The role of defects in microwave and conventionally synthesized LaCoO3 perovskite

Abstract

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Microwave-Assisted Synthesis, Microstructure, and Magnetic Properties of Rare-Earth Cobaltites

“…These Co 2+ cations constitute magnetic impurities, which have been shown recently to act as nucleation centers for the formation of higher spin states across the spin-state transition [11]. However, the weight loss measured here indicated that possible oxygen vacancies in all synthesized powder samples would exhibit a small concentration below the resolution limit of the TGA balance.…”

“…The Co 3+ spin states may be (a) low-spin (LS) (t2g 6 eg 0 ), (b) intermediate-spin (IS) (t2g 5 eg 1 ), or (c) high-spin (HS) (t2g 4 eg 2 ) [10][11][12]. The competition between different spin states has caused large controversy in the literature previously [10,[12][13][14][15][16][17][18][19], but in most studies only the case of LaCoO3 has been considered.…”

“…Here we show that monophasic rare-earth cobaltite materials can be obtained by MWassisted synthesis within 30 minutes with massive time and energy savings. LaCoO3 has been synthesized previously by innovative and novel chemical synthesis methods [28][29][30], including MW-assisted processes [11,31,32], but the rest of the series (RE = Pr -Dy) has not been prepared before using MW heat sources to the best of our knowledge.…”

“…Furthermore, we show that the magnetism in microwave (MW) synthesized (RE)­CoO 3 displays different types of magnetic ordering, , which depends on the RE cation and involves variation of the Co 3+ spin state (electronic configuration: Ar 3d 6 ). The Co 3+ spin states may be (a) low-spin (LS) (t 2 g 6 e g 0 ), (b) intermediate-spin (IS) (t 2 g 5 e g 1 ), or (c) high-spin (HS) (t 2 g 4 e g 2 ). − The competition between different spin states has caused large controversy in the literature previously, ,− but in most studies, only the case of LaCoO 3 has been considered. Different studies favor either an LS to IS or an LS to HS state transition by heating across T s1 ≈ 75 K. − Furthermore, a low temperature magnetic defect structure has been commonly observed in La­CoO 3 , which can be explained by the existence of magnetic polarons or excitons. − Here in this work, we investigate the influence of the RE cation on the structural, microstructural, and magnetic properties, in particular on the Co 3+ spin state, the spin-state transition, and the magnetic defect structure.…”

“…Here, we show that single phase rare-earth cobaltite materials can be obtained by MW-assisted synthesis within 30 min with massive time and energy savings. La­CoO 3 has been synthesized previously by innovative and novel chemical synthesis methods, − including MW-assisted processes, ,, but the rest of the series (RE = Pr–Dy) has not been prepared before using MW heat sources to the best of our knowledge. In ref , we had shown that the MW synthesis process in La­CoO 3 leads to the same crystallographic R 3̅ c orthorhombic perovskite phase as compared to conventional synthesis, and only small quantitative variations in the magnetism and charge transport properties had been detected.…”