The coexistence of multiferroic orders has attracted increasing attention for its potential applications in multiple-state memory, switches, and computing, but it is still challenging to design single-phase crystalline materials hosting multiferroic orders at above room temperature. By utilizing versatile ABX₃-type perovskites as a structural model, we judiciously introduced a polar organic cation with easily changeable conformations into a tetrafluoroborate-based perovskite system, and successfully obtained an unprecedented molecular perovskite, (homopiperazine-1,4-diium)[K(BF₄)₃], hosting both ferroelectricity and ferroelasticity at above room temperature. By using the combined techniques of variable-temperature single-crystal X-ray structural analyses, differential scanning calorimetry, and dielectric, second harmonic generation, and piezoresponse force microscopy measurements, we demonstrated the domain structures for ferroelectric and ferroelastic orders, and furthermore disclosed how the delicate interplay between stepwise changed dynamics of organic cations and cooperative deformation of the inorganic framework induces ferroelectric and ferroelastic phase transitions at 311 K and 455 K, respectively. This instance, together with the underlying mechanism of ferroic transitions, provides important clues for designing advanced multiferroic materials based on organic–inorganic hybrid crystals.

中文翻译：

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室温铁电和铁弹性有序共存于新型四氟硼酸盐基钙钛矿中


多铁性有序的共存因其在多状态存储器、开关和计算中的潜在应用而引起了越来越多的关注，但设计在室温以上具有多铁性有序的单相晶体材料仍然具有挑战性。通过利用通用的ABX ₃型钙钛矿作为结构模型，我们明智地将一种具有易于改变构象的极性有机阳离子引入到基于四氟硼酸盐的钙钛矿体系中，并成功获得了前所未有的分子钙钛矿（homopiperazine-1,4-diium）[ K(BF ₄ ) ₃ ]，在室温以上同时具有铁电性和铁弹性。通过使用变温单晶X射线结构分析、差示扫描量热法、介电、二次谐波产生和压响应力显微镜测量的组合技术，我们展示了铁电和铁弹性级的域结构，并进一步揭示了如何有机阳离子的逐步变化的动力学与无机框架的协同变形之间的微妙相互作用分别在 311 K 和 455 K 引起铁电和铁弹性相变。这一实例以及铁性转变的基本机制，为设计基于有机-无机杂化晶体的先进多铁性材料提供了重要线索。