Towards the elastic properties of 3D spin-crossover thin films: Evidence of buckling effects

Abstract

This work addresses the macroscopic deformations of spin-crossover (SC) thin sheets upon their cooperative transformation between the low-spin (LS) and the high-spin (HS) states from the viewpoint of electro-elastic interactions among molecules. When the size of each molecule changes depending on its spin state, the elastic interaction among the lattice distortions provides the cooperative interactions between the spin states, resulting in a macroscopic volume change. In this prospective contribution, we study the elasto-electronic properties of SC sheets in which the atoms can move according to the three directions of space. We predict that when HS and LS domains coexist, the system undergoes tremendous strain by compressing and expanding to differing degrees along the sheet, and it becomes far more favourable energetically to the sheet to buckle out of the plane. According to the elastic interaction between the SC atoms, we found the existence of a phase transition between flat and highly crumpled surfaces. This phenomenon was also investigated on two elastically coupled SC membranes where we demonstrate the existence of specific features of electro-elastic HS:LS interface. To enhance the quality of the surface layers, we have implemented the radial basis functions (RBF) interpolation which allowed to study small systems in a very accurate way. This method gives rise to a functional representation of a solid model, where gradients can be determined analytically, thus promising better understanding of the macroscopic crystal deformations and morphologies during the phase transition.