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