Resonant X-ray diffraction study on the charge ordering transitions in the mixed valent compound EuPtP

混合原子価化合物EuPtPの電荷秩序の共鳴X線回折による研究

稲見 俊哉; 道村 真司; 光田 暁弘*; 和田 裕文*

Inami, Toshiya; Michimura, Shinji; Mitsuda, Akihiro*; Wada, Hirofumi*

We report on direct observations of the charge-ordered states in the ternary rare-earth compound EuPtP by means of resonant X-ray diffraction (RXD) at the Eu absorption edge. Based on the inhomogeneous valence states obtained by Mssbauer measurements, it is proposed that two first-order transitions at =246 K and =200 K accompany charge ordering of the Eu valency. We first searched superlattice and forbidden reflections and found (1 1 1) and (1 1 11/3) reflections at the low-temperature phase () and the intermediate phase (), respectively. These reflections exhibited characteristic photon-energy dependence, and the measured energy spectra were well reproduced by assuming spatial order of the Eu valency. As a result, we conclude that three-fold and two-fold superstructures of Eu valency exist in EuPtP between and and below , respectively. We also considered a lattice effect as a possible mechanism of charge ordering in metallic EuPtP.