The Lu–Ru–O System: Thermodynamic properties and impedance measurements of the pyrochlore Lu 2Ru 2O 7(s)

Abstract

The Gibbs free energy of formation of Lu 2Ru 2O 7(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 / Lu 2 O 3 s + Lu 2 Ru 2 O 7 s + Ru s / / CSZ / / O 2 p O 2 = 21 . 21 kPa / Pt + The Gibbs free energy of formation of Lu 2Ru 2O 7(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: { Δ f G ° Lu 2 Ru 2 O 7 , s / kJ · mol − 1 ± 2 . 7 } = − 2513 . 7 + 0. 6265 · T / K ; 943 . 9 £ T / K £ 123 0 ) . Standard molar heat capacity C° p,m( T) of Lu 2Ru 2O 7(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 ( Lu 2 Ru 2 O 7 s J . K − 1 · mol − 1 = 294 . 535 + 2 .0 · 1 0 − 4 T K − 49 .00 688 · 1 0 5 / T 2 K . 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 Lu 2Ru 2O 7(s), suggests a semiconductor like behavior with low activation energy.