Synthesis of nanosize tetratitanium heptoxide and its anomalous phase transition

Abstract

Tetratitanium heptoxide, Ti4O7, is known to exhibit a two-step phase transition from the charge-delocalized to charge-localized phase and the charge-disordered to charge-ordered phase around 150 K and 130 K, respectively. Herein, a nanoscopic effect of the Ti4O7 phase transition is studied. A one-step phase transition from the charge-delocalized to charge-localized phase is realized in Ti4O7 nanocrystals where the transition from the charge-disordered to charge-ordered phase is suppressed. Perturbation to the free energy by the surface energy can explain this anomalous phase transition. The present nanoscopic effect, which can control cooperativity in phase transitions, should contribute to develop advanced switching materials. Impact statement: Ti4O7 nanocrystal exhibits a one-step phase transition from a charge-delocalized to a charge-localized phase. This anomalous phase transition can be understood by the nanoscopic effect contributed by the surface energy.