Specific heat of solid nitrogen-argon mixtures: 50 to 100 mol%N2

Abstract

We have measured the specific heat, $C_p$, of solid ${\mathrm{N}}_2$-argon alloys of 49.75, 62.83, 70.43, 79.85, and 100 mol% ${\mathrm{N}}_2$ concentration between 4.5 and 40 K. The measurements were made to investigate the possible formation of a rotational glass phase similar to that of solid ${\mathrm{H}}_2$. The three lower-concentration samples showed no evidence of a sharp transition to a glass phase nor any thermal remanence indicative of a glass, although the rotational contribution to the specific heat was qualitatively similar to that of the solid ${\mathrm{H}}_2$ glass. The 49.75-mol% sample did not exhibit the martensitic hcp-to-fcc crystalline transition expected at 23 K, indicating that cold working is important to forcing this transition. The $\alpha -\beta$ phase transition in pure ${\mathrm{N}}_2$ was very sharp upon cooling to the transition point, without any pretransitional effects, whereas the $\alpha -\beta$ transition in the 79.85-mol% sample had a $\lambda$-like appearance.