Crystal Structures and Conduction Paths of Sc-Doped CaTiO3 Fast Oxide-Ion Conductors with Orthorhombic Symmetry

Katsuhiro Nomura; Shin-Ichi Hashimoto; Tomoaki Namioka; Hiroaki Kato; Takeshi Hagiwara; Akinori Hoshikawa

doi:10.1021/acs.inorgchem.2c02190

Crystal Structures and Conduction Paths of Sc-Doped CaTiO₃ Fast Oxide-Ion Conductors with Orthorhombic Symmetry

Inorg Chem. 2022 Nov 14;61(45):17985-17992. doi: 10.1021/acs.inorgchem.2c02190. Epub 2022 Oct 31.

Authors

Katsuhiro Nomura¹, Shin-Ichi Hashimoto², Tomoaki Namioka², Hiroaki Kato², Takeshi Hagiwara³, Akinori Hoshikawa⁴

Affiliations

¹ Innovative Functional Materials Research Institute, Department of Materials and Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya463-8560, Japan.
² College of Engineering, Chubu University, Kasugai487-8501, Japan.
³ Research Institute for Engineering, Kanagawa University, Yokohama221-8686, Japan.
⁴ Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Tokai319-1106, Japan.

PMID: 36315044
DOI: 10.1021/acs.inorgchem.2c02190

Abstract

The crystal structures and electron density distributions (EDDs) of Ca-deficient Sc-doped CaTiO₃ fast oxide-ion conductors, Ca_0.97(Ti_0.97Sc_0.03)O_3-δ (CTS3) and Ca_0.96(Ti_0.9Sc_0.1)O_3-δ (CTS10), were investigated in the temperature range of 298-1173 K in N₂ to analyze the effect of composition on the perovskite structure and oxide-ion transport mechanism. CTS3 and CTS10 exhibited orthorhombic Pnma symmetry in temperature ranges of 298-1173 K and 973-1173 K, respectively, with CTS10 exhibiting lower symmetry and reduction in oxide-ion conductivity below 973 K. The EDDs of CTS3 and CTS10 at 1173 K indicated unique chemical bonds and conduction paths. CTS3 and CTS10 showed covalent bonds between (Ti,Sc) and O1 (or O2) sites. CTS3, with a lower oxide-ion conductivity than that of CTS10, exhibited pseudo-one-dimensional (1D) zig-zag curved conduction paths for oxide-ions along the a-axis, unlike previously reported curved migration paths along the b-axis in CaTiO₃, and chemical bonds between Ca and O1 sites, indicating oxide-ion conduction suppression. In CTS10, additional conduction paths were observed along the a-axis, forming three-dimensional (3D) zig-zag curved conduction paths in the ac-plane and along the b-axis, with the weakening of the chemical bonds between the Ca and O1 sites. The oxide-ion conductivity and mobile oxide-ion concentration of CTS10 were 3.6 and 2.0 times those of CTS3, respectively, at 1173 K; the higher oxide-ion conductivity of CTS10 could be attributed to an increase in the mobile oxide-ion concentration and mobility with a 1D to 3D change in the conduction paths and a weakening of chemical bonds between the Ca and O1 sites.