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: 5SrThO ₃(s)+W(s)=Sr ₂WO ₅(s)+5ThO ₂(s)+3Sr(g), 1670< T/K<2040, 4SrThO ₃(s)+W(s)=SrWO ₄(l)+4ThO ₂(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 SrThO ₃(s) derived from the vapor pressure data could be represented by Δ f G 0 ( SrThO 3 ( s )) (±5.0 kJ mol −1 )=−1953.6+0.367·T , (1670< T/K<2040) Δ f G 0 ( SrThO 3 ( s )) (±7.0 kJ mol −1 )=−1960.2+0.369·T , (2135< T/K<2420).