Differential scanning calorimetric measurements and thermodynamic functions of YbRhO₃(s)

Abstract

Standard molar heat capacity, $C_{{\rm{p}},{\rm{m}}}^{\rm{o}}(T)$, of YbRhO₃(s) was determined using a heat flux type differential scanning calorimeter from 126 to 846 K. The heat capacities in the temperature range 307 ≤ T (K) ≤ 846 were fitted into a polynomial expression and can be represented by $C_{{\rm{p}},{\rm{m}}}^{\rm{o}}$ (YbRhO₃, s, T) [J/(K mol)] = 106.82 + 8.57 × 10⁻³T (K) − 9.48 × 10⁵/ T²(K). The standard molar heat capacity of YbRhO₃(s), $C_{{\rm{p}},{\rm{m}}}^{\rm{o}}$, at 298.15 K is 98.7 J/(K mol). The standard molar Gibbs energy of formation of YbRhO₃(s) was also determined using calcia stabilized zirconia as an oxide electrolyte and air as the reference electrode by the solid state electrochemical technique. The cell can be represented by (−)Pt–Rh/{Yb₂O₃(s) + YbRhO₃(s) + Rh(s)}//CSZ//O₂(p (O₂) = 21.21 kPa)/Pt–Rh(+). The electromotive force was measured in the temperature range from 889 to 1110 K. The standard Gibbs energy of formation of YbRhO₃(s) from elements in their standard state can be represented by Δ_fG^o{YbRhO₃(s)}/kJ/mol(±1.62) = −1110.9 + 0.287 T (K). The heat capacity of YbRhO₃(s) was used along with the data obtained from the electrochemical cell to evaluate all thermodynamic functions of YbRhO₃(s).