Third Law Entropy of Silver Molybdate

Abstract

The isobaric heat capacities, C^°_p,m, for Ag₂MoO₄ at 2-300 K were measured by the relaxation method. Ag₂MoO₄ is harmful phase formed in nuclear fuel waste glasses. The third law entropy, S^°_m, determined via the Debye-Einstein function was: S^°_m(Ag₂MoO₄(cr), 298.15 K)/J K^-1 mol^-1 = 219.87 ± 2.20. The phase stability of Ag₂MoO₄ was discussed on the basis of its standard Gibbs energy of formation, Δ_fG^°_m, which was derived by combining S^°_m determined in this study with the reference datum of the standard enthalpy of formation, Δ_fH^°_m. Ag₂MoO₄ was found to exhibit greater phase stability in nuclear fuel waste glasses than transition metal molybdates such as NiMoO₄ and ZrMo₂O₈.

Fig. 1 The experimental molar heat capacities, C^°_p,m, of Ag₂MoO₄(cr) at 2–300 K. Solid line shows C^°_p,m calculated from the fitting functions given by eqs. (2)–(4) and Table 3.