Lattice parameters and thermal expansion of solid orthodeuterium

X-ray studies have been carried out of the lattice parameters, molar volume, and thermal expansion coefficient of solid orthodeuterium in the range from 2 K to the melting temperature of the crystal. It was found that near the melting temperature the thermal expansion of orthodeuterium, as of parahydrogen, is essentially anisotropic. The vacancy concentration at the triple point is estimated. Some thermodynamic characteristics of orthodeuterium have been calculated and the temperature dependence of the heat capacity at constant volume, of the isothermal compressibility and of the Griineisen parameter are analyzed.