Structural Manipulation of Phase Transitions by Self-induced Strain in Geometrically Confined Thin Films*

Strain engineering is used very frequently to tune material properties in thin films. The most studied sources of strain are lattice mismatch and differential thermal contraction between the substrate and film. However, we show that in materials which undergo a structural phase transition (SPT), a third and often overlooked source of strain may play a very significant role. If the substrate confines the area of the film, the SPT may induce stress which changes the evolution of the transition. This is a 2D analog of the isochoric water-ice transition, where the freezing point drops below 0°C.
To illustrate this, we use the prototypical Mott insulator V₂O₃ which has a first order SPT coupled to a metal-insulator transition to show how self-induced stress can drastically alter structural and electronic properties. We found means of controlling the magnitude of self-strain by modifying substrate morphology. This effect may be important for many materials which exhibit a first order SPT and are subjected to geometrical constraints.

Kalcheim et al. Adv. Funct. Mater. 2020, 2005939