Elastic constants of ammonium fluoroberyllate by thermal diffuse scattering of X-rays
Abstract
All the nine elastic constants of orthorhombic ammonium fluoroberyllate (NH4)2.BeF4 have been determined at room temperature (305 K) from the measurement of the intensities of thermal diffuse scattering of X-rays using a single-crystal diffractometer. Monochromatic Mo K radiation obtained by reflection from a curved quartz crystal was used. The intensity of diffusely scattered X-rays has been corrected for divergence, polarization, skew correction, absorption, second-order thermal diffuse scattering and general scattering. Isodiffusion contours have been drawn around the 400 node. The values of elastic constants in units of 1010 Nm-2 are C11 = 3.82 (30), C22 = 3.56 (28), C33 = 2.45 (19), C44 = 0.96 (05), C55 = 1.01 (05), C66 = 0.79 (04), C12 = 1.78 (18), C13 = 1.52 (15), C23 = 1.41 (14). An estimate of the Debye temperature has been made by calculating the mean sound velocity in the crystal from these elastic-constant values.