Pressure transitions in solid H 2 below 0.5 K

Abstract

We report measurements of orthohydrogen conversion induced pressure changes in samples of solid H 2 held at constant temperatures below 0.5 K. Sudden pressure changes were noted at orthohydrogen concentrations, X( J = 1) ≈ 0.53, as the samples converted from the ordered f.c.c. structure to the quadrupolar glass region. These results are compared with NMR and X-ray evidence concerning the f.c.c. phase boundary at low temperatures.