Rietveld-refinement study of aluminium and gallium nitrides

Powder diffraction data for fine AlN and GaN powders were collected at a Bragg-Brentano diffractometer equipped with a Johansson monochromator and a semiconductor strip detector. Rietveld-refinements were performed in order to determine the structural parameters of these wurtzite-type (space group, P63mc) materials. The following crystallographic data were obtained: a 3.11197(2) A, c = 4.98089(4) A, c/a =1.60056(2), u = 0.3869(5) for aluminium nitride and a = 3.28940(1) A, c = 5.18614(2) A, c/a = 1.62606(1), u 0.3789(5) for gallium nitride. These structural data are discussed in the light of earlier experimental and theoretical results