Abstract
The formalism of higher order elasticity theory, which is used to describe the finite deformation of crystals, is at first presented. The importance of the higher order elastic constants, which are defined as the higher-order finite-strain derivatives of crystal energy, is emphasized. Experimental methods for determining the higher order elastic constants of crystals and also theoretical aspects of calculating the higher order elastic constants of various kinds of materials are explained. Two examples of application of the higher order elasticity theory for treating anharmonic properties of crystals ae shown, namely, the thermal expansion of crystals and the scattering of phonons by static strain fields in crystals.
