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Special Issue "Piezoelectric Materials"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Energy Materials".

Deadline for manuscript submissions: closed (30 September 2015)

Special Issue Editor

Guest Editor
Prof. Dr. Lorena Pardo

Department of Materials for the Information Technologies. Institute of Materials Science of Madrid, Consejo Superior de Investigaciones Científicas (ICMM-CSIC). c/Sor Juana Inés de la Cruz, 3. Cantoblanco. 28049-Madrid, Spain
Website | E-Mail
Interests: ferroelectric materials; piezoelectricity; dielectric properties; pyroelectric properties; mechanical properties; ceramics; ferroelectric domains; phase transitions; structure determination; microstructure and texture determination; composite materials; lead-free piezoceramics; photovoltaics; energy harvesting; energy storage; electromechanical resonances; ultrasonic generation

Special Issue Information

Dear Colleagues,

Piezoelectric materials constitutes a well-established, yet dynamic, field of research activities with numerous practical applications, such as sensors and actuators, covering almost all human activities (communications, transport, health, energy, manufacture and quality control to name a few). The piezoelectricity (conversion of mechanical into electrical energy and vice versa) was discovered by Pierre and Jacques Curie in 1880. It characterizes non-centrosymmetric materials, such as quartz, hidroxyapatite of the bones, or drawn silk films. Ferroelectrics are a special class of piezoelectrics, being multifunctional crystals whose structure possesses a spontaneous dipole which can switch between two equilibrium states. The piezoelectricity of barium titanium oxide (BaTiO3) ceramics, i.e., randomly oriented ionic policrystals, therefore isotropic and centrosymmetric materials, remained unexplained until 1944. At this time, the role of “poling” by an applied electric field, which causes ferroelectric dipole orientation, was understood. From that date, scientific areas concerning ferro-piezoelectric materials such as ceramics, composites, single-crystals and thin films have grown steadily wider. An increasing effort has been devoted to obtain high sensitivity and lead-free composition materials since 2003. This was driven by the toxicity of lead oxide, the main component of commercial Pb(Zr,Ti)O3 (PZT) ceramics, and by current directives for environmental protection, demanding the elimination of lead from the piezoelectric components in devices. This remains a primary scientific challenge. Mechanical strains generated by the piezoelectric effect in ferroelectric oxides are relatively low and must be amplified for practical purposes. Field-induced structural phase transitions are among those mechanisms that can generate a massive mechanical strain, one order of magnitude higher than the piezoelectric one in ferroelectric oxides with a perovskite-type structure. Such a mechanism has recently led to a new generation of non-linear actuators. Advances in characterization techniques, ultra-high electromechanical response, energy harvesting using piezoelectrics, flexoelectricty or piezoelectronics are other examples of recent topics of interest within this field.

Lorena Pardo
Guest Editor

Manuscript Submission Information

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Keywords

  • Processing of piezoelectric materials (ceramics, composites, single-crystals, etc.)
  • Lead-free piezoelectric materials
  • Structure-properties relationships in piezoelectric materials
  • Morphotropic and polymorphic phase boundaries in ferro-piezoelectric perovskites
  • Poling of ferro-piezoelectrics and electric field-induced transitions
  • Determination of piezoelectric, dielectric and elastic material coefficients from impedance at electromechanical resonance
  • Non-linear properties and characterization of piezoelectric materials

Published Papers (17 papers)

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Research

Jump to: Review

Open AccessFeature PaperArticle Compositional Design of Dielectric, Ferroelectric and Piezoelectric Properties of (K, Na)NbO3 and (Ba, Na)(Ti, Nb)O3 Based Ceramics Prepared by Different Sintering Routes
Materials 2016, 9(3), 179; doi:10.3390/ma9030179
Received: 14 December 2015 / Revised: 2 March 2016 / Accepted: 2 March 2016 / Published: 8 March 2016
Cited by 3 | PDF Full-text (3676 KB) | HTML Full-text | XML Full-text
Abstract
Lead free piezoelectric materials are being intensively investigated in order to substitute lead based ones, commonly used in many different applications. Among the most promising lead-free materials are those with modified NaNbO3, such as (K, Na)NbO3 (KNN) and (Ba, Na)(Ti,
[...] Read more.
Lead free piezoelectric materials are being intensively investigated in order to substitute lead based ones, commonly used in many different applications. Among the most promising lead-free materials are those with modified NaNbO3, such as (K, Na)NbO3 (KNN) and (Ba, Na)(Ti, Nb)O3 (BTNN) families. From a ceramic processing point of view, high density single phase KNN and BTNN ceramics are very difficult to sinter due to the volatility of the alkaline elements, the narrow sintering temperature range and the anomalous grain growth. In this work, Spark Plasma Sintering (SPS) and high-energy ball milling (HEBM), following heat treatments (calcining and sintering), in oxidative (O2) atmosphere have been used to prepare single phase highly densified KNN (“pure” and Cu2+ or Li1+ doped), with theoretical densities ρth > 97% and BTNN ceramics (ρth - 90%), respectively. Using BTTN ceramics with a P4mm perovskite-like structure, we showed that by increasing the NaNbO3 content, the ferroelectric properties change from having a relaxor effect to an almost “normal” ferroelectric character, while the tetragonality and grain size increase and the shear piezoelectric coefficients (k15, g15 and d15) improve. For KNN ceramics, the results reveal that the values for remanent polarization as well as for most of the coercive field are quite similar among all compositions. These facts evidenced that Cu2+ may be incorporated into the A and/or B sites of the perovskite structure, having both hardening and softening effects. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessFeature PaperArticle Revisiting the Characterization of the Losses in Piezoelectric Materials from Impedance Spectroscopy at Resonance
Materials 2016, 9(2), 72; doi:10.3390/ma9020072
Received: 10 November 2015 / Revised: 22 December 2015 / Accepted: 19 January 2016 / Published: 26 January 2016
Cited by 4 | PDF Full-text (5957 KB) | HTML Full-text | XML Full-text
Abstract
Electronic devices using the piezoelectric effect contain piezoelectric materials: often crystals, but in many cases poled ferroelectric ceramics (piezoceramics), polymers or composites. On the one hand, these materials exhibit non-negligible losses, not only dielectric, but also mechanical and piezoelectric. In this work, we
[...] Read more.
Electronic devices using the piezoelectric effect contain piezoelectric materials: often crystals, but in many cases poled ferroelectric ceramics (piezoceramics), polymers or composites. On the one hand, these materials exhibit non-negligible losses, not only dielectric, but also mechanical and piezoelectric. In this work, we made simulations of the effect of the three types of losses in piezoelectric materials on the impedance spectrum at the resonance. We analyze independently each type of loss and show the differences among them. On the other hand, electrical and electronic engineers include piezoelectric sensors in electrical circuits to build devices and need electrical models of the sensor element. Frequently, material scientists and engineers use different languages, and the characteristic material coefficients do not have a straightforward translation to those specific electrical circuit components. To connect both fields of study, we propose the use of accurate methods of characterization from impedance measurements at electromechanical resonance that lead to determination of all types of losses, as an alternative to current standards. We introduce a simplified equivalent circuit model with electrical parameters that account for piezoceramic losses needed for the modeling and design of industrial applications. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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Open AccessFeature PaperArticle Development of Porous Piezoceramics for Medical and Sensor Applications
Materials 2015, 8(12), 8877-8889; doi:10.3390/ma8125498
Received: 4 November 2015 / Revised: 4 December 2015 / Accepted: 10 December 2015 / Published: 21 December 2015
Cited by 4 | PDF Full-text (2899 KB) | HTML Full-text | XML Full-text
Abstract
The use of porosity to modify the functional properties of piezoelectric ceramics is well known in the scientific literature as well as by the industry, and porous ceramic can be seen as a 2-phase composite. In the present work, examples are given of
[...] Read more.
The use of porosity to modify the functional properties of piezoelectric ceramics is well known in the scientific literature as well as by the industry, and porous ceramic can be seen as a 2-phase composite. In the present work, examples are given of applications where controlled porosity is exploited in order to optimise the dielectric, piezoelectric and acoustic properties of the piezoceramics. For the optimisation efforts it is important to note that the thickness coupling coefficient kt will be maximised for some non-zero value of the porosity that could be above 20%. On the other hand, with a good approximation, the acoustic velocity decreases linearly with increasing porosity, which is obviously also the case for the density. Consequently, the acoustic impedance shows a rather strong decrease with porosity, and in practice a reduction of more than 50% may be obtained for an engineered porous ceramic. The significance of the acoustic impedance is associated with the transmission of acoustic signals through the interface between the piezoceramic and some medium of propagation, but when the porous ceramic is used as a substrate for a piezoceramic thick film, the attenuation may be equally important. In the case of open porosity it is possible to introduce a liquid into the pores, and examples of modifying the properties in this way are given. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessArticle Piezoelectric, Mechanical and Acoustic Properties of KNaNbOF5 from First-Principles Calculations
Materials 2015, 8(12), 8578-8589; doi:10.3390/ma8125477
Received: 24 September 2015 / Revised: 13 October 2015 / Accepted: 12 November 2015 / Published: 9 December 2015
Cited by 3 | PDF Full-text (1837 KB) | HTML Full-text | XML Full-text
Abstract
Recently, a noncentrosymmetric crystal, KNaNbOF5, has attracted attention due to its potential to present piezoelectric properties. Although α- and β-KNaNbOF5 are similar in their stoichiometries, their structural frameworks, and their synthetic routes, the two phases exhibit very different properties. This
[...] Read more.
Recently, a noncentrosymmetric crystal, KNaNbOF5, has attracted attention due to its potential to present piezoelectric properties. Although α- and β-KNaNbOF5 are similar in their stoichiometries, their structural frameworks, and their synthetic routes, the two phases exhibit very different properties. This paper presents, from first-principles calculations, comparative studies of the structural, electronic, piezoelectric, and elastic properties of the α and the β phase of the material. Based on the Christoffel equation, the slowness surface of the acoustic waves is obtained to describe its acoustic prosperities. These results may benefit further applications of KNaNbOF5. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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Open AccessFeature PaperArticle Functional Piezocrystal Characterisation under Varying Conditions
Materials 2015, 8(12), 8304-8326; doi:10.3390/ma8125456
Received: 29 September 2015 / Revised: 18 November 2015 / Accepted: 20 November 2015 / Published: 2 December 2015
Cited by 5 | PDF Full-text (4235 KB) | HTML Full-text | XML Full-text
Abstract
Piezocrystals, especially the relaxor-based ferroelectric crystals, have been subject to intense investigation and development within the past three decades, motivated by the performance advantages offered by their ultrahigh piezoelectric coefficients and higher electromechanical coupling coefficients than piezoceramics. Structural anisotropy of piezocrystals also provides
[...] Read more.
Piezocrystals, especially the relaxor-based ferroelectric crystals, have been subject to intense investigation and development within the past three decades, motivated by the performance advantages offered by their ultrahigh piezoelectric coefficients and higher electromechanical coupling coefficients than piezoceramics. Structural anisotropy of piezocrystals also provides opportunities for devices to operate in novel vibration modes, such as the d36 face shear mode, with domain engineering and special crystal cuts. These piezocrystal characteristics contribute to their potential usage in a wide range of low- and high-power ultrasound applications. In such applications, conventional piezoelectric materials are presently subject to varying mechanical stress/pressure, temperature and electric field conditions. However, as observed previously, piezocrystal properties are significantly affected by a single such condition or a combination of conditions. Laboratory characterisation of the piezocrystal properties under these conditions is therefore essential to fully understand these materials and to allow electroacoustic transducer design in realistic scenarios. This will help to establish the extent to which these high performance piezocrystals can replace conventional piezoceramics in demanding applications. However, such characterisation requires specific experimental arrangements, examples of which are reported here, along with relevant results. The measurements include high frequency-resolution impedance spectroscopy with the piezocrystal material under mechanical stress 0–60 MPa, temperature 20–200 °C, high electric AC drive and DC bias. A laser Doppler vibrometer and infrared thermal camera are also integrated into the measurement system for vibration mode shape scanning and thermal conditioning with high AC drive. Three generations of piezocrystal have been tested: (I) binary, PMN-PT; (II) ternary, PIN-PMN-PT; and (III) doped ternary, Mn:PIN-PMN-PT. Utilising resonant mode analysis, variations in elastic, dielectric and piezoelectric constants and coupling coefficients have been analysed, and tests with thermal conditioning have been carried out to assess the stability of the piezocrystals under high power conditions. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessFeature PaperArticle The Effect of Niobium Doping on the Electrical Properties of 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 Lead-Free Piezoelectric Ceramics
Materials 2015, 8(12), 8183-8194; doi:10.3390/ma8125457
Received: 1 October 2015 / Revised: 13 November 2015 / Accepted: 19 November 2015 / Published: 2 December 2015
Cited by 4 | PDF Full-text (4017 KB) | HTML Full-text | XML Full-text
Abstract
Ceramics in the system (Bi0.5K0.5)TiO3-BiFeO3 have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO3-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb)
[...] Read more.
Ceramics in the system (Bi0.5K0.5)TiO3-BiFeO3 have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO3-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb) is carried out to reduce the conductivity of (Bi0.5K0.5)TiO3-BiFeO3. Powders of composition 0.4(K0.5Bi0.5)Ti1−xNbxO3-0.6BiFe1−xNbxO3 (x = 0, 0.01 and 0.03) are prepared by the mixed oxide method and sintered at 1050 °C for 1 h. The effect of Nb doping on the structure is examined by X-ray diffraction. The microstructure is examined by scanning electron microscopy. The variation in relative permittivity with temperature is measured using an impedance analyzer. Ferroelectric properties are measured at room temperature using a Sawyer Tower circuit. Piezoelectric properties are measured using a d33 meter and a contact type displacement sensor. All the samples have high density, a rhombohedral unit cell and equiaxed, micron-sized grains. All the samples show relaxor-like behavior. Nb doping causes a reduction in conductivity by one to two orders of magnitude at 200 °C. The samples have narrow P-E loops reminiscent of a linear dielectric. The samples all possess bipolar butterfly S-E loops characteristic of a classic ferroelectric material. Nb doping causes a decrease in d33 and Smax/Emax. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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Open AccessFeature PaperArticle Growth and Characterization of Lead-free Piezoelectric Single Crystals
Materials 2015, 8(11), 7962-7978; doi:10.3390/ma8115436
Received: 15 September 2015 / Revised: 30 October 2015 / Accepted: 10 November 2015 / Published: 24 November 2015
Cited by 1 | PDF Full-text (4796 KB) | HTML Full-text | XML Full-text
Abstract
Lead-free piezoelectric materials attract more and more attention owing to the environmental toxicity of lead-containing materials. In this work, we review our first attempts of single crystal grown by the top-seeded solution growth method of BaTiO3 substituted with zirconium and calcium (BCTZ)
[...] Read more.
Lead-free piezoelectric materials attract more and more attention owing to the environmental toxicity of lead-containing materials. In this work, we review our first attempts of single crystal grown by the top-seeded solution growth method of BaTiO3 substituted with zirconium and calcium (BCTZ) and (K0.5Na0.5)NbO3 substituted with lithium, tantalum, and antimony (KNLSTN). The growth methodology is optimized in order to reach the best compositions where enhanced properties are expected. Chemical analysis and electrical characterizations are presented for both kinds of crystals. The compositionally-dependent electrical performance is investigated for a better understanding of the relationship between the composition and electrical properties. A cross-over from relaxor to ferroelectric state in BCTZ solid solution is evidenced similar to the one reported in ceramics. In KNLSTN single crystals, we observed a substantial evolution of the orthorhombic-to-tetragonal phase transition under minute composition changes. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessArticle Crystal Growth of Ca3Nb(Ga1−xAlx)3Si2O14 Piezoelectric Single Crystals with Various Al Concentrations
Materials 2015, 8(9), 5597-5605; doi:10.3390/ma8095264
Received: 2 June 2015 / Revised: 6 August 2015 / Accepted: 11 August 2015 / Published: 26 August 2015
Cited by 10 | PDF Full-text (2460 KB) | HTML Full-text | XML Full-text
Abstract
Ca3Nb(Ga1−xAlx)3Si2O14 (CNGAS) single crystals with various Al concentrations were grown by a micro-pulling-down (µ-PD) method and their crystal structures, chemical compositions, crystallinities were investigated. CNGAS crystals with x = 0.2, 0.4
[...] Read more.
Ca3Nb(Ga1−xAlx)3Si2O14 (CNGAS) single crystals with various Al concentrations were grown by a micro-pulling-down (µ-PD) method and their crystal structures, chemical compositions, crystallinities were investigated. CNGAS crystals with x = 0.2, 0.4 and 0.6 indicated a single phase of langasite-type structure without any secondary phases. In contrast, the crystals with x = 0.8 and 1 included some secondary phases in addition to the langasite-type phase. Lattice parameters, a- and c-axes lengths, of the langasite-type phase systematically decreased with an increase of Al concentration. The results of chemical composition analysis revealed that the actual Al concentrations in as-grown crystals were almost consistent with the nominal compositions. In addition, there was no large segregation of each cation along the growth direction. Full article
(This article belongs to the Special Issue Piezoelectric Materials)

Review

Jump to: Research

Open AccessFeature PaperReview Numerical Characterization of Piezoceramics Using Resonance Curves
Materials 2016, 9(2), 71; doi:10.3390/ma9020071
Received: 4 October 2015 / Revised: 15 December 2015 / Accepted: 18 December 2015 / Published: 27 January 2016
Cited by 1 | PDF Full-text (15542 KB) | HTML Full-text | XML Full-text
Abstract
Piezoelectric materials characterization is a challenging problem involving physical concepts, electrical and mechanical measurements and numerical optimization techniques. Piezoelectric ceramics such as Lead Zirconate Titanate (PZT) belong to the 6 mm symmetry class, which requires five elastic, three piezoelectric and two dielectric constants
[...] Read more.
Piezoelectric materials characterization is a challenging problem involving physical concepts, electrical and mechanical measurements and numerical optimization techniques. Piezoelectric ceramics such as Lead Zirconate Titanate (PZT) belong to the 6 mm symmetry class, which requires five elastic, three piezoelectric and two dielectric constants to fully represent the material properties. If losses are considered, the material properties can be represented by complex numbers. In this case, 20 independent material constants are required to obtain the full model. Several numerical methods have been used to adjust the theoretical models to the experimental results. The continuous improvement of the computer processing ability has allowed the use of a specific numerical method, the Finite Element Method (FEM), to iteratively solve the problem of finding the piezoelectric constants. This review presents the recent advances in the numerical characterization of 6 mm piezoelectric materials from experimental electrical impedance curves. The basic strategy consists in measuring the electrical impedance curve of a piezoelectric disk, and then combining the Finite Element Method with an iterative algorithm to find a set of material properties that minimizes the difference between the numerical impedance curve and the experimental one. Different methods to validate the results are also discussed. Examples of characterization of some common piezoelectric ceramics are presented to show the practical application of the described methods. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessFeature PaperReview Towards Lead-Free Piezoceramics: Facing a Synthesis Challenge
Materials 2016, 9(1), 21; doi:10.3390/ma9010021
Received: 30 October 2015 / Revised: 27 November 2015 / Accepted: 17 December 2015 / Published: 2 January 2016
Cited by 15 | PDF Full-text (5158 KB) | HTML Full-text | XML Full-text
Abstract
The search for electroceramic materials with enhanced ferro-pyro-piezoelectric properties and revealing the perovskite type structure has been the objective of a significant number of manuscripts reported in the literature. This has been usually carried out by proposing the synthesis and processing of new
[...] Read more.
The search for electroceramic materials with enhanced ferro-pyro-piezoelectric properties and revealing the perovskite type structure has been the objective of a significant number of manuscripts reported in the literature. This has been usually carried out by proposing the synthesis and processing of new compounds and solid solution series. In this work, several methods to obtain ferro-pyro-piezoelectric families of materials featuring the well-known ABO3 perovskite structure (or related) such as BaTiO3, Ba1–xCaxTi1–yZryO3, (Bi0.5Na0.5)TiO3, (K0.5Na0.5)NbO3 and their solid solutions with different cations either in the A or B positions, are presented. For this kind of materials, the challenge for obtaining a single phase compound with a specific grain size and morphology and, most importantly, with the adequate stoichiometry, will also be discussed. The results reviewed herein will be discussed in terms of the tendency of working with softer conditions, i.e., lower temperature and shorter reaction times, also referred to as soft-chemistry. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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Open AccessFeature PaperReview Ferroelectrics under the Synchrotron Light: A Review
Materials 2016, 9(1), 14; doi:10.3390/ma9010014
Received: 31 October 2015 / Revised: 14 December 2015 / Accepted: 23 December 2015 / Published: 30 December 2015
Cited by 2 | PDF Full-text (10453 KB) | HTML Full-text | XML Full-text
Abstract
Currently, an intensive search for high-performance lead-free ferroelectric materials is taking place. ABO3 perovskites (A = Ba, Bi, Ca, K and Na; B = Fe, Nb, Ti, and Zr) appear as promising candidates. Understanding the structure–function relationship is mandatory, and, in this
[...] Read more.
Currently, an intensive search for high-performance lead-free ferroelectric materials is taking place. ABO3 perovskites (A = Ba, Bi, Ca, K and Na; B = Fe, Nb, Ti, and Zr) appear as promising candidates. Understanding the structure–function relationship is mandatory, and, in this field, the roles of long- and short-range crystal orders and interactions are decisive. In this review, recent advances in the global and local characterization of ferroelectric materials by synchrotron light diffraction, scattering and absorption are analyzed. Single- and poly-crystal synchrotron diffraction studies allow high-resolution investigations regarding the long-range average position of ions and subtle global symmetry break-downs. Ferroelectric materials, under the action of electric fields, undergo crystal symmetry, crystallite/domain orientation distribution and strain condition transformations. Methodological aspects of monitoring these processes are discussed. Two-dimensional diffraction clarify larger scale ordering: polycrystal texture is measured from the intensities distribution along the Debye rings. Local order is investigated by diffuse scattering (DS) and X-ray absorption fine structure (XAFS) experiments. DS provides information about thermal, chemical and displacive low-dimensional disorders. XAFS investigation of ferroelectrics reveals local B-cation off-centering and oxidation state. This technique has the advantage of being element-selective. Representative reports of the mentioned studies are described. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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Open AccessFeature PaperReview Bismuth Sodium Titanate Based Materials for Piezoelectric Actuators
Materials 2015, 8(12), 8467-8495; doi:10.3390/ma8125469
Received: 19 October 2015 / Revised: 13 November 2015 / Accepted: 23 November 2015 / Published: 4 December 2015
Cited by 20 | PDF Full-text (5759 KB) | HTML Full-text | XML Full-text
Abstract
The ban of lead in many electronic products and the expectation that, sooner or later, this ban will include the currently exempt piezoelectric ceramics based on Lead-Zirconate-Titanate has motivated many research groups to look for lead-free substitutes. After a short overview on different
[...] Read more.
The ban of lead in many electronic products and the expectation that, sooner or later, this ban will include the currently exempt piezoelectric ceramics based on Lead-Zirconate-Titanate has motivated many research groups to look for lead-free substitutes. After a short overview on different classes of lead-free piezoelectric ceramics with large strain, this review will focus on Bismuth-Sodium-Titanate and its solid solutions. These compounds exhibit extraordinarily high strain, due to a field induced phase transition, which makes them attractive for actuator applications. The structural features of these materials and the origin of the field-induced strain will be revised. Technologies for texturing, which increases the useable strain, will be introduced. Finally, the features that are relevant for the application of these materials in a multilayer design will be summarized. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessFeature PaperReview Elastic Properties and Enhanced Piezoelectric Response at Morphotropic Phase Boundaries
Materials 2015, 8(12), 8195-8245; doi:10.3390/ma8125452
Received: 2 October 2015 / Revised: 13 November 2015 / Accepted: 18 November 2015 / Published: 2 December 2015
Cited by 11 | PDF Full-text (1973 KB) | HTML Full-text | XML Full-text
Abstract
The search for improved piezoelectric materials is based on the morphotropic phase boundaries (MPB) between ferroelectric phases with different crystal symmetry and available directions for the spontaneous polarization. Such regions of the composition x − T phase diagrams provide the conditions for minimal
[...] Read more.
The search for improved piezoelectric materials is based on the morphotropic phase boundaries (MPB) between ferroelectric phases with different crystal symmetry and available directions for the spontaneous polarization. Such regions of the composition x − T phase diagrams provide the conditions for minimal anisotropy with respect to the direction of the polarization, so that the polarization can easily rotate maintaining a substantial magnitude, while the near verticality of the TMPB(x) boundary extends the temperature range of the resulting enhanced piezoelectricity. Another consequence of the quasi-isotropy of the free energy is a reduction of the domain walls energies, with consequent formation of domain structures down to nanoscale. Disentangling the extrinsic and intrinsic contributions to the piezoelectricity in such conditions requires a high level of sophistication from the techniques and analyses for studying the structural, ferroelectric and dielectric properties. The elastic characterization is extremely useful in clarifying the phenomenology and mechanisms related to ferroelectric MPBs. The relationship between dielectric, elastic and piezoelectric responses is introduced in terms of relaxation of defects with electric dipole and elastic quadrupole, and extended to the response near phase transitions in the framework of the Landau theory. An account is provided of the anelastic experiments, from torsional pendulum to Brillouin scattering, that provided new important information on ferroelectric MPBs, including PZT, PMN-PT, NBT-BT, BCTZ, and KNN-based systems. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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Open AccessFeature PaperReview Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics
Materials 2015, 8(12), 8117-8146; doi:10.3390/ma8125449
Received: 16 October 2015 / Revised: 16 November 2015 / Accepted: 20 November 2015 / Published: 1 December 2015
Cited by 33 | PDF Full-text (8599 KB) | HTML Full-text | XML Full-text
Abstract
The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining
[...] Read more.
The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na)/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions) and different atmospheres (i.e., defect chemistry) on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT). Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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Open AccessFeature PaperReview Anti-Ferroelectric Ceramics for High Energy Density Capacitors
Materials 2015, 8(12), 8009-8031; doi:10.3390/ma8125439
Received: 29 September 2015 / Revised: 2 November 2015 / Accepted: 11 November 2015 / Published: 25 November 2015
Cited by 26 | PDF Full-text (3361 KB) | HTML Full-text | XML Full-text
Abstract
With an ever increasing dependence on electrical energy for powering modern equipment and electronics, research is focused on the development of efficient methods for the generation, storage and distribution of electrical power. In this regard, the development of suitable dielectric based solid-state capacitors
[...] Read more.
With an ever increasing dependence on electrical energy for powering modern equipment and electronics, research is focused on the development of efficient methods for the generation, storage and distribution of electrical power. In this regard, the development of suitable dielectric based solid-state capacitors will play a key role in revolutionizing modern day electronic and electrical devices. Among the popular dielectric materials, anti-ferroelectrics (AFE) display evidence of being a strong contender for future ceramic capacitors. AFE materials possess low dielectric loss, low coercive field, low remnant polarization, high energy density, high material efficiency, and fast discharge rates; all of these characteristics makes AFE materials a lucrative research direction. However, despite the evident advantages, there have only been limited attempts to develop this area. This article attempts to provide a focus to this area by presenting a timely review on the topic, on the relevant scientific advancements that have been made with respect to utilization and development of anti-ferroelectric materials for electric energy storage applications. The article begins with a general introduction discussing the need for high energy density capacitors, the present solutions being used to address this problem, and a brief discussion of various advantages of anti-ferroelectric materials for high energy storage applications. This is followed by a general description of anti-ferroelectricity and important anti-ferroelectric materials. The remainder of the paper is divided into two subsections, the first of which presents various physical routes for enhancing the energy storage density while the latter section describes chemical routes for enhanced storage density. This is followed by conclusions and future prospects and challenges which need to be addressed in this particular field. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessFeature PaperReview Extrinsic Contribution and Instability Properties in Lead-Based and Lead-Free Piezoceramics
Materials 2015, 8(11), 7821-7836; doi:10.3390/ma8115426
Received: 19 October 2015 / Revised: 11 November 2015 / Accepted: 13 November 2015 / Published: 19 November 2015
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Abstract
Piezoceramic materials generally exhibit a notable instability of their functional properties when they work under real external conditions. This undesirable effect, known as nonlinear behavior, is mostly associated with the extrinsic contribution to material response. In this article, the role of the ferroelectric
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Piezoceramic materials generally exhibit a notable instability of their functional properties when they work under real external conditions. This undesirable effect, known as nonlinear behavior, is mostly associated with the extrinsic contribution to material response. In this article, the role of the ferroelectric domain walls’ motion in the nonlinear response in the most workable lead-based and lead-free piezoceramics is reviewed. Initially, the extrinsic origin of the nonlinear response is discussed in terms of the temperature dependence of material response. The influence of the crystallographic phase and of the phase boundaries on the material response are then reviewed. Subsequently, the impact of the defects created by doping in order to control the extrinsic contribution is discussed as a way of tuning material properties. Finally, some aspects related to the grain-size effect on the nonlinear response of piezoceramics are surveyed. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
Open AccessFeature PaperReview Potassium Sodium Niobate-Based Lead-Free Piezoelectric Multilayer Ceramics Co-Fired with Nickel Electrodes
Materials 2015, 8(11), 7423-7438; doi:10.3390/ma8115389
Received: 29 September 2015 / Revised: 26 October 2015 / Accepted: 28 October 2015 / Published: 3 November 2015
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Abstract
Although lead-free piezoelectric ceramics have been extensively studied, many problems must still be overcome before they are suitable for practical use. One of the main problems is fabricating a multilayer structure, and one solution attracting growing interest is the use of lead-free multilayer
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Although lead-free piezoelectric ceramics have been extensively studied, many problems must still be overcome before they are suitable for practical use. One of the main problems is fabricating a multilayer structure, and one solution attracting growing interest is the use of lead-free multilayer piezoelectric ceramics. The paper reviews work that has been done by the authors on lead-free alkali niobate-based multilayer piezoelectric ceramics co-fired with nickel inner electrodes. Nickel inner electrodes have many advantages, such as high electromigration resistance, high interfacial strength with ceramics, and greater cost effectiveness than silver palladium inner electrodes. However, widely used lead zirconate titanate-based ceramics cannot be co-fired with nickel inner electrodes, and silver palladium inner electrodes are usually used for lead zirconate titanate-based piezoelectric ceramics. A possible alternative is lead-free ceramics co-fired with nickel inner electrodes. We have thus been developing lead-free alkali niobate-based multilayer ceramics co-fired with nickel inner electrodes. The normalized electric-field-induced thickness strain (Smax/Emax) of a representative alkali niobate-based multilayer ceramic structure with nickel inner electrodes was 360 pm/V, where Smax denotes the maximum strain and Emax denotes the maximum electric field. This value is about half that for the lead zirconate titanate-based ceramics that are widely used. However, a comparable value can be obtained by stacking more ceramic layers with smaller thicknesses. In the paper, the compositional design and process used to co-fire lead-free ceramics with nickel inner electrodes are introduced, and their piezoelectric properties and reliabilities are shown. Recent advances are introduced, and future development is discussed. Full article
(This article belongs to the Special Issue Piezoelectric Materials)
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