Enthalpy of formation of Ln2O2CO3 II (Ln = La, Nd, Eu) and thermodynamics of decomposition equilibria

High temperature oxide melt solution calorimetry using molten 2PbO center dot B2O3 at 1078 K and molten 3Na(2)O center dot 4MoO(3) at 976 K has been applied to determine standard enthalpies of formation, Delta H-f(m)degrees (298 K), of Ln(2)O(2)CO(3) II (Ln=La, Nd, Eu) from their oxide components Ln(2)O(3) and CO2 at 298 K. Two solvents were applied to cross-check the thermodynamic cycles. Using molten 2PbO center dot B2O3, Delta H-f(m)degrees (298 K) for La2O2CO3 II, Nd2O2CO3 II and Eu2O2CO3 II were found as -198.0 +/- 1.7, -176.2 +/- 3.1 and -151.4 +/- 6.5 kJ mol(-1), respectively. Using molten 3Na(2)O center dot 4MoO(3) the corresponding values for Nd2O2CO3 II and Eu2O2CO3 II were determined as -176.6 +/- 3.5 and -154.9 +/- 3.2 kJ mol(-1), respectively. These enthalpies of formation are discussed in view of prior thermodynamic data, discrepancies are analyzed, and recommended values for enthalpy, entropy and free energy of formation for La2O2CO3 and Nd2O2CO3 are given. (C) 2012 Elsevier B.V. All rights reserved.