Robust Giant Tetragonal Distortion Coupled with High-Spin Co3+ in Electron-Doped BiCoO3

Hayato Ishizaki; Hajime Yamamoto; Takumi Nishikubo; Yuki Sakai; Shogo Kawaguchi; Keisuke Yokoyama; Yoichi Okimoto; Shin-Ya Koshihara; Takafumi Yamamoto; Masaki Azuma

doi:10.1021/acs.inorgchem.9b02381

Robust Giant Tetragonal Distortion Coupled with High-Spin Co³⁺ in Electron-Doped BiCoO₃

Inorg Chem. 2019 Dec 2;58(23):16059-16064. doi: 10.1021/acs.inorgchem.9b02381. Epub 2019 Nov 12.

Authors

Hayato Ishizaki¹, Hajime Yamamoto², Takumi Nishikubo¹, Yuki Sakai^{1

3}, Shogo Kawaguchi⁴, Keisuke Yokoyama⁵, Yoichi Okimoto⁵, Shin-Ya Koshihara⁵, Takafumi Yamamoto¹, Masaki Azuma^{1

3}

Affiliations

¹ Laboratory for Materials and Structures , Tokyo Institute of Technology , 4259 Nagatsuta , Midori, Yokohama 226-8503 , Japan.
² Institute of Multidisciplinary Research for Advanced Materials , Tohoku University , 2-1-1 Katahira , Aoba-ku, Sendai 980-8577 , Japan.
³ Kanagawa Institute of Industrial Science and Technology , 705-1 Shimoimaizumi , Ebina, Kanagawa 243-0435 , Japan.
⁴ Diffraction and Scattering Division , Japan Synchrotron Radiation Research Institute, SPring-8 , 1-1-1 Kouto, Sayo-cho , Sayo-gun, Hyogo 679-5198 , Japan.
⁵ Department of Chemistry , Tokyo Institute of Technology , 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8551 , Japan.

PMID: 31714758
DOI: 10.1021/acs.inorgchem.9b02381

Abstract

BiCoO₃ is a PbTiO₃ type of perovskite oxide with a giant tetragonal distortion (c/a = 1.27) that shows a pressure-induced transition from tetragonal to orthorhombic phases accompanied by a large volume shrinkage at 3 GPa. In this study, we carried out electron doping of BiCoO₃ by substituting Ti⁴⁺ for Co³⁺ in order to destabilize the tetragonal phase and observe a giant negative thermal expansion (NTE) at ambient pressure. BiCo_1-xTi_xO₃ (x = 0, 0.1, 0.2, and 0.25) was successfully obtained by using high-pressure synthesis. However, the c/a ratio of the tetragonal phase was almost constant against x (≤0.2), and NTE was not observed at any x, suggesting that the tetragonal distortion coupled with high-spin Co³⁺ is robust against electron doping. In x = 0.25, a metastable orthorhombic phase was obtained by the high-pressure synthetic process, while it partially transformed into a tetragonal phase after annealing at 600 K. The stability of the giant tetragonal phase is strongly connected with the spin state of Co³⁺.