Structural evidence for the polymorphic phase boundary in (Na,K)NbO3 based perovskites close to the rhombohedral-tetragonal phase coexistence zone
Structural evidence for the polymorphic phase boundary in (Na,K)NbO3 based perovskites close to the rhombohedral-tetragonal phase coexistence zone
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DOI：
10.1016/j.actamat.2020.06.002
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发表时间：
2020-08-15
期刊：
影响因子：
9.4
通讯作者：
Zuo, Ruzhong
中科院分区：
文献类型：
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作者：
Fu, Jian;Zuo, Ruzhong
多相共存是高性能压电陶瓷中一个重要的技术概念，因为它能够获得极高的机电性能。然而，事实上，它并不总是产生与器件应用相关的小场压电性能的理想热稳定性。本工作以(Na0.52K0.4)(Nb0.84Sb0.08)O-3-0.055LiTaO(3)-0.025BaZrO(3)为例，采用X-射线衍射仪、Rietveld结构修正和变温电学测量等手段，研究了一种典型的无铅室温压电组分：三方相(R)和四方相(T)共存。这种精细的晶体结构在初始状态是R、正交(O)和T的三相共存，而在极化状态由于电场诱导不可逆的O-Mc相变而演化为R+单斜晶系(M-C)+T相共存。特别是，只要退火温度低于居里温度，场致M-C相就可以稳定地存在并保持其浓度。一个有趣的发现是，极化后的样品仍然保持其原始状态的相变多态，表现为温度驱动的R-O(M-C)-T相变，导致热循环后的压电系数严重退化，这不仅是由于M-C相的磁畴去织构，而且在重复相变过程中R和T相也是如此。本研究将有助于理解R-T共存的(Na，K)NbO_3系无铅固溶体陶瓷中多晶型相界的本质和压电性随温度变化的结构来源。(C)2020 Acta Materialia Inc.由爱思唯尔有限公司出版。版权所有。
The multi-phase coexistence is a technologically important concept in high-performance piezoelectric ceramics owing to the ability of achieving extremely increased electromechanical properties. However, in fact it cannot always produce desirable thermal stability of small-field piezoelectric properties relevant to the device application. In this work, a typical lead-free piezoelectric composition of (Na0.52K0.4)(Nb0.84Sb0.08)O-3-0.055LiTaO(3)-0.025BaZrO(3) coexisted with rhombohedral (R) and tetragonal (T) phases at room temperature was investigated as a case study by means of ex/in-situ synchrotron x-ray diffraction, Rietveld structure refinement and measurements of temperature-dependent electrical properties. The refined crystal structure proves to be a three-phase coexistence of R, orthorhombic (O) and T at virgin state, and evolves into the R+monoclinic (M-C)+T phase coexistence at poled state owing to an electric field induced irreversible O-Mc phase transition. Particularly, the field induced M-C phase can stably exist and maintain its concentration as long as the annealing temperature is below the Curie temperature. An interesting finding is that the poled sample still retains the polymorphism of phase transition like its virgin state featuring the temperature driven R-O(M-C)-T phase transition, leading to seriously degraded piezoelectric coefficients after thermal cycles due to domain de-texturing of not only M-C phase, but also R and T phases during repeated phase transition. The present study would benefit to understanding of the nature of polymorphic phase boundary and the structure origin of temperature-dependent piezoelectric properties in R-T coexisted (Na,K)NbO3-based lead-free solid-solution ceramics. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.