Abstract
The diffraction theory evolved by Matsubara, Kanzaki and Krivoglaz for solid solutions has been extended so that it may be applied to thermal diffuse scattering (TDS) from an ordered phase. The TDS intensity is calculated by using the extended theory on a β-brass (Cu–47.5 at%Zn), which shows strong diffuse streaks along the 110 rel. direction in X-ray diffraction patterns taken at room temperature. As a result, the diffuse streaks are shown to occur primarily by the soft TA2 phonon mode in the B2 type ordered lattice of the β-brass. Intensity measurements of diffuse streaks have also been made by using a single crystal of the β-brass. On subtraction of the calculated TDS intensity from the measured one, solute-lattice coupling parameters are obtained to the third neighbor of atoms. From the solute-lattice coupling parameters, three elastic constants, c11, c12 and c44, of the β-brass are estimated, and they are in good agreement with those obtained by an ultrasonic method.
