Crystal structures of highly hole-doped layered perovskite nickelate PrSrNiO studied by neutron diffraction

Kajimoto, Ryoichi  ; Nakajima, Kenji  ; Fujita, Masaki*; Ishikado, Motoyuki*; Torii, Shuki*; Ishikawa, Yoshihisa*; Miao, P.*; Kamiyama, Takashi*

A high-resolution time-of-flight powder neutron diffraction study of the layered nickel oxide PrSrNiO with and was performed to characterize the crystal structures of these highly hole-doped nickelates. For the sample with , the Ni-O bond lengths decrease uniformly with decreasing temperature, and the atomic displacement parameters are similar to those for . In contrast, for the sample with , the out-of-plane Ni-O bond length shows a sharp thermal contraction in the high-temperature region, which is suggestive of changes in the orbital occupation accompanied by the development of checkerboard-type charge correlations. Furthermore, the sample is characterized by a large atomic displacement parameter for the apical O atoms along the out-of-plane direction, which is interpreted as the existence of two types of Ni sites with different orbital occupancies. The distinct difference between the sample and the lower-concentration compounds should be related to the development of checkerboard-type charge ordering in the metallic matrix and possible orbital ordering at the Ni sites at in the hole-doped layered nickel oxides.