SOLID PARADEUTERIUM - LATTICE-PARAMETERS AND THERMAL-EXPANSION

We have obtained for the first time systematic data on the lattice parameters, the molar volume, the density, the x-ray thermal expansion of the high-temperature hcp phase of paradeuterium (x(f=1) = 0.86) in the temperature range 4.5 to 18.5 K. By comparison with the previous results for orthodeuterium (x(f=1) = 0.025), we have determined how the quadrupolar subsystem influences the structural (lattice parameters and volume) and thermodynamic (thermal expansion, Gruneisen constant) properties of deuterium. The quadrupolar pressure effect is shown to be the highest at low temperatures, where the decisive contribution to the properties of crystals is given by the rotational subsystem.