High pressure synthesis of novel perovskite-type oxides with unusually high valence transition-metal ions

Perovskite oxides with unusually high valence 3d transition metal ions such as Fe4+ and Co4+ show unique magnetism inherent to the strong p-d hybridization. This is exemplified by the nontrivial helimagnetism and ferromagnetism in Rh-doped SrFeO3 [1] and room-temperature ferromagnetism in SrCoO3. However, the search for novel electronic phases in these oxides has been hampered by the difficulty in the sample preparation at high pressures.

In this seminar, after the brief review on structure and physical properties of unusually high valence perovskite-type oxides, we show our recent studies on novel perovskites Sr1-xBaxCoO3 and La1-xPrxCuO3 prepared at high pressures. Sr1-xBaxCoO3 shows a novel helimagnetic phase upon the suppression of the ferromagnetic phase by the Ba doping [2], and the helimagnetic compound is found to show a giant magnetovolume effect. As for La1-xPrxCuO3, we found that the compounds with x larger than 0.6 have highly distorted GdFeO3-type structure containing quasi-one-dimensional Cu-O chains [3]. From the structural and electronic studies combined with first-principles calculations, the oxidation state of Cu in PrCuO3 is found to be close to 2+ rather than 3+. The novel structural and electronic states of these perovskites with unusually high valence Co4+ and Cu3+ ions will be discussed in terms of the interplay between charge, orbital, and lattice in oxides with strong p-d and p-d-f hybridizations.

[1] M. Kinoshita, H. Sakai, N. Hayashi, Y. Tokura, M. Takano, and S. Ishiwata, Angew. Chem. Int. Ed., 55, 15292 (2016).
[2] H. Sakai et al., in preparation.
[3] M. Ito et al., in preparation.