Determination of thermodynamic properties of the ternary oxides in the Y-Ru-O system by electromotive force measurements and differential scanning calorimetric measurements

Abstract

In this study, the standard molar Gibbs energy of formation of Y2Ru2O7(s) and Y3RuO7(s) was determined using calcia-stabilized zirconia (CSZ) as an electrolyte and air as a reference electrode. The cells can be represented by: (−)Pt/{Y2O3(s) + Y2Ru2O7(s) + Ru(s)}//CSZ//O2(p(O2) = 21.21 kPa)/Pt(+), (−)Pt/{Y3RuO7(s) + Y2Ru2O7(s) + Y2O3(s)}//CSZ//O2(p(O2) = 21.21kPa)/Pt(+). The electromotive force was measured in the temperature range from 981 to 1155 K and 932 to 1186 K, respectively. The standard molar Gibbs energy of formation of Y2Ru2O7(s) and Y3RuO7(s) from elements in their standard state was calculated by the least squares regression analysis of the data obtained in the present study and can be given, respectively, by: {ΔfG(Y2Ru2O7, s)/(kJmol−1) ± 2.22} = − 2554.1 + 0.625 ⋅ (T/K) and {ΔfG(Y3RuO7, s)/(kJmol−1) ± 2.45} = − 3249.5 + 0.635 ⋅ (T/K). The standard molar heat capacity Cop,m(T) of Y2Ru2O7(s) was measured using a heat flux–type differential scanning calorimeter (DSC) in the temperature range, from 307 to 780 K. The heat capacity was fitted into a mathematical expression and can be represented by: Cp, m(Y2Ru2O7, s, T)(JK−1mol−1) = 256.1 + 5.88 ∙ 10−2T(K) − 34.75 ∙ 105/T2(K). (307 ≤ T (K) ≤ 780). The heat capacity of Y2Ru2O7(s) was used along with the data obtained from the electrochemical cell to determine its decomposition temperature and stability in air and to calculate other thermodynamic parameters.