Dielectric properties are one of the important attributes of materials, whose enhancement is of significant importance for practical applications. In this work, the dielectric properties of HfO2 were studied under high pressure by combining in situ Raman scattering, alternating-current (AC) impedance spectroscopy measurements, and differential charge density calculations. It was found that HfO2 undergoes pressure-induced irreversible phase transitions from P21/c to Pbca and then to the Pnma structure, and its high-pressure Pnma structure can be retained at atmospheric pressure. AC impedance spectroscopy measurements revealed that the relative permittivity of HfO2 has not only been increased by approximately 3 times after a cycle of compression and decompression but also the dielectric loss factor has been dramatically decreased, indicating that an obvious enhancement of dielectric performance has been obtained. Differential charge density calculations suggested that a large number of electrons transferred from Hf4+ cations to O2– anions could be the physical origin of the increase of electric dipole moments in HfO2 and the enhancement of dielectric properties.
Cao et al. (Thu,) studied this question.