The magnetic transition, heat capacity, and thermodynamic properties of uranium dioxide from 5 to 350 K

The heat capacity of high purity uranium dioxide has been re-examined over the low-temperature range especially in the vicinity of the λ-type anomaly reported to occur at 28·7 K as a consequence of magnetic ordering. The present study indicates a very sharp transition at 30·44 K with a maximum C_p of 391 cal mol^-1 K^-1. The heat capacity at constant pressure C_p, the entropy S°, the enthalpy (H° - H°₀), and Gibbs energy function (G° - H°)/T are tabulated and at 298.15 K have the following values: 15.20 cal mol^-1 K^-1, 18.41 cal mol^-1 K^-1, 2696 cal mol^-1 K^-1, and -9.37 cal mol^-1 K^-1. The heat capacity results are compared with those derived from the neutron scattering work and also with the theory of Allen.