An X-ray investigation of atomic vibrations in magnesium between 86 and 293 K.

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Abstract
Measurements are made of the intensities of X-ray reflections from magnesium powder at 86° and 293° K. Absolute values of the ratio I86/I293 are obtained by making comparative measurements on a composite specimen of magnesium and aluminium powders. The results are discussed in relation to theoretical work by Zener and others on the effect of lattice vibrations in hexagonal metals on the intensities of X-ray reflections. It is shown that in magnesium the lattice vibrations are almost isotropic but that the mean atomic displacements in the basal plane are about 3 per cent greater than those parallel to the c axis. Values are calculated for the mean atomic displacements in these directions at 86° and 293° K., and the results are also expressed in terms of characteristic temperatures Θ0 (parallel to the c axis), equal to 339°, and Θ90, equal to 327°. A consideration of these results, in conjunction with similar results for other hexagonal metals, points to a correlation between the departure of the axial ratio from the ideal value 1.633 and the asymmetry of the lattice vibrations.