Pressure-Enhanced Dielectric Performance in HfO₂

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 O^2- anions could be the physical origin of the increase of electric dipole moments in HfO₂ and the enhancement of dielectric properties.