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 Ba3Ce2O7 with Ruddlesden-Popper (R-P) structure, which crystallizes in polar A21am 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.

中文翻译：

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用第一性原理预测Ba3Ce2O7的混合不当铁电和压力引起的极化增强

混合不当铁电（HIF）被认为是设计具有强磁电耦合的室温多铁材料的一种有前途的方法。然而，预测具有高铁电极化的新型HIF材料仍然是一个巨大的挑战。在这里，提出了一种新的具有Ruddlesden-Popper（RP）结构的化合物Ba3Ce2O7，该化合物在极性A21am相中结晶，并且已经通过第一性原理计算证明了其HIF。铁电极化源于同相旋转和异相倾斜模式的凝结。轨道相互作用，结构变形和铁电特性之间的关系也已经阐明。此外，负静水压力的存在会在A位置产生大的八面体形变和不可取消的反铁变形位移，从而导致极化显着增强。压力工程为调整HIF和设计RP化合物中的铁电体提供了指南。