High temperature elasticity of rutile-structure MgF2

The elastic moduli of single-crystal MgF₂ have been determined by the ultrasonic pulse superposition technique as a function of temperature from T=298?650° K. These new data are consistent with those obtained by other ultrasonic pulse techniques at and below room temperature and agree favourably with polycrystalline data above room temperature. The elastic moduli (c) are represented by quadratic functions in T over the experimental temperature range with the curvature in the same sense for all the moduli. For the rutile-structure fluorides and oxides, evaluation of the temperature derivatives of the elastic moduli at constant volume indicates that the dominant temperature effect is extrinsic for (?K _S /?T) _P and intrinsic for (?μ/?T) _P , where K _S and μ are the isotropic bulk and shear moduli, respectively. There appears to be no simple relationship between (?c/?T) _P and crystallographic parameters for the rutile structure, and |(?c/?T) _P | for the fluorides is in general very much lower than the corresponding |(?c/?T) _P | for the oxides. For the pair of compounds MgF₂-TiO₂, there is no evident analogue relationship for high-temperature elastic properties.