Effects of A-Site (NaCe) Substitution with Na-Deficiency on Structures and Properties of CaBi₄Ti₄O₁₅-Based High-Curie-Temperature Ceramics

Three kinds of bismuth-layer-structured ferroelectric (BLSF) ceramics, CaBi₄Ti₄O₁₅ (CBT), Ca_0.8(CeNa)_0.1Bi₄Ti₄O₁₅ (CNBT), and Na-deficient Ca_0.8(Ce_0.1Na_0.05\Box_0.05)Bi₄Ti₄O₁₅ [CN\BoxBT] (where \Box represents vacancies) were prepared by a conventional ceramic technique. X-ray powder diffraction showed that their crystal structures are a single phase of BLSF with m=4. Sintering characteristics of the three ceramics were also discussed. Scanning electron microscope (SEM) micrographs of CN\BoxBT showed that the grain is platelike. The A-site (NaCe) substitution can improve the piezoelectric constant d₃₃ and high-temperature resistivity with decreasing Curie temperature. The modification by A-site (NaCe) substitution with Na-deficiency is more pronounced than CNBT, which not only leads to a very high piezoelectric constant d₃₃ and high-temperature resistivity but also increases the Curie temperature. The reason for the high T_c (T_c=866°C) of CN\BoxBT is considered to be internal stress. As a result, Na-deficient CN\BoxBT ceramic is found to be an excellent high-temperature piezoelectric material.