HIGHER-ORDER ELASTIC-CONSTANTS AND GENERALIZED GRUNEISEN PARAMETERS OF ELASTIC-WAVES AND LOW-TEMPERATURE THERMAL-EXPANSION OF DYSPROSIUM

The expressions for the 19 fourth order elastic constants, 10 third or der elastic constants and six second order elastic constants are deriv ed using the method of homogenous deformation with interactions extend ing up to second neighbours using the sublattice displacements to the second degree in strains, These expressions are used to obtain the hig her order elastic constants and their pressure derivatives in dysprosi um. Dysprosium belongs to the hexagonal class of crystals. The higher order elastic constants are used to find out the generalised Gruneisen parameters of the elastic waves propagating in different directions i n dysprosium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared wi th the available reported values. (C) 1997 Elsevier Science Ltd. All r ights reserved.