Neutron Diffraction Determination of Mean-square Atomic Displacements in InAs and GaSb

Abstract

Integrated intensities for Bragg reflection of neutrons from single crystals of the III-V compounds InAs and GaSb have been measured at room temperature. The data were collected at two wavelengths, 0'947 and 1�241 A, in order' to establish the adequacy of a correction for moderate to severe anisotropic extinction. Data were also obtained for InAs at four temperatures from 408 to 933 K. Corrections for thermal diffuse scattering were applied. The results were analysed in the one-particle potential perturbation approximation with terms to fourth order in the atomic displacements u == (ut, U2, U3)' At 296 K, the mean-square components <u;) determined were: In, 0'0116(2) A2; As, 0'0102(1) A2; and Ga, 0,0120(3) A2; Sb, 0,0107(3) A2. The third-order coefficients for InAs are comparable with those for Si and Ge, while those for GaSb are comparable with those for zinc cha1cogenides. Below 400 K, the mean-square displacements in InAs decrease faster than predicted by the present perturbation approach.