Rigidity and mechnisms in negative thermal expansion materials*

Negative thermal expansion (NTE), or a material's tendency to shrink when heated, is an unusual phenomenon which defies intuition. For the type of NTE driven by intrinsic fluctuations of the lattice, we attempt to put this phenomenon in context by exploring a 2D lattice model often cited in NTE papers which is based on rigid molecules flexibly linked where they join and possessing a single collective degree of freedom. We consider carefully the classical, quantum, and thermal consequences of this conceptually simple model and attempt to apply it to real materials to show the limits and benefits of the approach.
[1] Sahan U. Handunkanda, Connor A. Occhialini, Ayman H. Said, and Jason N. Hancock, Two-dimensional nanoscale correlations in the strong negative thermal expansion material ScF3, Physical Review B, 94, 214102 (2016)
[2] Connor A. Occhilaini, Sahan U. Handunkanda, Erin B. Curry, Jason N. Hancock,
Classical, quantum, and thermodynamics of a model exhibiting structural negative thermal expansion, Physical Review B, 95, 094106 (2017)