Evidence of lattice deformation induced metal-insulator transition in Ti2O3

We synthesized ${\mathrm{Ti}}₂{\mathrm{O}}₃$ epitaxial films with continuously varying ratios of the c-axis to a-axis lattice constants ($c/a$ ratios) on 4H-SiC (0001) substrates and investigated their structural and electronic properties. ${\mathrm{Ti}}₂{\mathrm{O}}₃$ films with a wide range of $c/a$ ratios were fabricated in a controllable fashion by changing the growth temperature. As the $c/a$ ratio at room temperature increased, the metal-insulator transition (MIT) temperature systematically decreased and eventually the MIT disappeared. Detailed analyses revealed that the MIT occurred at a critical $c/a$ ratio of 2.68. The critical $c/a$ ratio for the occurrence of the MIT was also reproduced by density functional theory calculations. These results provide evidence for the origin of the MIT in ${\mathrm{Ti}}₂{\mathrm{O}}₃$. The MIT is not a Mott transition induced by temperature, but a gradual semimetal-to-semiconductor transition induced by lattice deformation.