Formation enthalpies of tetravalent lanthanide perovskites by high temperature oxide melt solution calorimetry

High-temperature oxide melt solution calorimetry was used to measure formation enthalpies for several compositions of perovskites of nominal stoichiometry BaPrO₃ and BaCeO₃. Samples were synthesized from chemical solution methods followed by calcination at 1100-1300 °C. PrO₂ was synthesized by oxidation of Pr₆O₁₁ in an oxygen flow at 280 °C. The samples were characterized by microprobe, thermogravimetric and differential thermal analyses. Cell parameters were refined by the Rietveld method. Barium excess in the samples with respect to ideal stoichiometry was detected. Drop solution enthalpies were measured in a Calvet type twin microcalorimeter, using 3Na₂Ȯ4MoO₃ solvent at 702 °C. Preliminary values of the formation enthalpy of BaPrO₃ and BaCeO₃ from oxides were -70 ± 10 kJ/mol and -51 ± 10 kJ/mol, respectively. They fall on the normal trend of energetics versus Goldschmidt tolerance factor and do not show any special stabilization of BaPrO₃ relative to other MLnO₃ perovskites.