Formation enthalpies of LaLn'O₃ (Ln'=Ho, Er, Tm and Yb) interlanthanide perovskites

High-temperature oxide melt solution calorimetry using 3Na₂O·MoO₃ at 802 °C was performed for interlanthanide perovskites LaLn'O₃ (Ln'=Ho, Er, Tm and Yb) and lanthanide oxides (La₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃ and Yb₂O₃). The enthalpies of formation of these interlanthanide perovskites from binary lanthanide oxides at room temperature (25 °C) were determined to be −8.3±3.4 kJ/mol for LaHoO₃, −9.9±3.0 kJ/mol for LaErO₃, −10.8±2.7 kJ/mol for LaTmO₃ and −12.3±2.9 kJ/mol for LaYbO₃. There is a roughly linear relationships between these enthalpy values and the tolerance factor for these and for other LaM³⁺O₃ (M=In, Sc, Ga, Al, Fe and Cr) perovskites, confirming that the distortion of the perovskites as results from ionic radius difference of A-site and B-site cations, is the main factor determining the stability of these compounds. - Graphical abstract: A linear relationship between the enthalpy of formation and the tolerance factor for interlanthanide LaLn'O₃ (Ln'=Ho, Er, Tm, and Yb) and other LaM³⁺O₃ (M=In, Sc, Ga, Al, Fe and Cr) perovskites. - Highlights: • Interlanthanide perovskites were synthesized by solid state reactions. • Their enthalpies of formation were measured by oxide melt solution calorimetry. • ΔH_f,ox shows a linear relationship with tolerance factor