Third Law Entropy of Barium Molybdate

The isobaric heat capacities, C degrees(p,m), for BaMoO4 at 2-300 K were measured by the relaxation method. The third law entropy, S degrees(m),was determined via the Debye-Einstein function into which the Debye temperature, Theta(D), as physico-chemical constant and a thermal expansion term were incorporated. Theta(D) was determined from C degrees p,m at very low temperatures. The obtained thermodynamic properties were: S degrees(m) (BaMoO4(cr), 298.15 K)/JK(-1)mol(-1) = 152.69 +/- 1.53; Theta(D)(BaMoO4(cr))/K = 295 +/- 3. The phase stability of BaMoO4 was discussed on the basis of its standard Gibbs energy of formation, Delta(f)G degrees(m). It was derived by combining S degrees R-m, determined in this study with the reference data of the standard enthalpy of formation, Delta(f) H degrees(m).The thermodynamic properties obtained in the present study can be used for evaluating the hierarchy for formation of the yellow phase related-substances in nuclear waste glasses.