Metallic ground states of undoped Ti2O3 films induced by elongated c-axis lattice constant

K Yoshimatsu,Y Ishii,Y Nambu,N Hasegawa,Y Wakabayashi,H Kumigashira

doi:10.1038/s41598-020-79182-5

Abstract

Ti2O3 exhibits unique metal–insulator transition (MIT) at ~ 450 K over a wide temperature range of ~ 150 K. The close relationship between MIT and crystal deformation has been proposed. However, as physical properties are governed by the thermodynamic equilibrium in bulk systems, conducting experimental studies under different lattice deformations remains challenging. Epitaxial thin films can offer high flexibility to accommodate adaptive crystal lattices and provide efficient platforms for investigating the MIT. In this study, we report the synthesis of corundum-type Ti2O3 films on various growth temperatures. We found that the metallic ground states appeared in the films grown at low temperatures. The electronic ground states were further investigated by the electronic-structure calculations. Results suggest that the electrical properties of Ti2O3 films were governed by the c/a ratio of the crystal structure, and the absence of the MIT was attributed to the lattice deformation characterized by an elongated c lattice constant.

Highlights

Ti2O3 with a corundum-type crystal structure exhibits unique metal–insulator transition (MIT)
Considering the close relationship between the c/a ratio and MIT observed in the bulk system, it can be presumed that the suppression of the insulating states in the films is related to the lattice deformations
To investigate the relationship between c/a ratios and MIT in T i2O3, we demonstrate another approach to control the lattice deformation in Ti2O3 films, which involves different growth temperatures to manipulate domain sizes and thereby different c/a ratios

Summary

Introduction

Ti2O3 with a corundum-type crystal structure exhibits unique metal–insulator transition (MIT). These results suggest that the LT-Ti2O3 film exhibits corundum-type crystal structures and its electronic structures are similar to those in bulk T i2O3 at high temperatures.

Results

Conclusion