Structural Evolution of Corundum at High Temperatures

概要

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The evolution of the corundum ($\alpha$-Al2O3) structure was investigated at 297, 573, 873, and 1173 K using the single-crystal X-ray diffraction method and molecular dynamics simulation. The results were smoothly extrapolated to the previously reported high-temperature data of the compound at 2170 K [Ishizawa et al.: Acta Crystallogr., Sect. B 36 (1980) 228], revealing a significant shift of the fractional coordinate $z$ of the Al atom as a function of temperature. The Al atom shift indicates that the Al$\cdots$Al intermetallic repulsion force across a pair of face-sharing octahedra becomes conspicuous over other interatomic forces at high temperatures. The increasing Al$\cdots$Al repulsion is relieved by both the preferential expansion of a unit cell along the $c$-axis and the change in the $z$ coordinate of the Al atom. The results of molecular dynamics simulation experiments qualitatively agreed with the X-ray diffraction data. The thermal expansion of the crystal was well described by the quadratic functions, $a = 4.75385\ (1.0 + 5.05841\times 10^{-6}\ T + 1.69084\times 10^{-9}\ T^{2})$ Å, and $c = 12.9782\ (1.0 + 4.61344\times 10^{-6}\ T + 2.63802\times 10^{-9}\ T^{2})$ Å.
2008-01-25