Hybrid improper ferroelectricity and pressure-induced enhancement of polarization in Ba3Ce2O7 predicted by a first-principles calculation

Abstract

Hybrid improper ferroelectricity (HIF) is recognized as a promising way to design room-temperature multiferroic materials with strong magnetoelectric coupling. However, predicting new HIF materials with high ferroelectric polarization remains to be a great challenge. Here, the new compound $\mathrm{B}{\mathrm{a}}_{3}\mathrm{C}{\mathrm{e}}_{2}{\mathrm{O}}_{7}$ with Ruddlesden-Popper (R-P) structure, which crystallizes in polar $A{2}_{1}am$ phase has been proposed and its HIF has been demonstrated using the first-principles calculation. The ferroelectric polarization stems from the condensation of in-phase rotation and out-of-phase tilt modes. The correlations between orbital interactions, structural distortions and ferroelectric properties have also been clarified. Moreover, the presence of negative hydrostatic pressure will generate large octahedral distortions and noncancelled anti-ferrodistortive displacements at $A$-site, resulting in the significant enhancement of polarization. The pressure engineering renders a guideline for tuning HIF and designing ferroelectrics in R-P compounds.