Oliveira G N P, Teixeira R C, Moreira R P, Correia J G, Araújo J P, Lopes A M L
IFIMUP-Instituto de Física de Materiais Avançados, Nanotecnologia e Fotónica, Departamento de Física e Astronomia da Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 687, 4169-007, Porto, Portugal.
C2TN, Centro de Ciências e Tecnologias Nucleares, Departamento de Engenharia e Ciências Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066, Bobadela, LRS, Portugal.
Sci Rep. 2020 Mar 13;10(1):4686. doi: 10.1038/s41598-020-61384-6.
Rare-earth orthochromites with distorted perovskite structure (e.g. RCrO, R = Sm, Gd) have been under strong debate with respect to the origin of their ferroelectric order. Of particular interest is the question of whether such orthochromites are, in fact, magnetically driven improper ferroelectrics, as many rare-earth manganites or orthoferrites. Here we show, by studying at the atomic scale the rare-earth SmCrO system that a distortion of the Sm local environment emerges within the paramagnetic phase, near room temperature. Our Electric Field Gradient measurements combined with first-principles calculations show that the emergent phase cannot be simply ascribed to the Pna2 structure as reported for GdCrO or SmCrO. Instead a local inhomogeneous state, where regular non-polar and polar distorted environments coexist, develops at low temperatures.
具有畸变钙钛矿结构的稀土正铬酸盐（例如RCrO，R = Sm，Gd），其铁电有序起源一直存在激烈争论。特别令人感兴趣的问题是，这类正铬酸盐是否实际上像许多稀土锰酸盐或正铁酸盐一样，是磁驱动的非本征铁电体。在此，我们通过在原子尺度上研究稀土SmCrO系统表明，在接近室温的顺磁相中，Sm局部环境会出现畸变。我们的电场梯度测量结合第一性原理计算表明，出现的相不能简单地归因于如GdCrO或SmCrO所报道的Pna2结构。相反，在低温下会形成一种局部非均匀状态，其中规则的非极性和极性畸变环境共存。
