Studies of the dielectric constant in solid H2,4He, and Ne

Measurements of the static dielectric constant ε and of the resulting polarizability αCM defined by the Clausius-Mosotti relation are reported for several molecular solids under conditions of quasiconstant density. The range of measurements was between 0.4 and about 15 K, and pressures up to about 1 kbar were used. In solid H2, the changes of α as a function of ortho concentration are reported at 4.2 and 12 K, from which it is concluded that [α(ortho)−α(para)]/α≃0.005, which is approximately 2 1/2 times larger than in the liquid phase. Furthermore the temperature change of αCM is studied for various densities at comparable ortho concentrationsX. Particular attention is paid to the orientational order-disorder transition in solid H2 withX≃0.65, where αCM shows an abrupt change that appears to be a function ofX, density, and thermal history. In general αCM is lower in the ordered (cubic) phase than in the disordered (hexagonal) phase. The temperature change of αCM in almost pure para-H2, measured between 4 and 0.4 K, is presented and is compared with other recently reported experiments. It is concluded that the mechanism that produces the change of αCM withT and at the order-disorder phase transition is not understood. In solid Ne, measurements of αCM are reported for one sample assumed to be at zero pressure and one where the density is quasiconstant. There is a strong temperature dependence in αCM for the former above 5 K (in agreement with previous findings), while for the latter αCM appears to be constant within the uncertainties introduced by strain-induced hysteresis effects. The sample of solid4He, investigated between its melting point at 4.3 and 0.8 K at constant density, shows a very weak temperature dependence of αCM, which is also consistent with previously reported measurements.