High piezoelectricity by multiphase coexisting point: Barium titanate derivatives
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troduction Barium titanate (BaTiO3 [BT]) was discovered in the 1940s during World War II.1 Before the emergence of Pb(Zr,Ti) O3 (PZT) in the late 1950s, BT had been the most important known piezoelectric material due to its piezoelectric coefficient (induced polarization per unit stress applied to the material) d33 = 120–190 pC/N, which is significantly higher than that of older piezoelectric materials such as triglycine sulfate (TGS), potassium dihydrogen phosphate (KDP), and quartz. However, compared to PZT, which shows outstanding piezoelectricity with d33 = 300–600 pC/N, BT and BT-based materials appeared to be “mediocre” in terms of both piezoelectricity and TC (Curie temperature, approximately 130°C). Thus, they were soon replaced by PZT in piezoelectric applications.2 It should be noted that although pure BT can show higher piezoelectricity in some special forms such as single crystals,3,4 textured polycrystals,5 or fine-grain/domain ceramics,6,7 it is challenging to achieve PZT-like, intrinsically high piezoelectricity in simple chemically modified BT-based ceramics. The Pb-free surge over the past 20 years has revived significant research on the piezoelectricity of BT-based materials,
in an attempt to discover a BT-based ceramic that is comparable to PZT in piezoelectric characteristics.3–9 In 2009, Liu and Ren reported large piezoelectric response for the Ba(Zr,Ti)O3(Ba,Ca)TiO3 (BZT-BCT) ceramic system with a d33 coefficient larger than 600 pC/N, which is comparable to soft PZT ceramics with high sensitivity and permittivity.10 These ceramics are made by a standard solid-state reaction method and are random polycrystals, suggesting that the high piezoelectricity stems from its inherent effect. Further studies have shown that similar values of high piezoelectricity are also present in a generic class of BT-based materials, including Ba(Sn,Ti)O3(Ba,Ca)TiO3 (BTS-BCT) and Ba(Hf,Ti)O3-(Ba,Ca)TiO3 (BHT-BCT).11,12 In contrast to the mediocre piezoelectricity of BT-based ceramics reported over the past 60 years, such soft-PZT-like piezoelectricity in BT-based ceramics came as a surprise to the piezoelectric community, as it can be a potential replacement for Pb-based piezoelectric materials. Significant efforts have thus been made toward understanding and explaining this phenomenon.13–29 In the following, we provide a brief review of the state-of-the-art key results and our current understanding. A more comprehensive review can be found in Reference 30.
Jinghui Gao, State Key Laboratory of Electrical Insulation and Power Equipment and Multidisciplinary Materials Research Center, Frontier Institute of Science and Technology, Xi’an Jiaotong University, China; [email protected] Xiaoqin Ke, Frontier Institute of Science and Technology and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, China; [email protected] Matias Acosta, University of Cambridge, UK; [email protected] Julia Glaum, Department of Materials Science and Engineering, Norwegian University of Science and
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