Pressure-Directed Mixed Ionic–Electronic to Pure Electronic Conduction Transition and Improved Dielectric Properties in Nanocrystalline BaTiO ₃

As a typical dielectric ceramic material, BaTiO₃ has attracted considerable interest owing to its high dielectric constant. Using a combination of high-pressure AC impedance spectroscopy, Raman spectroscopy, and theoretical calculations, this study investigated the structural and electrical properties of nanocrystalline BaTiO₃ at pressures of up to 30 GPa. The material underwent two phase transitions: from a mixed orthorhombic/tetragonal phase to a pure tetragonal phase and finally to a cubic phase. The superior dielectric constant of the tetragonal phase, compared to that of the other two phases, results from the rapid polarization switching of its 180° domains. The phase transition from the tetragonal phase to the cubic phase leads to a transformation from mixed ionic-electronic conduction to pure electronic conduction, as the high migration energy barrier in the cubic phase hinders ionic conduction. This work demonstrates that applying pressure is a feasible strategy to enhance the dielectric performance of BaTiO₃-type dielectrics.