Dispersion Relations and Elastic-Wave Velocities of External Lattice Vibration Modes Propagating Along c-Axes in Scheelites

The dispersion relations in CaWO4, CaMoO4, SrMoO4, BaWo4, BaMoO4, NH4ReO4 and ND4ReO4, are determined from the two possible sets of force constants given in J. Phys. Soc. Japan 36 (1974) 511 and 916; the words, case I and II, were used to distinguish the two sets of the constants. The sets corresponding to the case II are not suitable to the two perrhenates, as they give imaginary frequencies. The elastic-wave velocities are determined as the gradients of the dispersion relations of the acoustic branches at k=0. The comparison of the theoretical velocities with the observed values suggests that the set corresponding to the case I is reasonable for CaMoO4. © 1974, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.