Hydrostatic Pressure Induced Structural Instability And Dielectric Property Of Cubic Bazro_3

摘要

Using the first-principle calculations, we investigate in detail the structure instability resulting from softening of the polar zone-center phonon mode [ferroelectric (FE) instability] and nonpolar zone-boundary mode [antiferrodistortive (AFD) instability] in cubic BaZrO_3 (BZO) under hydrostatic pressure P from -20 to 90 GPa. The hydrostatic pressure enhances the AFD instability, while it suppresses and then enhances the FE instability. A sequence of FE→cubic→AFD → AFD/FE phase transitions with increasing P is predicted. A careful examination of the pressure dependence of full phonon dispersions and interatomic force constants in real space reveals the microscopic key interactions in driving the transitions. With increasing pressure P, the drastically evolving short-range forces suppress the FE instability induced by the long-range dipole-dipole forces under low pressure, and enhance both the AFD and FE instability under high pressure. We investigate the dielectric properties of cubic BZO under hydrostatic pressure. The dielectric constant as a function of pressure shows a minimum contributed from the TO_1 mode with the lowest frequency. We argue that this pressure dependence of the dielectric constant mainly originates from fluctuations of the SR forces.