Perovskite-Type InCoO3 with Low-Spin Co(3+): Effect of In-O Covalency on Structural Stabilization in Comparison with Rare-Earth Series

Koji Fujita (1) , Takahiro Kawamoto (1) , Ikuya Yamada (2, 3) , Olivier Hernandez (4) , Hirofumi Akamatsu (5) , Yu Kumagai (5) , Fumiyasu Oba (5) , Pascal Manuel (6) , Ryo Fujikawa (1) , Suguru Yoshida (1) , Masayuki Fukuda (1) , Katsuhisa Tanaka (1)

1 Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
2 IMPMC - Institut de minéralogie et de physique des milieux condensés
3 Osaka Prefecture University
4 ISCR - Institut des Sciences Chimiques de Rennes
5 TITECH - Tokyo Institute of Technology [Tokyo]
6 ISIS Facility

Perovskite rare-earth cobaltites ACoO3 (A = Sc, Y, La-Lu) have been of enduring interest for decades due to their unusual structural and physical properties associated with the spin-state transitions of low-spin Co(3+) ions. Herein, we have synthesized a non-rare-earth perovskite cobaltite, InCoO3, at 15 GPa and 1400 °C and investigated its crystal structure and magnetic ground state. Under the same high-pressure and high-temperature conditions, we also prepared a perovskite-type ScCoO3 with an improved cation stoichiometry in comparison to that in a previous study, where synthesis at 6 GPa and 1297 °C yielded a perovskite cobaltite with cation mixing on the A-site, (Sc0.95Co0.05)CoO3. The two perovskite phases have nearly stoichiometric cation compositions, crystallizing in the orthorhombic Pnma space group. In the present investigation, comprehensive studies on newly developed and well-known Pnma ACoO3 perovskites (A = In, Sc, Y, Pr-Lu) show that InCoO3 does not fulfill the general evolution of crystal metrics with A-site cation size, indicating that InCoO3 and rare-earth counterparts have different chemistry for stabilizing the Pnma structures. Detailed structural analyses combined with first-principles calculations reveal that the origin of the anomaly for InCoO3 is ascribed to the A-site cation displacements that accompany octahedral tilts; despite the highly tilted CoO6 network, the In-O covalency makes In(3+) ions reluctant to move from their ideal cubic-symmetry position, leading to less orthorhombic distortion than would be expected from electrostatic/ionic size mismatch effects. Magnetic studies demonstrate that InCoO3 and ScCoO3 are diamagnetic with a low-spin state of Co(3+) below 300 K, in contrast to the case of (Sc0.95Co0.05)CoO3, where the high-spin Co(3+) ions on the A-site generate a large paramagnetic moment. The present work extends the accessible composition range of the low-spin orthocobaltite series and thus should help to establish a more comprehensive understanding of the structure-property relation.

Domaines: Chimie

Koji Fujita, Takahiro Kawamoto, Ikuya Yamada, Olivier Hernandez, Hirofumi Akamatsu, et al.. Perovskite-Type InCoO3 with Low-Spin Co(3+): Effect of In-O Covalency on Structural Stabilization in Comparison with Rare-Earth Series. Inorganic Chemistry, 2017, 56 (18), pp.11113-11122. ⟨10.1021/acs.inorgchem.7b01426⟩. ⟨hal-01617946⟩