Cascos Vanessa A, Roberts-Watts Jennifer, Skingle Chloe, Levin Igor, Zhang Weiguo, Halasyamani P Shiv, Stennett Martin C, Hyatt Neil C, Bousquet Eric, McCabe Emma E
School of Physical Sciences, University of Kent, Canterbury Kent CT2 7NH, U. K.
Materials Measurement Science Division, NIST, Gaithersburg, Maryland 20899, United States.
Chem Mater. 2020 Oct 13;32(19):8700-8712. doi: 10.1021/acs.chemmater.0c03326. Epub 2020 Sep 22.
The Dion-Jacobson (DJ) family of perovskite-related materials have recently attracted interest due to their polar structures and properties, resulting from hybrid-improper mechanisms for ferroelectricity in = 2 systems and from proper mechanisms in = 3 CsBiTiNbO. We report here a combined experimental and computational study on analogous = 3 Cs TiNbO ( = La, Nd) materials. Density functional theory calculations reveal the shallow energy landscape in these systems and give an understanding of the competing structural models suggested by neutron and electron diffraction studies. The structural disorder resulting from the shallow energy landscape breaks inversion symmetry at a local level, consistent with the observed second-harmonic generation. This study reveals the potential to tune between proper and hybrid-improper mechanisms by composition in the DJ family. The disorder and shallow energy landscape have implications for designing functional materials with properties reliant on competing low-energy phases such as relaxors and antiferroelectrics.
由于其极性结构和性质，与钙钛矿相关的狄翁 - 雅各布森（DJ）族材料近来引起了人们的关注，这是由二维系统中铁电的混合非本征机制以及三维CsBiTiNbO中的本征机制导致的。我们在此报告对类似的三维CsTiNbO（R = La，Nd）材料进行的实验与计算相结合的研究。密度泛函理论计算揭示了这些系统中浅的能量态势，并对中子和电子衍射研究提出的相互竞争的结构模型给出了理解。由浅能量态势导致的结构无序在局部层面打破了反演对称性，这与观察到的二次谐波产生一致。这项研究揭示了通过DJ族中的成分在本征和混合非本征机制之间进行调节的潜力。这种无序和浅能量态势对于设计具有依赖于诸如弛豫铁电体和反铁电体等相互竞争的低能相性质的功能材料具有启示意义。
