Thermodynamic and structural properties of PrBaCo2O5+δ

The oxygen content of the double cobaltite PrBaCo2O5+delta was determined by coulometric titration in broad temperature and oxygen pressure ranges, and the partial thermodynamic functions of oxygen were evaluated. The results oil the nonstoichiometry and structural properties of PrBaCo2O5+delta demonstrate that, at 5 + delta < 5.3, this cobaltite has a high-temperature phase with lattice parameters a = 11.774 angstrom, b = 11.932 angstrom, and c = 7.609 angstrom. The cornposition dependences of Delta(H) over bar (O) and Delta(S) over bar (O) indicate that the 3a(p) x 3a(p) x 2a(p) orthorhombic structure persists in the range 5.15 <= 5 + delta <= 5.30. Some of the Co3+ ions are shown to disproportionate according to the scheme 2Co(3+) = Co2+ + CO4+.