Crystal structure refinement of AlN and GaN

We have refined the structure parameters of AlN and GaN using X-ray intensities from single crystals collected with an automatic single crystal diffractometer. The lattice constants and the u values are a = 3.110 Å, c = 4.980Å, u = 0.3821 for AlN and a = 3.190Å, c = 5.189 Å, u = 0.377 for GaN. The final R-values for anisotropic temperature factors are equal to 0.015 for AlN and 0.026 for GaN. The effective atomic charges in these compounds are estimated.