Uranium monosulfide. The ferromagnetic transition. The heat capacity and thermodynamic properties from 1.5° to 350°K

Abstract

The heat capacity of uranium monosulfide was measured from 1.5° to 22°K by an isothermal (isoperibol) method and from 6° to 350°K by an adiabatic technique. The ferromagnetic transition at 180.1°K has a characteristic lambda shape and associated magnetic ordering entropy and enthalpy increments of 1.62±0.2 cal°K-1 mole-1 and 231±20 cal mole-1, respectively, over the temperature range 0° to 230°K. The correlation of the thermal data with magnetic studies is discussed. The heat capacity below 9°K is represented by Cp=5.588×10-3T+2.627×10 -4T3/2+6.752×10-5T3 cal °K-1 mole-1, in which the successive terms represent conduction electronic, magnetic, and lattice contributions. Values of the entropy [S°], enthalpy function [(H°-H°0)/T], and Gibbs-energy function [(G°-H°0)/T] are 18.64±0.05, 8.94±0.02, and -9.70±0.02 cal °K-1 mole -1, respectively, at 298.15°K. The Gibbs energy of formation at 298.15°K is -72.9±3.5 kcal mole-1.