Charge ordering in Eu3S4 determined by the valence-difference contrast of synchrotron X-ray diffraction

摘要

Synchrotron X-ray diffraction study for single crystals of E u(3)S(4) has revealed that a Th3P4-type 143d structure transforms to a charge-ordered I42d one at T-c = 188.5 K. The crystal structures of Eu3S4 at T = 300, 180 and 160 K were determined in the least-squares refinements with the Mo Kalpha intensity data. The valence-difference contrast method was applied at the Lit absorption edge of Eu, utilizing a large difference in anomalous scattering factors between Eu2+ and Eu3+. The cation distribution of Eu2+ and Eu3+ was determined by crystal-structure analyses based on the intensity data collected at two wavelengths of lambda = 1.6312 and 1.6298Angstrom.The least-squares structural refinements suggest that the most plausible atomic arrangement is [Eu3+](4a) [Eu2+ Eu3+]S-8d(4). The charge-ordering scheme is that a half of Eu3+ ions occupy the whole 4a sites in the I42d crystal structure, while the remaining half of Eu3+ ions mix with Eu2+ in the 8d sites. The scheme is also supported by the energy dependence of Bragg intensities for 400 and 004 reflections. (C) 2004 Elsevier B.V. All rights reserved.