(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.
|Number of pages||5|
|Journal||Physical review B|
|Early online date||1 Jul 2005|
|Publication status||Published - 2005|