Pressure-Induced Cyclic Transformation of Ion–Electron in Nanocrystal SrTiO₃

The electrical transport properties of nano SrTiO3 were systematically investigated under high pressures up to 24.5 GPa using AC impedance spectroscopy and first-principles calculations. Through these methods, we identified and elucidated the underlying physical mechanisms responsible for the cyclic ion–electron transformation. This phenomenon arises from variations in C-axis compressibility and a phase transition from the cubic to tetragonal structure, which induces abrupt changes in electron density around oxygen atoms. By applying pressure, it becomes possible to control the lattice spacing, thereby modulating the charge density of O ions and enabling a smooth transition between ion and electron conduction pathways. This study deepens our understanding of the cyclic transformation of ion–electron behavior within solid electrolytes.