Thermodynamic characterization of lanthanum tellurate

The standard Gibbs energy of formation of lanthanum tellurate, La2TeO6 was derived from its vapour pressure measurements in the temperature range 1420-1520 K employing TG based transpiration method. The temperature dependence of vapour pressure of TeO2 vapour over the mixture La2TeO6 (s) + La2O3 (s) generated by the incongruent vapourisation reaction, La2TeO6(s)→La2o3(s)+TeO2(g)+1/2O2(g) could be represented as: log p (Pa) = [18.47-27127/T (K)] ± 0.03 (1420-1520 K). Enthalpy increments on La2TeO6 were determined by using inverse drop calorimetry in the temperature range 583-1287 K and the thermodynamic functions, namely, heat capacity, entropy and Gibbs energy functions were derived. The mean value of -2381.3 ± 2.0 kJ mol-1 was obtained for ΔfH2980 (La2TeO6) by combining the value of ΔfG0 (La2TeO6) derived from vapour pressure data and the free energy functions of La2TeO6 derived from the drop calorimetry data.