The Lu–Ru–O System: Thermodynamic properties and impedance measurements of the pyrochlore Lu2Ru2O7(s)

The Gibbs free energy of formation of Lu2Ru2O7(s) has been determined using solid-state electrochemical technique employing oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following solid-state electrochemical cell has been measured:Cell:(−)Pt/{Lu2O3(s)+Lu2Ru2O7(s)+Ru(s)}//CSZ//O2(p(O2)=21.21 kPa)/Pt(+)Cell:(−)Pt/Lu2O3s+Lu2Ru2O7s+Rus//CSZ//O2pO2=21.21 kPa/Pt+The Gibbs free energy of formation of Lu2Ru2O7(s) from elements in their standard state, calculated by the least squares regression analysis of the data obtained in the present study, can be represented by:{ΔfG°(Lu2Ru2O7,s)/(kJ·mol−1)±2.7}=−2513.7+0.6265·(T/K);943.9£T/K£1230).{ΔfG°Lu2Ru2O7,s/kJ·mol−1±2.7}=−2513.7+0.6265·T/K;943.9£T/K£1230).Standard molar heat capacity C°p,m(T) of Lu2Ru2O7(s), was measured using a heat flux type differential scanning calorimeter (DSC) in two different temperature ranges, from 127 K to 299 K and 307 K to 845 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by:C°p,m(Lu2Ru2O7(s)(J.K−1·mol−1)=294.535+2.0·10−4T(K)−49.00688·105/T2(K).C°p,m(Lu2Ru2O7sJ.K−1·mol−1=294.535+2.0·10−4TK−49.00688·105/T2K.The second law method gave the value of standard enthalpy of formation and entropy, of the compound from elements at 298.15 K. An oxygen potential diagram for the Lu–Ru–O system was computed based on the thermodynamic data obtained. Impedance measurements on Lu2Ru2O7(s), suggests a semiconductor like behavior with low activation energy.

► The pyrochlore oxide Lu2Ru2O7 was synthesized and characterized.
► Thermodynamic parameters of Lu2Ru2O7 has been determined.
► Oxygen potential diagram for the Lu-Ru-O system was established.
► Semiconducting nature of the Lu2Ru2O7 was confirmed.