A. S. Monaenkova

Thermochemical characteristics of nonstoichiometric Ba2Cu3O5: II. Thermal transformations

Abstract Thermoanalysis (TG-DSC) of the pure compound Ba2Cu3O5+δ (023) has been carried out at oxygen pressures of 0.21 and 1 atm in the temperature range 25–970°C. It was shown that 5.5 823°C at 0.21 atm O2; > 890°C at 1 atm O2) appeared. The liquid phase transition took place at temperatures higher than 860°C (0.21 atm) and 910°C (1 atm).

Thermodynamic properties and oxygen stoichiometry of Ba2Cu3O5 + δ

The thermodynamic properties and oxygen stoichiometry of Ba2Cu3O5 + δ are studied by means of the electromotive force (EMF) with a fluoride electrolyte, dissolution calorimetry, and thermogravimetry. It is shown that the temperature dependence of the Gibbs energy of the formation of barium cuprate from simple oxides and oxygen in the temperature range of 860–1120 K can be described by the polynomial Δf, oxG∘(Ba2Cu3O5 + δ) ± 0.1 (kJ/mol) = −291.78 + 1.127T − 0.13207 TlnT (kJ/mol).

Thermochemical characteristics of reactions of calcium with perchloric acid

The enthalpy of reaction of metallic calcium with perchloric acid was measured for the first time in a sealed swinging calorimeter equipped with an isothermal shell. Standard enthalpies of formation of calcium ion in an infinitely diluted aqueous solution (−542.8 ± 1.0 kJ/mol) and calcium chloride in crystal state (−794.9 ± 1.0 kJ/mol) were calculated according to the results obtained with the use of published data.

The enthalpies of formation of Sm1 + xBa2 − xCu3Oy substitution solid solutions

The enthalpies of reactions of Sm1 + xBa2 − xCu3Oy substitution solid solutions (x = 0, 0.1, 0.2, 0.3, 0.7, and 0.8) with 1.07 N HCl were measured at 298.15 K in a hermetic isothermic-shell swinging calorimeter. The results and the literature data were used to calculate the standard enthalpies of their formation from simple substances and binary oxides (ΔfH298.15o and ΔoxH298.15o). The dependence of the enthalpy of formation on the degree of samarium substitution for barium was obtained.

Thermochemical properties of Ln2BaCoO5 (Ln = Nd, Gd, Dy, Ho)

The enthalpies of the reactions of double rare-earth and barium cobaltites Ln2BaCOO5 (Ln = Nd, Gd, Dy, Ho) and metallic dysprosium with 1 M hydrochloric acid are measured at 298.15 K using precision calorimetric equipment. The standard enthalpies of formation of Ln2BaCoO5 from simple components and binary oxides were calculated from the obtained results and reliable literature data.