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

Expressions for the higher order elastic constants are derived using t he sublattice displacements to the second degree in strains. These exp ressions are used to obtain the higher order elastic constants and the ir pressure derivatives in gadolinium. The higher order elastic consta nts are used to find out the generalized Gruneisen parameters of the e lastic waves propagating in different directions in gadolinium. The Br ugger gammas are evaluated and the low temperature limt of the Gruneis en gamma is obtained. The results are compared with the available repo rted values.