Nanocrystal BaTiO3: Pressure-induced transformation from mixed ionic–electronic to pure electronic cyclic conduction

Abstract

The electrical transport characteristics of nano-barium titanate (BaTiO3) were systematically investigated under high pressures up to 35.64 GPa using AC impedance spectroscopy measurements and first-principles calculations. Impedance spectroscopy measurements provide insights into the conduction mechanism involving pressure-induced transformation from mixed ionic–electronic to pure electronic cyclic conduction. Through first-principles calculations, we have elucidated the underlying physical mechanisms responsible for the emergence of transformation from mixed ionic–electronic to pure electronic cyclic conduction. This phenomenon arises from variations in C-axis compressibility and phase transition from tetragonal to cubic phase, resulting in abrupt changes in electron density around oxygen atoms. These discontinuous changes are accompanied by alterations in initial resistance (R), relaxation frequency (F), and dielectric constant. By applying pressure, it becomes possible to effectively control the lattice spacing, thereby manipulating the charge density of OII ions and facilitating a seamless transition between mixed ionic–electronic and pure electronic conduction pathways. Pressure modulation also regulates the migration behavior of O2− ions, leading to an enhancement in the conductivity of nano-BaTiO3 materials. This study contributes to advancing our understanding of the transformation from mixed ionic–electronic to pure electronic cyclic conduction occurring within solid electrolytes.