Thermodynamic studies on SrThO3(s)

The Gibbs energy of formation of SrThO3(s) has been determined using e.m.f. and manometric techniques. In the e.m.f. method, two fluoride cells have been constructed to determine ΔfG0m(SrThO3,s,T) using CaF2(s) as a solid electrolyte. The cells used are:(−)O2(g),Pt/SrO(s)+SrF2(s)//CaF2//(SrThO3(s)+ThO2(s)+SrF2(s)/Pt,O2(g)(+), (I)(−)O2(g),Pt/SrThO3(s)+SrF2(s)+ThO2(s)//CaF2(s)//CaO(s)+CaF2(s)/Pt,O2(g)(+). (II) served e.m.f. values are represented by following respective expressions:E (V)±0.0001=0.0998+3.254×10−5T (K), (Cell I)E (V)±0.0001=0.0285−6.37×10−5T (K). (Cell II)From the measured e.m.f. values of the cells and the ΔfG0m(T) values from the literature, ΔfG0m(SrThO3,s,T) have been calculated and are respectively given asΔfG0m(SrThO3,s,T)±10 kJ mol−1=−1829.2+0.2735T (K) (978⩽T (K)⩽1154), (Cell I)ΔfG0(SrThO3,s,T)±20 kJ mol−1=−1853.5+0.2867T (K) (1008⩽T (K)⩽1168). (Cell II) manometric technique, equilibrium CO2(g) pressures are measured over the three phase mixture: {SrThO3(s)+SrCO3(s)+ThO2(s)} using a mercury manometer from 1075 to 1197 K. The corresponding Gibbs energy as a function of temperature is given byΔfG0m(SrThO3,s,T)(kJ mol−1)±14=−1865.4+0.3086T (K).