Classical model of negative thermal expansion in solids with expanding bonds

Abstract

We study negative thermal expansion (NTE) in model lattices with multiple atoms per cell and first- and second-nearest neighbor interactions using the (anharmonic) Morse potential. By exploring the phase space of neighbor distances and thermal expansion rates of the bonds, we determine the conditions under which NTE emerges. By permitting all bond lengths to expand at different rates, we find that NTE is possible without appealing to fully rigid units. Nearly constant, large-amplitude, isotropic NTE is observed up to the melting temperature in a classical molecular dynamics model of a ${\mathrm{ReO}}_3$-like structure when the rigidity of octahedral units is almost completely eliminated. Only weak NTE, changing over to positive expansion is observed when the corner-linked octahedra are rigid, with flexible second-neighbor bonds between neighboring octahedra permitting easy rotation. We observe similar changes to thermal expansion behavior for the diamond lattice: NTE when second-neighbor interactions are weak to positive thermal expansion when second-neighbor interactions are strong. From these observations, we suggest that the only essential local conditions for NTE are atoms with low coordination numbers along with very low energies for changing bond angles relative to bond-stretching energies.

arXiv comment7 pages (7 figures) with 1 page (1 figure) supplemental

References in corpus (5)

• Unusual Low-Energy Phonon Dynamics in the Negative Thermal Expansion Compound ZrW2O8
• Framework Flexibility and the Negative Thermal Expansion Mechanism of Copper(I) Oxide, Cu2O
• Phonons, Nature of Bonding and Their Relation to Anomalous Thermal Expansion Behavior of M2O (M=Au, Ag, Cu)
• Dynamics of some constrained lattices
• Local structure of ReO${}_3$ at ambient pressure from neutron total scattering study

Cited by in corpus (3)

• Anharmonicity and scissoring modes in the negative thermal expansion materials ScF${}_3$ and CaZrF${}_6$
• Soft mode anisotropy in negative thermal expansion material ReO${}_3$
• 1D fluids with repulsive nearest-neighbour interactions: Low-temperature anomalies