Thermodynamic stability of solid SrThO3

The Gibbs energy of formation of strontium thorate was determined by the Knudsen effusion forward collection technique. The evaporation process from a mixture of tungsten and strontium thorate in the Knudsen cell could be represented by the following heterogeneous equilibria: 5SrThO3(s)+W(s)=Sr2WO5(s)+5ThO2(s)+3Sr(g), 1670<T/K<2040, 4SrThO3(s)+W(s)=SrWO4(l)+4ThO2(s)+3Sr(g), 2135<T/K<2420. The measured equilibrium vapor pressures of Sr(g) over the respective temperature regions are given by, ln(p/Pa) (±0.21)=−44419.9/T+23.67, (1670<T/K<2040), ln(p/Pa) (±0.09)=−50009.0/T+25.71, (2135<T/K<2420). The standard Gibbs energy of formation of SrThO3(s) derived from the vapor pressure data could be represented by ΔfG0 (SrThO3(s)) (±5.0 kJ mol−1)=−1953.6+0.367·T, (1670<T/K<2040) ΔfG0 (SrThO3(s)) (±7.0 kJ mol−1)=−1960.2+0.369·T, (2135<T/K<2420).