Observation of two charge ordering transitions in the valence-fluctuating EuPtP by resonant X-ray diffraction

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

Two first-order phase transitions of the valence-fluctuating compound EuPtP at =246 K and =200 K were examined by means of resonant X-ray diffraction at the Eu absorption edge. Although previous Mssbauer spectroscopy and preliminary X-ray diffraction experiments have suggested charge ordered states, characteristic energy spectra of the 111 and 11 reflections observed in the present experiment unambiguously indicated that twofold and threefold superstructures of Eu valence exist below and between and , respectively. We also propose a mechanism to explain the charge ordering in EuPtP based on a charge-lattice coupling that alters a Coulomb repulsion.