Vaporization of LaCrO 3 : Partial and Integral Thermodynamic Properties

The vaporization of LaCrO 3 (s) and samples of the composition LaCrO 3 + La 2 O 3 was investigated in the temperature range of 1887‐2333 K by Knudsen effusion mass spectrometry using Knudsen cells made of tungsten lined completely with iridium. The species Cr(g), CrO(g ), CrO 2 (g), and LaO(g) were identified in the vapor. Their partial pressures were determined by calibration with pure platinum solid. The thermodynamic activity of Cr 2 O 3 , a cr2 o 3 in LaCrO 3 for the Cr 2 0 3 ‐poor phase boundary of this phase was In a Cr2 o 3 = ‐(17953/T) ‐ 0.485 (temperature T given in K) for the temperature range of the measurements with a probable overall error of ± 13%. The following values and temperature dependence of ΔG° f,T resulted for the formation of LaCrO 3 (s) according to the reaction 0.5Cr 2 O 3 (s) + 0.5La 2 O 3 (s) → LaCrO 3 (s): ΔG° f,2100 = ‐78.9 ± 1.1 kj/mol, Δ H° f,298 = ‐76.8 ± 5.2 kj/mol, and ΔG° r (kJ/mol) = ‐74.7 ‐ 0.00202 T . Computations for the vaporization of LaCrO 3 were conducted to show the volatility of this material in different atmospheres at high temperatures.