The origin of weak coupling between polar clusters in Ta₂O₅-doped 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃

¹ Guangxi Key Lab of Optical and Electronic Functional Materials and Devices, College of Materials Science and Engineering, Guilin University of Technology - Guilin 541004, China
² College of Energy and Building Environment, Guilin University of Aerospace Technology - Guilin 541000, Guangxi, China
³ College of Mechanical and Electronic Engineering, Jiangxi College of Applied Technology - Ganzhou, 341004, Jiangxi, China

^(a) ljliu2@163.com

Received: 10 November 2019
Accepted: 12 February 2020

Abstract

Ta₂O₅-doped 0.94Bi_0.5Na_0.5 TiO₃-0.06BaTiO₃ [()(0.94BNT-0.06BT)-xTa ()] ceramics were prepared by a solid-state reaction technique. The single perovskite structure with space group R3c of the ceramics was identified by X-ray diffraction (XRD). Raman spectroscopy revealed the evolution of the local structure with Ta₂O₅ concentration. The temperature dependence of dielectric permittivity of the ceramics were deconvoluted by three Gaussian distribution functions which suggests that three dielectric anomalies exist in this system. The low-temperature dielectric anomaly exhibits a typical relaxor behavior with strong frequency dispersion (reentrant relaxor behavior). The activation energy derived from the V-F law is 0.298 eV, 0.338 eV, 0.412 eV and 0.449 eV, for , 0.005, 0.01 and 0.02, respectively. The mid-temperature and high-temperature anomalies are attributed to two structure phase transitions. The increase of the activation energies suggests that the coupling between polar clusters or polar nanoregions (PNRs) becomes weaker. The origin of the interaction between PNRs and phase transition behavior has been proposed according to the average structure, local structure and defect compensation mechanism of the system.