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

Аннотация

The XANES spectra (X-ray absorption near-edge spectra) at the K edge of Co and the L₃ edge of Gd in polycrystalline Gd_0.4Sr_0.6CoO_{3 – 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 Gd_0.4Sr_0.6CoO_2.85 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.