The ruthenium pyrochlore Dy2Ru2O7(s): Stability and calorimetry

Abstract

The 4d transition metal ruthenium pyrochlore Dy2Ru2O7(s) was synthesized by solid state reaction route. High temperature studies on the ternary oxide Dy2Ru2O7(s) an important ferroelectric and magnetic material, has been carried out using solid-state electrochemical cell, with calcia stabilized zirconia electrolyte and the reversible electromotive force were measured. The Gibbs energy of formation of Dy2Ru2O7(s) from elements in their standard state, is: $$ \begin{aligned} \{ \Delta_{\text{f}} G^{ \circ } ({\text{Dy}}_{2} {\text{Ru}}_{2} {\text{O}}_{7} ,{\text{s}}) /({\text{kJ mol}}^{ - 1} ) \pm 4.4\} & = - 2505.0 + 0.627 \cdot \left( {T/{\text{K}}} \right); & \quad (859 \le T / {\text{K}} \le 1136). \end{aligned} $$ The standard molar heat capacity C˚p,m(T) of Dy2Ru2O7(s), measured using a differential scanning calorimeter run in the heat flux mode as a function of temperature. The values fitted to a polynomial expression can be represented by: $$ C_{{{\text{p}},{\text{m}}}}^{ \circ } \,({\text{Dy}}_{2} {\text{Ru}}_{2} {\text{O}}_{7} ,{\text{s}},T)\,({\text{J K}}^{ - 1} \, {\text{mol}}^{ - 1} ) = 235.09 + 3.99 \times 10^{ - 2} T({\text{K}}) - 10.53 \times 10^{5} / {\text{T}}^{2} ({\text{K}}). $$ Stability of Dy2Ru2O7(s) and high temperature thermodynamic functions of this transition metal pyrochlore were determined for the first time, an important fundamental study.