Nanoscale effects on the stability of the λ-Ti₃O ₅ polymorph

The nanocrystalline valency-delocalized λ-phase of the binary oxide Ti₃O₅ has recently emerged as a promising phase-change material that exhibits rapid photo-reversible optical and resistance changes at ambient temperature. Nanoscaling caused the monoclinic-λ to monoclinic charge-ordered β-phase structural instability to shift to considerably lower temperatures compared to the bulk material, and led to a broad thermal hysteresis. The structural transformation was accompanied by a large change in volume and large lattice relaxations, which imply the presence of strong electron-phonon coupling. We attribute the suppression of the phase transition to the enhanced surface energy on the nanoscale.