Specific heat, pressure, and the Gr�neisen relation in solid hydrogen

Abstract

We report systematic measurements ofC v and (∂P/∂T) v in solid hydrogen below 1 K and for orthohydrogen molar concentrations 0.58≥X ortho≥0.20. This is the temperature and concentration range associated with a proposed quadrupolar glass phase. The results show no overtly glassy properties such as remanence or hysteresis upon warming and cooling, and there is no evidence of anomalous thermal relaxations. We have calculated the quadrupolar Gruneisen constant from our data and find that γ is only a slowly varying function of temperature and orthohydrogen concentration. TheC v results are compared with theoretical models and the behavior of a corresponding classical solid, N2-argon. There are several similarities between the N2-argon and H2 behaviors, but the semiempirical single-particle model does not correspond well with the experimental results.