Orbital ordering and valence states in (La1+xCa1-x)CoRuO6 double perovskites

Jan-willem Bos, J. Attfield, Ting-shan Chan, Ru-shi Liu, Ling-yun Jang

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(La1+xCa1−x)CoRuO6 double perovskites have been studied by neutron diffraction and x-ray absorption spectroscopy. The thermal evolution of the (LaCa)CoRuO6 structure has been investigated between 4 and 1073 K using neutron powder diffraction. The cell b axis shows a crossover from negative to positive thermal expansion at T≈425 K, which is accompanied by a discontinuity in the c axis. This is shown to result from a partial orbital ordering of the Co2+ t2g holes. Ru valence states of doped (La1+xCa1−x)CoRuO6 (−0.25≤x≤0.25) materials have been investigated using XANES spectroscopy. Electron-doping (x>0) leads to reduction of Ru5+→Ru4+ while hole-doped x≤0 compositions have a constant Ru5+ state. These observations support a proposed asymmetric doping model.

Original languageEnglish
Article number014101
Number of pages5
JournalPhysical review B
Issue number1
Early online date1 Jul 2005
Publication statusPublished - 2005


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