Elastic constants of ammonium fluoroberyllate by thermal diffuse scattering of X-rays
AbstractAll 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.