Thermodynamic properties of SrRuO 3(s)

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The enthalpy increment measurements and the standard molar Gibb’s energy of formation of SrRuO 3(s) were measured using a high-temperature Calvet micro-calorimeter and a galvanic cell, respectively. The enthalpy increments can be represented by the polynomial expression: H 0( T)− H 0(298.15 K) (J mol −1)=−43517.2+120.8 T (K)+0.898×10 −2 T 2 (K)+19.97×10 5/ T (K) [SrRuO 3(s), 310.4≤ T (K)≤798.8]. The heat capacity C 0 p,m( T), the first differential of H 0( T)− H 0(298.15 K) with respect to temperature is given by: C 0 p,m (SrRuO 3, s, T) (J mol −1 K −1)=120.8+1.796×10 −2 T (K)−19.97×10 5/ T 2 (K). The standard Gibbs energy of formation of SrRuO 3(s) has been determined by a galvanic cell using CaF 2(s) as the solid electrolyte. The fluoride cell is represented by: (−)Pt/O 2(g), {CaO(s)+CaF 2(s)}//CaF 2//{SrF 2(s)+RuO 2(s)+SrRuO 3(s)}, O 2(g)/Pt(+). The electromotive force (emf) of the above cell was measured as a function of temperature in the range from 894.4 to 1098 K. The standard Gibb’s energy of formation of SrRuO 3(s) from elements in their standard state obtained by the fluoride cell can be given by: Δ f G 0[SrRuO 3(s)]/kJ mol −1(±2)=−941.0+0.2586·( T/K) (894.4< T/K<1098). The slope and intercept of the above equation gives the entropy and enthalpy of formation of the compound at the average experimental temperature T av=996.2 K. The heat capacity of SrRuO 3(s) determined by Calvet calorimeter and the data obtained from fluoride cell were used to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K. The second law method gives Δ f H 0[SrRuO 3(s), 298.15 K] and Δ f S 0[SrRuO 3(s), 298.15 K] of the compound from elements in their standard state to be −955.0 kJ mol −1 and 111.04 J K −1 mol −1, respectively.