Abstract
The heat capacities of uranium diarsenide (UAs 2) and uranium diantimonide (USb 2), with tetragonal structures of the anti-Cu 2Sb-type, have been measured by adiabatic-shield calorimetry from 5 to about 750 K. Lambda-type transitions with maxima at 272.2 and 202.5 K for UAs 2 and USb 2, respectively, are related to maxima in the magnetic susceptibilities at 277 and 203 K, occasioned by transitions from antiferro- to paramagnetism in the compounds. Values of the heat capacities ( C p ), entropies [ S°( T) − S°(0)], and Gibbs energy functions −{[ G°( T) − H°( o)]/ T} at 298.15 K in cal K −1 mole −1 are 19.12, 29.41 and 15.05 for UAs 2 and 19.16, 33.81 and 18.39 for USb 2. Tentative resolutions of the cooperative magnetic heat capacities of UAs 2 and USb 2 lead to the magnetic entropies ΔS(mag) = 0.99 and 1.70 cal K −1 mole −1, respectively. The values for both are significantly lower than the spin-only magnetic entropy value R ln 3 = 2.18 cal K −1 mole −1.
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