Lattice parameters and thermal expansion of solid paradeuterium

Systematic data are obtained for the first time on the lattice parameters, molar volume, density, and the x-ray thermal expansion coefficients of the high-temperature hcp phase of p-D2 (xJ = 1 = 0.86) in the temperature interval 4.5–18.5 K. Quantitative characteristics of the effect of the quadrupole subsystem on structural (parameters and lattice volume) and thermodynamic (thermal expansion and Gruneisen’s constant) properties of deuterium are obtained from a comparison with the results of previous investigations of orthodeuterium (xJ = 1 = 0.025). It is shown that the effect is the strongest at low temperatures when the contribution from the rotational subsystem dominates.