Spin states of cobalt and the thermodynamics of Sm1-xCaxCoO3-δ solid solutions

In the rare-earth SmCoO3 perovskite, Co3+ ions at low temperatures appear to be in the low-spin state with S = 0, t (2g) (2) e (g) (0) . If Ca2+ ions partially substitute Sm3+ ions, oxygen deficient Sm1 - x Ca (x) CoO3 - delta solid solutions with delta = x/2 appear. The oxygen deficiency leads to the formation of pyramidally coordinated cobalt ions Co (pyr) (3+) in addition to the existing cobalt ions Co (oct) (3+) within the oxygen octahedra. Even at low temperatures, these ions have a magnetic state, either S = 1, t (2g) (5) e (g) (1) or S = 2, t (2g) (4) e (g) (2) . At low temperatures, the magnetization of Sm1 - x Ca (x) CoO3 - delta is mainly determined by the response of Co (pyr) (3+) ions. Owing to the characteristic features of the crystal structure of the oxygen deficient perovskite, these ions form a set of nearly isolated dimers. At high temperatures, the magnetization of Sm1 - x Ca (x) CoO3 - delta is mainly determined by the response of Co (oct) (3+) ions, which exhibit a tendency to undergo the transition from the S = 0, t (2g) (6) e (g) (0) state to the S = 1, t (2g) (5) e (g) (1) or S = 2, tt (2g) (4) e (g) (2) state. In addition, the magnetization and specific heat of the solid solutions under study include the contribution from the rare-earth subsystem, which undergoes a magnetic ordering at low temperatures. DOI: 10.1134/S002136401301013X