System Er–Ru–O: High temperature study of the heavy rare earth pyrochlore Er2Ru2O7(s) by electrochemical cell and differential scanning calorimeter

Abstract

Abstract The Gibbs free energy of formation of Er 2 Ru 2 O 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: (−)Pt/{Er 2 O 3 (s) + Er 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 Er 2 Ru 2 O 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 given by: {Δ f G°(Er 2 Ru 2 O 7 ,s) / (kJ∙mol −1 ) ± 2.2} = − 2517.3 + 0.6099 ∙ (T/K); (934.6 ≤ T/K ≤ 1236.3). Standard molar heat capacity C° p,m (T) of Er 2 Ru 2 O 7 (s) was measured using a heat flux type differential scanning calorimeter (DSC) in two different temperature ranges, from 129 K to 296 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 (Er 2 Ru 2 O 7 ,s,T)(J∙K −1 ∙mol −1 ) = 293.88 + 2.397 10 −2 T(K) − 54.74717 10 5 /T 2 (K); (307 ≤ T(K) ≤ 845). The heat capacity of Er 2 Ru 2 O 7 (s), was used along with the data obtained from the oxide electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K.