Suppression of the metal-to-semiconductor transition in nanocrystalline Ti4O7via crystallite size control

Abstract

Nanocrystalline Ti₄O₇ with controlled crystallite sizes was synthesized to investigate the effect of crystallite size on the metal–semiconductor transition. Magnetic susceptibility measurements revealed that the transition fraction for Ti₄O₇ with an average crystallite size of 11 nm was approximately 60% of that observed for Ti₄O₇ with a crystallite size of 30 nm, indicating suppression of the phase transition. Differential scanning calorimetry (DSC) showed that the observed transition enthalpies were 302 J mol⁻¹ and 850 J mol⁻¹ for the smaller and larger crystallite sizes, respectively, showing a reduction in the transition enthalpy with decreasing crystallite size. Thermodynamic calculations suggest that this suppression arises from surface energy contributions, which reduce the transition enthalpy with decreasing crystallite size. These results indicate that reducing the crystallite size offers an effective means of controlling the metal–semiconductor transition in Ti₄O₇, contributing to the development of tunable phase-transition materials for advanced functional materials.