Pressure-induced ionic–polaronic–ionic transition in LaAlO3

Abstract

Combining alternate-current impedance spectrum measurement and first-principle calculations, we thoroughly analyzed the electrical transport behavior of LaAlO3 under high pressure. A pressure-induced ionic–polaronic–ionic transition has been discovered through impedance spectroscopy measurements. Through first-principle calculations, we have elucidated the physical origin of the emergence of polaronic conduction, which results from the distortion of electron density background around Al and O atoms. Furthermore, the discontinuous changes in the starting frequency of ion migration fW, relaxation frequency fb, and ionic resistance Ri have been found at around 13.2 GPa, which can be ascribed to the phase transition of LaAlO3 from rhombohedral to cubic phase. Pressure can enhance the migration of O2− ions, causing an increase in the ionic conductivity of LaAlO3. This research will deepen our comprehension on the ion migration in solid electrolytes.