Thermodynamic study of compounds of the Nd-Ba-Cu-O system

Standard enthalpies of formation for solid solutions of composition Nd1 + x Ba2 − x Cu3O y (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa2Cu3O6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy S o(T), the difference of enthalpies H o(T)-H o(0 K), and the reduced Gibbs energy Φo(T) = S o(T)–[H o(T)–H o(0)]/T were calculated on the basis of smoothed dependence C p (T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd1+x Ba2−x Cu3O y . The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.