Edited by Jiagang Wu

The Editor

Prof. Jiagang Wu

Sichuan University

No. 24 South Section 1

Yihuan Road

Chengdu

CH, 610065

Cover Image: © Yuichiro Chino/Getty Images

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© 2024 WILEY‐VCH GmbH, Boschstraße 12, 69469 Weinheim, Germany

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Print ISBN: 978‐3‐527‐35470‐2

ePDF ISBN: 978‐3‐527‐84121‐9

ePub ISBN: 978‐3‐527‐84122‐6

oBook ISBN: 978‐3‐527‐84123‐3

The Editor

Prof. Jiagang Wu

Sichuan University

No. 24 South Section 1

Yihuan Road

Chengdu

CH, 610065

Cover Image: © Yuichiro Chino/Getty Images

All books published by WILEY‐VCH are carefully produced. Nevertheless, authors, editors, and publishers do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details, or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing‐in‐Publication Data A catalog record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.

© 2024 WILEY‐VCH GmbH, Boschstraße 12, 69469 Weinheim, Germany

All rights reserved (including those for translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978‐3‐527‐35471‐9

ePDF ISBN: 978‐3‐527‐84121‐9

ePub ISBN: 978‐3‐527‐84122‐6

oBook ISBN: 978‐3‐527‐84123‐3

Preface

Piezoelectricity, a phenomenon wherein a material generates electrical charges on its surfaces in response to applied mechanical stress or, conversely, yields mechanical strain when subjected to an electric field, serves as a critical bridge between mechanical and electrical energies. This unique functionality has spurred the widespread adoption of piezoelectric materials across a broad spectrum of modern technologies. Examples of these technologies abound and pervade our daily lives. In the realm of consumer electronics, piezoelectric sensors and actuators are integral components of smartphones, enabling precision touch‐screen interactions. In the medical field, piezoelectric probes are indispensable in ultrasonic diagnostic equipment, facilitating noninvasive imaging and diagnostic procedures. Additionally, high‐precision positioning units in scientific research equipment, ignitors for lighters, and pressure sensors, all leverage the properties of piezoelectric materials to function effectively.

Piezoelectric materials can be categorized based on the form of matter, with classifications including piezoelectric ceramics, single crystals, thin films, and organic materials. Each category boasts specific characteristics, making them ideal for particular applications. Moreover, in alignment with escalating global concerns for environmental protection and sustainable development, piezoelectric materials are often classified as lead‐containing or lead‐free. This classification underscores the ongoing pursuit of environmentally friendly materials that can deliver the advantages of piezoelectricity without compromising sustainability. The evolving research and development in this field promise exciting advancements and wider adoption of piezoelectric materials in future technologies.

Over the past two decades, the field of piezoelectric materials and associated devices has undergone swift and significant advancements. Both phase‐field simulations and neutron scattering experiments have substantiated the exceptional influence of polar nanoregions, which have been instrumental in enhancing the piezoelectric properties of lead‐based ceramics and single crystals. Innovative approaches, including new phase boundary engineering and compositional design, have equipped lead‐free piezoelectric materials with superior piezoelectricity, which is comparable to some of their lead‐free counterparts. The adoption of a multi‐scale structural design strategy has consistently shattered previous records in dielectric energy storage, signaling the potential for further advancements in this area. Concurrently, the evolution of microfabrication technology has facilitated the emergence of piezoelectric materials' enticing transduction capabilities in a variety of cutting‐edge electronic devices. These include biomedical devices, piezoelectric nanogenerators, and piezoelectric flexible devices, which embody the intersection of technological progress and practical application. Additionally, the utilization of advanced in situ characterization techniques, including transmission electron microscopy, neutron scattering, and high‐energy synchrotron radiation, has empowered the researchers to unravel the complex physical mechanisms underlying the observed high performance. These advancements collectively signal a bright future for the continued development and application of piezoelectric materials.

Motivated by the aforementioned advancements, I contend that the present moment provides an opportune juncture for reviewing the research landscape of piezoelectric materials and devices. Such a book proves imperative, not only for early career researchers seeking an informed entry point into the field but also for established scholars aiming to conceptualize and implement novel strategies for enhancing the performance of piezoelectric materials and devices. Although numerous high‐quality reviews and books have been previously published, the majority concentrate on specific topics within individual material systems. To obtain a holistic understanding of the field of piezoelectric materials and devices, it is essential to encompass both the fundamental knowledge of piezoelectricity and the state‐of‐the‐art research progress in piezoelectric materials and devices. Bearing this objective in mind, I have undertaken the compilation of this book. My aspiration is that this work will serve as a comprehensive resource, illuminating the path for future research and development in the realm of piezoelectric materials and devices.

This book comprises 20 chapters that delve into various facets of piezoelectricity, a dynamic and evolving field. Chapter 1 provides a solid foundation in the basic principles of piezoelectricity, delineating piezoelectric coefficients, describing piezoelectricity via third‐rank tensor, and discussing symmetry considerations. This opening chapter serves as an invaluable resource for readers unfamiliar with piezoelectricity or those seeking to strengthen their foundational understanding. Chapter 2 explores the probing of piezoelectric effects using X‐ray diffraction and the observation of the piezoelectric effect in multidomain ferroelectrics. Chapter 3 offers a succinct summary of the evolution and research advancements in lead‐based piezoelectric materials, with emphasis on historical progress and modern‐day applications. Chapters 4 and 5 deliver a comprehensive overview of lead‐free piezoelectric materials, concentrating on four significant material systems: (K, Na)NbO3, BaTiO3, (Bi, Na)TiO3, and BiFeO3. Chapter 6 presents an overview of piezoelectricity in molecular ferroelectrics, focusing on piezoelectricity in different molecular ferroelectrics and piezoresponse force microscopy (PFM)‐aided characterization and design. Chapters 7 and 8 review the development and research of BiScO3–PbTiO3 and Bi4Ti3O12‐based high‐temperature piezoelectric ceramics, covering aspects like characteristics, fabrication, domain engineering, electrical properties, endurance, and high‐temperature applications. Chapter 9 delves into the newly developed texturing method, concentrating on textured piezoceramics, texture–property relationships, and device applications of textured piezoceramics. Chapter 10 reviews the strides made in piezoelectric thin films, focusing particularly on the growth and piezoelectric coefficient measurements of these thin films. Chapter 11 reviews the development of piezoelectric and electro‐optic properties in lead‐free single crystals, with a focus on (K, Na)NbO3 and K(Ta, Nb)O3‐based single crystals. Chapter 12 summarizes the electrostrictive effect, touching on its fundamentals and history, reviewing the electrostrictive effect and strain in various ferroelectrics, and providing examples of their applications. Chapters 13 and 14 review ferroelectric materials for dielectric energy storage, including the fundamentals, design, and performance of inorganic, organic, and composite dielectric materials, as well as their applications. Chapter 15 reviews the advances of the electrocaloric effect, concentrating on its occurrence in ceramic films, bulk ceramics, single crystals, and multi‐layer ceramics (MLCs), and the designs and demonstrations of ceramics‐based cooling devices. Chapter 16 reviews piezo‐bioelectronic materials and emerging applications, including materials, fabrication, and emerging biomedical applications of piezo‐bioelectronic devices. Chapter 17 reviews the advances of porous piezoelectric materials for energy technologies, concentrating on the types, fabrication techniques, modeling and characterization, and applications of porous piezoelectric materials. Chapter 18 reviews piezoelectric flexible devices, including their working mechanism, materials, structure design, and applications. Chapter 19 reviews the advances of ferroelectrics under compression, including lead‐based and lead‐free ferroelectrics and their applications. In Chapter 20, the advances of piezoelectricity in biomedical applications are reviewed, concentrating on several representative applications including implantable energy harvesters, ultrasound imaging transducers, bone/tissue regeneration, neural stimulation, and cancer therapy. Each chapter concludes with a section on the future perspective and concluding remarks.

Finally, it is my sincere hope that this book will serve as a valuable resource for those interested in the fascinating world of piezoelectric materials and devices. The broad array of topics covered, from fundamental concepts to cutting‐edge research, aims to provide readers with a comprehensive understanding of the field. This book is a testament to the collective efforts of numerous researchers, scientists, and scholars whose contributions have significantly advanced our understanding of piezoelectric materials and their multifaceted applications.

In closing, I would like to emphasize my deep appreciation to all those who have contributed to this endeavor. The work presented herein represents the synthesis of many minds and the culmination of considerable effort. I trust that this book will provide readers with a compelling and enlightening exploration of the world of piezoelectrics.

February 26, 2024

Jiagang WuSichuan University

1Piezoelectric Coefficients and Crystallographic Symmetry

Semën Gorfman1 and Nan Zhang2

1Tel Aviv University, The Department of Materials Science and Engineering, Ramat Aviv, Tel Aviv, 6997801, Israel

2Xi'an Jiaotong University, School of Electronic Science and Engineering, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, 28 West Xianning Road, Xi'an, 710049, China

1.1 Introduction

Piezoelectricity is the ability of some crystals to convert mechanical and electrical energy into each other. The direct piezoelectric effect describes the linear dependence of electric polarization in a crystal on applied external mechanical stress. The converse piezoelectric effect then describes the linear dependence of the mechanical deformation in a crystal on an applied external electric field. Piezoelectricity possesses many useful applications, such as pressure sensors/actuators [1], transducers [2], piezoelectric motors [3], sonars, and microelectromechanical systems (MEMs) [4]. The market for piezoelectric devices is projected to reach US$41.0 billion by 2027. Over the last few decades, piezoelectricity has been the subject of considerable academic research, review papers, and monographs [5, 6]. In this chapter, we introduce the anisotropy of piezoelectric coefficients and their relationship with the crystallographic symmetry of materials.

1.2 On the Anisotropy of Piezoelectricity and Its Role in the Understanding of Structures of Crystalline Materials

Incidentally, the discovery of piezoelectricity played a key role in the evolution of ideas concerning the periodic atomic structures of crystals. Notably, such periodicity was only a hypothesis at that time and was experimentally proven later in 1912 by Max von Laue [7]. Piezoelectricity presented one of those first physical properties that highlighted the anisotropy (directional dependence) of single crystals. Indeed, an isotropic material cannot be piezoelectric: the development of polarization under applied stress means that at least the opposite ends of the polarization vector are different; hence, a crystal must be anisotropic in order to be piezoelectric. The performance of a piezoelectric device strongly depends on its orientation relative to the lattice basis vectors. Figure 1.1 presents one particular example of the anisotropic longitudinal piezoelectricity in α‐quartz.

Figure 1.1 Schematic illustration of the anisotropy of piezoelectric effect in α‐quartz: (a) typical natural shape of quartz crystal with three non‐coplanar directions along the basis vectors of the reciprocal lattice , (b) the directional dependence of the magnitude of longitudinal piezoelectric coefficient (see the definition in the next paragraph). Remarkably, α‐quartz develops no polarization under uniaxial strain along axis (parallel to the threefold symmetry axis) and does not deform under electric field parallel to axis.

Source: Semën Gorfman.

In homogeneous single crystals, the anisotropy of properties must originate from the intrinsic asymmetry of atomic structures maintained over macroscopically long distances. This can only be possible if the structure is long‐range‐ordered. This is why anisotropy of crystals in general and piezoelectricity of crystals in particular are the key ingredients for the idea of periodicity/long‐range order of crystals.

1.3 Simplified Definitions of Piezoelectric Coefficients

As for any anisotropic physical property, the description of piezoelectricity requires handling several property coefficients. There are very few classes of piezoelectric crystals where only one independent coefficient is sufficient (e.g. Bi12SiO20[8]). However, prior to introducing the proper tensor description of the piezoelectricity, we will inspect the simplified didactical definitions and understand the physical meaning of piezoelectric coefficients. Specifically, we will assume that a piezoelectric device has been prepared as a parallel plate capacitor, whereas mechanical stress, electric field, polarization, and deformation appear along the plate normally only (Figure 1.2).

Figure 1.2 Simplified definitions of direct and converse piezoelectric effect: (a) the uniaxial stress σ is applied normally to the piezoelectric plate and causes polarization ΔP = d · σ with the positive and negative charges emerging outside the plate face, (b) electric field is applied normally to the piezoelectric plate with the change of the plate thickness so that x = d · E. Here, x = Δl/l. The shape of the deformed plate is shown by the dashed rectangle.

Source: Semën Gorfman.

1.3.1 Direct Piezoelectric Effect

The simplified definition of direct piezoelectric effect is:

(1.1)

here, ΔP is the projection of the change in the polarization vector to the plate normal and σ is the pressure of the uniaxial forces normally applied to the plate. σ is positive/negative for extending/compressing forces. d is the direct piezoelectric coefficient. The units of polarization and stress are and ; therefore, the units of the piezoelectric coefficient are or (practically used) . This magnitude becomes more intuitive if we rewrite (1.1) as:

(1.2)

Here, F = σ · S is the magnitude of the force applied to the plate, Q = ΔP · S is the electric charge outside the plate due to the increment of the polarization. S is the area of each face. According to (1.2), direct piezoelectric coefficient is the amount of electric charges accumulated outside the crystal plate per force applied to the plate. Thus, 1 N applied to a 1 pC/N piezoelectric plate will release 1 pC on the plate faces (positive on one side and negative on the opposite side).

1.3.2 Converse Piezoelectric Effect

Similarly, the simplified definition of the converse piezoelectric effect is:

(1.3)

Here, E is the projection of the electric field vector to the plate normal, x = Δl/l is the relative expansion of the plate. x is positive/negative for expansion/contraction. l is the thickness of the crystal plate. d is the converse piezoelectric coefficient. The units of converse piezoelectric coefficient are or, in practical terms, . To get an impression about this unit, we can reformulate (1.3) as:

(1.4)

Here, U = E · l is the voltage falling between the faces of the plate. Thus, converse piezoelectric coefficient is the elongation of the plate per applied voltage. For example, the application of 1000 V to a 1 pm/V piezoelectric crystal plate expands or shrinks by 1 nm.

1.3.3 On the Equivalence of Direct and Converse Piezoelectric Coefficients

It can be easily shown that the units of are equivalent to . This equivalence raises the question of whether there exists any relationship between the direct and converse piezoelectric coefficients. Indeed, these coefficients are not just related; if defined exactly as in Eqs. (1.1) and (1.3), they are numerically equal to each other. This is the reason why the same symbol d for the direct and converse piezoelectric coefficients can be retained. However, only for this paragraph, we will temporarily introduce the notations d(d) and d(c) for the direct and converse piezoelectric coefficients, correspondingly.

Here, we will look back at Lippmann's original theory [9] for the longitudinal direct Eq. (1.1) and converse Eq. (1.3) effects only. The interested reader may refer to Nye's book [10] for a comprehensive description of the matter. We assume that a small variation of external mechanical stress, dσ, and electric field, dE, results in the increments of mechanical strain, dx, and polarization, dP. The first law of thermodynamics expresses the conservation of energy during the electric polarization and mechanical deformation of the material as:

(1.5)

Here, dU is the change in the internal energy of the crystal, δQ is the amount of energy received by the crystal in the form of heat, δA is the amount of energy received by the crystal in the form of work by the external electric (δAE = E · dP) and mechanical (δAM = σ · dx) forces [10]. All the quantities are expressed per unit volume of the material. Assuming no heat exchange with the environment (δQ = 0 otherwise, further caloric physical properties would be involved), we can rewrite (1.5) as:

(1.6)

Introducing Φ = U − E · P − σ · x, we can rewrite (1.6)

(1.7)

Because Φ is a full differential, the polarization and strain can be expressed as partial derivatives:

(1.8)

On the other hand, equations (1.1) and (1.3) can also be rewritten in the form of partial derivatives, where represents the direct piezoelectric effect and represents the converse piezoelectric effect. The equivalence between d(d) and d(c) follows immediately as:

(1.9)

Table 1.1 Typical orders of magnitude of piezoelectric coefficients.

Material

d

(pC/N)

Refs.

Material

d

(pC/N)

References

α

‐quartz (SiO

2

)

2

[11]

BaTiO

3

150

[12]

PVDF

20

[13]

PbZr

0.52

Ti

0.48

O

3

(PZT ceramics)

200–400

[14]

Al

0.67

Sc

0.33

N

26

[15]

PMN–PT single crystals

2000

[16]

Bi

12

SiO

20

40

[8]

Sm‐doped PMN–PT single crystals

3400–4100

[17]

This is because the second derivative does not depend on the order of variables.

This remarkable feature, appearing in the form of “conjugated” pairs, also holds for many other properties. For example, pyroelectricity is conjugated with the electrocaloric effect and thermal expansion is conjugated with the piezocaloric effect.

1.3.4 Typical Values of Piezoelectric Coefficients

Following our understanding of the piezoelectric coefficient units, it is worth observing their typical values. Table 1.1 lists the piezoelectric coefficients of a few selected materials. Notably, the table here is merely for the purpose of obtaining an impression regarding the typical magnitude of piezoelectric coefficients. As will be discussed in the following chapters, piezoelectric coefficients are described by tensors, and each material may have few coefficients that may differ from one another by an order of magnitude. Still, it is clear from the table that piezoelectric coefficients of most known materials are below 2000 pC/N. Only in so‐called relaxor ferroelectric single crystals of PbMg1/3Nb2/3O3–PbTiO3 (PMN–PT) [16, 18] and their derivatives [17], piezoelectric coefficients may exceed such high values.

1.4 Description of Piezoelectricity by Third‐rank Tensor

1.4.1 Tensor of Piezoelectric Coefficients

Piezoelectricity of single crystals must be described by tensors. For the direct piezoelectric effect:

(1.10)

Here, ΔPk represents the components of the change in the polarization vector, σij represents the components of the second‐rank stress tensor, and dkij represents the components of the third‐rank tensor of direct piezoelectric coefficients. More information about the meaning of the stress and strain tensors can be found in [10, 19, 20]. The indices i, j, k run between 1 and 3, and the Einstein summation rule applies to every repeated index (i and j in this case). The vector and tensor components are expressed as relative to a Cartesian coordinate system e1, e2, e3. Later, we will elaborate on the crucial role of this Cartesian system.

According to Eq. (1.10), dkij describes the polarization increment along the Cartesian ek axis due to the force applied along the ei to the surface, which is normal to ej. For example, if the piezoelectric coefficient d233 is nonzero, then the polarization along the e2 axis will develop in response to the tensile mechanical stress on the face, normal to e3. If, for example, the piezoelectric coefficient d123 is nonzero, then the polarization along the e1 will develop due to the shearing stress on the face normal to the e3 but in the direction of e2.

For the converse piezoelectric effect:

(1.11)

Here, xij represents the components of the second‐rank strain tensor and Ek represents the components of the electric field vector. In this case, the Einstein summation applies over the repeated index k. According to (1.11), the converse piezoelectric coefficient, dkij, describes the strain component, xij , in response to the electric field along the Cartesian ek axis. For example, the converse piezoelectric coefficient d233 stands for the elongation along the e3 in response to an electric field applied along e2. The converse piezoelectric coefficient d123 describes the shear strain in the e2e3 plane due to electric field along e1.

The thermodynamics of the piezoelectric effect remains similar to the simplified case considered earlier in this chapter. Specifically, if expressed in the same Cartesian coordinate system, all the components of the direct piezoelectric tensor are numerically equal to those for the converse piezoelectric tensor. However, it is crucial that the tensor components are defined exactly as in (1.10) and (1.11), i.e. the first index is “electric,” while the second and the third indices are “mechanical.”

1.4.2 Voigt/Matrix Notation for Piezoelectric Coefficient

Any third‐rank tensor has a maximum of 27 = 33 independent components. However, their real number is smaller because of the symmetry. There are two types of symmetries: the first is physical and appears as a consequence of energy, charge, and momentum conservation laws. The second is crystallographic, which is inherited from the geometrical symmetry of crystal structures and expressed in the form of the Neumann principle. For piezoelectricity, the physical symmetry results in the invariance with respect to the interchange of “mechanical” indices:

(1.12)

Equation (1.12) is valid for any piezoelectric material, regardless of which atomic structure it contains. This property is intuitively related to similar symmetry properties of the strain and stress tensors xij = xji, σij = σji. This symmetry means that the pair ij may cover six different variants: 11, 22, 33, 23 ≡ 32, 13 ≡ 31, 12 ≡ 21. For writing compactness reasons, a special indexing scheme is commonly used (first introduced by Voigt [21]). The pair ij can be replaced by a single index m = 1…6, according to Table 1.2.

Table 1.2