Hydrostatic Piezoelectric Coefficient d h of PZT Ceramics and PZN-PT and PYN-PT Single Crystals

The hydrostatic piezoelectric coefficient d_h of Pb(Zr_xTi_{1 – x})O₃ ceramics (PZT), and of Pb(Zn_1/3Nb_{2/ 3})O₃-PbTiO₃ and Pb(Yb_1/2Nb_1/2)O₃-PbTiO₃ (PZN-PT, PYN-PT, respectively) single crystals with compositions near to the morphotropic phase boundary (MPB) have been measured using a dynamic hydrostatic method. The effects of DC electric field and static component of hydrostatic stress on d_h of PZT ceramics, PZN-PT and PYN-PT single crystals were studied. Changes of the piezoelectric hydrostatic coefficients d_h caused by an electric field (DC bias) were observed along with pressure and temperature dependencies. The measurement of the hydrostatic piezoelectric coefficient d_h seems to be promising for investigation of intrinsic (single domain) and extrinsic (domain-walls) contributions to piezoelectric behavior of single crystals and ceramic materials.     

RELAXATIONAL PROPERTIES OF LAYERED FERROELECTRICS CaBi1.5 La0.5Nb2O9

ABSTRACT

CaBi_1.5La_0.5Nb₂O₉ ceramics were prepared by a conventional solid-state reaction method. Their structure and dielectric properties were investigated. X-ray diffraction analysis indicated that single phase layered perovskites were obtained. Dielectric studies demonstrated that CaBi_1.5La_0.5Nb₂O₉ is characteristic of relaxor ferroelectrics. The dielectric relaxation of CaBi_1.5La_0.5Nb₂O₉ was modeled using the Vögel-Fulcher relationship, and the dielectric relaxation in CaBi_1.5La_0.5Nb₂O₉ is found to be analogous to a spin glass with thermally activated polarization fluctuations above a static freezing temperature.     

Bi-modified SrTiO3-based ceramics for high-temperature energy storage applications

Dielectric capacitors with high energy storage performance are in great demand for emerging advanced energy storage applications. Relaxor ferroelectrics are one type dielectric materials possessing high energy storage density and energy efficiency simultaneously. In this study, 0.9(Sr_0.7Bi_0.2)TiO₃–0.1Bi(Mg_0.5Me_0.5)O₃ (Me = Ti, Zr, and Hf) dielectric relaxors are designed and the corresponding energy storage properties are investigated. The excellent recoverable energy density of 3.1 J/cm³ with a high energy efficiency of 93% is achieved at applied electric field of 360 kV/cm for 0.9(Sr_0.7Bi_0.2)TiO₃–0.1Bi(Mg_0.5Hf_0.5)O₃ (0.9SBT–0.1BMH) ceramic. High breakdown strength of 460 kV/cm in 0.9SBT–0.1BMH ceramic is obtained by Weibull distribution with satisfied reliability. In addition, 0.9SBT–0.1BMH shows outstanding thermal stability of energy storage performance up to 200°C, with the variation being less than 5%, together with satisfying cycling stability and high charge-discharge rate, making the 0.9SBT–0.1BMH ceramic a potential lead-free candidate for high power energy storage applications at elevated temperature.     

铋掺杂铌镁酸铅陶瓷的制备及其有序现象研究

采用二步固相合成法制备钙钛矿相的掺铋铌镁酸铅陶瓷,利用ＸＲＤ和ＴＥＭ选区电子衍射技术对Ｂ位离子非计量有序排列结构进行了表征．研究表明,当为施主掺杂而提高Ｍｇ^２＋、Ｎｂ^５＋离子比例时,铌酸镁前驱体中逐渐出现六方Ｍｇ_４Ｎｂ_９Ｏ_６相．施主Ｂｉ^３＋离子能够有效促进有序微区长大,提高系统有序度．利用Ｘ射线衍射线宽法对ＸＲＤ慢扫描谱进行处理,求得当掺入５％Ｂｉ^３＋离子时,有序微区平均尺寸由纯ＰＭＮ的５nｍ提高到２２ｎｍ．     

Single-Calcination Synthesis of Pyrochlore-Free 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 and Pb(Mg1/3Nb2/3)O3 Ceramics Using a Coating Method

A coating approach for synthesizing 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (0.9PMN–0.1PT) and PMN using a single calcination step was demonstrated. The pyrochlore phase was prevented by coating Mg(OH)₂ on Nb₂O₅ particles. Coating of Mg(OH)₂ on Nb₂O₅ was done by precipitating Mg(OH)₂ in an aqueous Nb₂O₅ suspension at pH 10. The coating was confirmed using optical micrographs and zeta-potential measurements. A single calcination treatment of the Mg(OH)₂-coated Nb₂O₅ particles mixed with appropriate amounts of PbO and PbTiO₃ powders at 900°C for 2 h produced pyrochlore-free perovskite 0.9PMN–0.1PT and PMN powders. The elimination of the pyrochlore phase was attributed to the separation of PbO and Nb₂O₅ by the Mg(OH)₂ coating. The Mg(OH)₂ coating on the Nb₂O₅ improved the mixing of Mg(OH)₂ and Nb₂O₅ and decreased the temperature for complete columbite conversion to ∼850°C. The pyrochlore-free perovskite 0.9PMN–0.1PT powders were sintered to 97% density at 1150°C. The sintered 0.9PMN–0.1PT ceramics exhibited a dielectric constant maximum of ∼24 660 at 45°C at a frequency of 1 kHz.     

Giant Polarization in Quasi-Adiabatic Ferroelectric Na+ Electrolyte for Solid-State Energy Harvesting and Storage

The advent of new solid-state energy storage devices to tackle the electrical revolution requires the usage of nonlinear behavior leading to emergent phenomena. The ferroelectric analyzed herein belongs to a family of electrolytes that allow energy harvesting and storage as part of its self-charging features when thermally activated. The Na_2.99Ba_0.005ClO electrolyte shows quasi-adiabatic behavior with a continuous increase in polarization upon cycling, displaying almost no hysteresis. The maximum polarization obtained at a weak electric field is giant and similar to the remanent polarization. It depends on the temperature with a pyroelectric coefficient of 5.37 C m⁻² °C⁻¹ from −5 to 46 °C. The emergence occurs via negative resistance and capacitance. The glass transition is found to have its origins in the sharp depolarization at 46 – 48 °C. Above –10 °C, at ≈ –5 °C, another thermal anomaly may rely on the topologic characteristics of the A_3–2xBa_xClO (A = Li, Na, K) glass electrolytes enabling positive feedback of the current of electrons throughout the surface of the inner cell. The phenomena may pave the way toward a better understanding of dipolar nanodomain fragile glasses with exceptional ferroelectric characteristics to architect energy harvesting and storage devices based on multivalent thermally activated Na⁺-ion-ion electrolytes.     

Anisotropy free energy contribution of the ferroelectric domain dynamics in PMN-PT and PIN-PMN-PT relaxor ferroelectrics

A direct correlation between the materials property behavior with its associated ferroelectric domain mechanisms and the anisotropic component of the Landau free energy is established for binary PMN-PT (generation I) and ternary PIN-PMN-PT (generation II) relaxor ferroelectric single crystal material systems. In addition to their trade-off in material properties, the observed ferroelectric domain dynamic and the determined free energy anisotropies, especially as approaching phase transition, provide direct insights into the materials field-dependent behavior between the binary and ternary ferroelectric systems. Domain configuration features such as lamellar structures in binary PMN-PT and concentric oval-like structures in ternary PIN-PMN-PT result in different material responses to external stimuli. Compared to binary PMN-PT, the concentric oval-like domain structures of ternary PIN-PMN-PT result in a 20°C higher temperature range of field-dependent linear behavior, 40% increase in coercive electric field $E_C,$ higher elastic stiffness during ferroelectric domain switching, and lower electromechanical energy losses. Separation of the isotropic and anisotropic components in the Landau free energy reveals a higher anisotropic free energy contribution from the ternary system, especially at temperature for practical applications. The high anisotropic free energy found in the ternary PIN-PMN-PT system implies that the concentric oval-like domain structure contributes to reduced electromechanical energy losses and enhanced stability under external applied fields.