Low-Temperature Schottky Anomalies and the Magnetic State of the p Electrons of Oxygen in Substituted Gd0.4Sr0.6CoO3-delta Cobaltites

Orlov, Yu. S.; Dudnikov, V. A.; Platunov, M. S.; Gorev, M. V.; Velikanov, D. A.; Kazak, N. V.; Gavrilkin, S. Yu.; Solov'ev, L. A.; Veligzhanin, A. A.; Vereshchagin, S. N.; Ovchinnikov, S. G. JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 126 (2):217-223; 10.1134/S1063776118020036 FEB 2018

The XANES spectra (X-ray absorption near-edge spectra) at the K edge of Co and the L3 edge of Gd in polycrystalline Gd0.4Sr0.6CoO3 – δ rare-earth oxides with an ordered and disordered distribution of Gd3+ and Sr2+ cations over the A sites in the crystal lattice are measured. The results of XANES measurements do not reveal a noticeable shift in the absorption edge with increasing Sr concentration as compared to the GdCoO3 parent composition. The measured temperature dependences of the heat capacity of polycrystalline ordered and disordered samples and a single-crystal ordered Gd0.4Sr0.6CoO2.85 sample exhibit two Schottky anomalies. These anomalies are thought to be related to the high-spin state of the Co3+ ions in the pyramidal environment caused by oxygen deficiency and to the magnetic state of oxygen p electrons induced by the doping-assisted generation of a hole in the 2p state. The absence of a noticeable shift in the absorption edge and the presence of two Schottky anomalies support the fact that the charge state of cobalt remains unchanged in the compounds under study.