Thermodynamic stability of LuRhO3 in a photoelectrochemical cell

Stability of the pyrochlore Tm2Ru2O7(s) & comparison of its stability with other heavy rare earth ruthenium pyrochlores

Trends in stability of rare earth pyrochlores in the lanthanide series: Ruthenium

The Gibbs energy of formation of Ho2Ru2O7(s) has been determined by employing a solid-state electrochemical cell incorporating an oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following cell has been measured: cell: (−)Pt/{Ho2O3(s) + Ho2Ru2O7(s) + Ru(s)}//CSZ//O2(p(O2) = 21.21 kPa)/Pt(+). The Gibbs energy of formation of Ho2Ru2O7(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: {ΔfG°(Ho2Ru2O7,s)/(kJ mol−1) ± 2.6} = −2518.6 + 0.6225(T/K); (937 ≤ T/K ≤ 1265). The standard molar heat capacity C°p,m(T) of Ho2Ru2O7(s), was measured using a heat flux type differential scanning calorimeter (DSC) in the temperature range from 307 K to 765 K. The heat capacity was fitted into a mathematical expression and can be represented by: C°p,m((Ho2Ru2O7,s,T) (J K−1 mol−1)) = 289.8 + 3.06 × 10−2T (K) − 33.74 × 105/T2 (K); (307 ≤ T (K) ≤ 765). The heat capacity data of Ho2Ru2O7(s), along with the data obtained from the oxide electrochemical cell were used to calculate the standard enthalpy of formation and absolute molar entropy of the compound.

The rare earth ruthenium pyrochlore Ho2Ru2O7(s): thermodynamic properties by electrochemical cell and differential scanning calorimetric measurements

The Gibbs energy of formation of LuRhO3(s) has been determined using a solid-state electrochemical technique employing an oxide ion conducting electrolyte. The Gibbs energy of formation of LuRhO3(s) from elements in their standard state calculated from the data obtained can be represented by: {ΔfGo(LuRhO3, s)/(kJ mol−1) ± 1.35} = −1164.3 + 0.2685(T/K) (943 ≤ T/K ≤ 1121). The standard enthalpy of formation and entropy of the compound at 298.15 K has been derived following the second law method. The standard molar heat capacity of LuRhO3(s) was determined from 128 K to 846 K using a heat flux type differential scanning calorimeter. Based on the thermodynamic data for the compound, an oxygen potential diagram for the Lu–Rh–O system was computed. Impedance measurements on LuRhO3(s), suggests a semiconductor like behavior with low activation energy.

A. R. Joshi

Papers

The rare earth ruthenium pyrochlore Ho2Ru2O7(s): thermodynamic properties by electrochemical cell and differential scanning calorimetric measurements

Thermodynamic stability and impedance measurements of perovskite LuRhO3(s) in the Lu–Rh–O system