The Low-Temperature Anisotropic Thermal Expansion of Calcium Tungstate

Interferometric measurements of the linear thermal expansion coefficients are reported for thec andacrystallographic axis directions of calcium tungstate in the temperature range 30–270°K. The results are believed to be accurate to within 2% at 270°K, falling to 25% at 30°K. The reduced mean Grüneisen parameter (χ _s γ _mean ) = βV/C _t, calculated from the volume expansion coefficient β and earlier heat-capacity measurements, falls with diminishing temperature. Detailed identification of contributions to the thermodynamic properties arising from translational, rotational, and internal modes of vibration is prevented by spectral overlap. The quasiharmonic approximation has been applied to calculate provisional reduced moments of a representative vibrational frequency spectrum, which are in qualitative accord with earlier findings based upon observations of infrared reflection and first-order Raman spectra.

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