HU Hao, JIANG Xiangping, CHEN Chao, TU Na, CHEN Yunjing, HUANG Xiaokun, NIE Xin, LIU Fang, SU Chunyang, ZHUANG Junsheng

(Jiangxi Key Laboratory of Advanced Ceramic Materials, School of Material Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333001, Jiangxi, China)

Abstract: Bismuth layer-structured piezoelectric ceramics play an important role in the field of high temperature electronic devices, whose conduction and relaxation mechanism at high temperatures directly influence their electrical properties. The internal defects of Na_0.5Bi_8.5Ti₇O₂₇ inter-growth bismuth layer-structured lead-free piezoelectric ceramics synthesized with solid-state reactions and the intrinsic connection between the conduction and relaxation mechanism have been systematically studied by using X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS) and impedance spectra. It was found that the ceramic samples possessed a single bismuth layer-structure with a trace of Ti³⁺ in the lattice. According to impedance analytic results, the conduction mechanism of the samples in the temperature range of 400-620 ℃ was closely linked to the first ionization of oxygen vacancies with a DC conductivity activation energy of 1.11 eV. However, the relaxation in the above temperature range followed two mechanisms, corresponding to short range transition of oxygen vacancies and valence change of titanium ions, in the temperature regions of 400-540 ℃ and 540-620 ℃, with relaxation activation energies of 1.12 eV and 0.73 eV, respectively.
Key words: piezoelectric ceramics; Na_0.5Bi_8.5Ti₇O₂₇; conduction mechanism; relaxation mechanism