Abstract
Temperature variation of the crystal structure has been investigated for ${\mathrm{TbBaCo}}_{2}{\mathrm{O}}_{5+\ensuremath{\delta}} (\ensuremath{\delta}=0.5),$ which shows a metal-insulator (MI) transition at ${T}_{\mathrm{MI}}\ensuremath{\approx}340 \mathrm{K}.$ The compound has an oxygen-deficient perovskite structure, with alternating ${\mathrm{CoO}}_{6}$ octahedral and ${\mathrm{CoO}}_{5}$ pyramidal chains along the crystallographic $b$ axis. We have found that both the pyramids and octahedra are significantly distorted in the insulating phase below ${T}_{\mathrm{MI}},$ suggesting a ${d}_{{3x}^{2}\ensuremath{-}{r}^{2}}{/d}_{{3y}^{2}\ensuremath{-}{r}^{2}}\ensuremath{-}\mathrm{type}$ orbital ordering.
Published Version
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