ELASTIC-CONSTANTS AND ACOUSTIC SYMMETRY OF LIYF4

The elastic behaviour of the scheelite-structure, laser host crystal LiHF4, determined from ultrasonic measurements of the seven adiabatic elastic stiffness moduli Cijkl between 4.2 and 293K, is expressed in terms of the acoustic symmetry which occurs in such TII Laue crystals. To establish the sense of the Z axis with respect to the interatomic arrangement and the setting angle ( phi s=+29 degrees ) of the fluorine ion tetrahedron, the positions of the fluorine atoms have been determined by X-ray methods. The signs of C16 and S16 and the sense of rotation in the XY plane about the Z axis of the acoustic symmetry axes are established. The kappa and gamma axes of the acoustic symmetry are used together with the +Z axis as a basis for a set of transformed elastic stiffness constants C'ijkl. The elastic behaviour is directly compared and contrasted with the oxide scheelites CaWO4, CaMoO4, SrMoO4 and PbMoO4.