Zhang Yajun, Wang Jie, Ghosez Philippe
Theoretical Materials Physics, Q-MAT, CESAM, Université de Liège, B-4000 Liège, Belgium.
Department of Engineering Mechanics and Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China.
Phys Rev Lett. 2020 Oct 9;125(15):157601. doi: 10.1103/PhysRevLett.125.157601.
The competition between polar distortions and BO_{6} octahedra rotations is well known to be critical in explaining the ground state of various ABO_{3} perovskites. Here, we show from first-principles calculations that a similar competition between interlayer rumpling and rotations is playing a key role in layered Ruddlesden-Popper (RP) perovskites. This competition explains the suppression of oxygen octahedra rotations and hybrid improper ferroelectricity in A_{3}B_{2}O_{7} compounds with rare-earth ions in the rocksalt layer and also appears relevant to other phenomena like negative thermal expansion and the dimensionality determined band gap in RP systems. Moreover, we highlight that RP perovskites offer more flexibility than ABO_{3} perovskites in controlling such a competition and four distinct strategies are proposed to tune it. These strategies are shown to be promising for designing new multiferroics. They are generic and might also be exploited for tuning negative thermal expansion and band gap.
众所周知，极性畸变与BO₆八面体旋转之间的竞争对于解释各种ABO₃钙钛矿的基态至关重要。在此，我们通过第一性原理计算表明，层间褶皱与旋转之间的类似竞争在层状Ruddlesden-Popper（RP）钙钛矿中起着关键作用。这种竞争解释了在具有岩盐层中稀土离子的A₃B₂O₇化合物中氧八面体旋转和混合非本征铁电性的抑制，并且似乎与其他现象相关，如负热膨胀以及RP体系中维度决定的带隙。此外，我们强调RP钙钛矿在控制这种竞争方面比ABO₃钙钛矿具有更大的灵活性，并提出了四种不同的策略来调节它。这些策略对于设计新型多铁性材料很有前景。它们具有通用性，也可能用于调节负热膨胀和带隙。
