The effect of n-H2 impurity on the heat capacity of solid Ne

Abstract

The alloy Ne-5.1% n-H2 is investigated calorimetrically under equilibrium vapor pressure in an interval of 0.9–25K. The magnitude and temperature dependence of the heat capacity Csol(T) of the alloy at T=11–20K are found to be strongly dependent on the conditions of sample preparation. The temperature dependence of Csol(T) for the sample prepared in a calorimeter by direct condensation of a gas mixture at T≈15K exhibits a smeared maximum near the triple-point temperature of hydrogen and a phase transition at T=17.1K. The detected features of Csol(T) indicate that preparation of solid Ne–n-H2 from the gas phase leads to the formation of a long-lived nonequilibrium phase of Ne with high H2 concentrations and a small portion of H2 inclusions with low Ne concentrations. The phase transition is caused by decomposition of this phase. The phase does not recover on cooling of the sample after the phase transition. It is found that the rate of ortho-para conversion of the H2 molecules in the Ne–n-H2 solid solutions is higher than in solid H2.