Auxetic-Inspired Honeycomb Macrostructures With Anomalous Tailormade Thermal Expansion Properties Including “Negative” Heat-Shrinking Characteristics

Negative thermal expansion (NTE) materials and structures exhibit the anomalous property of shrinking rather than expanding when heated. This work examines the potential of multi-material planar re-entrant and non-re-entrant honeycombs to exhibit anomalous thermal expansion properties. Expressions for the coefficient of thermal expansion as a function of the geometric parameters and intrinsic thermal expansion properties were derived for any in-plane direction. It was shown that re-entrant honeycombs, a metamaterial which is well known for its auxetic characteristics, can be made to exhibit NTE in specific directions when constructed from conventional positive thermal expansion (PTE) materials, provided that the slanting ligaments expand more than the vertical ligaments when heated and that the geometry is amenable. Conversely, it was shown that the construction of such honeycombs from NTE components will not necessarily result in a system which exhibits NTE in all directions. Furthermore, conditions which result in honeycombs demonstrating zero thermal expansion (ZTE) coefficients in specific directions were also explored.

Thermal Expansion Behavior in the A2M3O12 Family of Materials

Over the past several decades, research on anomalous thermal expansion materials has been rapidly growing, and increasing numbers of compounds exhibiting negative thermal expansion (NTE) have been reported. In particular, compounds with formula A2M3O12 have attracted considerable attention. A2M3O12 family materials offer a wide range of possible compositions due to the chemical flexibility of the A and M sites. According to published research, more than half of them possess NTE properties. This paper reviews the range of physical properties displayed by materials in the A2M3O12 family. Research on improving material imperfections and controlling the coefficient of thermal expansion in the A2M3O12 family are systematically summarized. Finally, challenges and questions about the developments of these A2M3O12 NTE compounds in future studies are also discussed.

Argentophilicity induced anomalous thermal expansion behavior in a 2D silver squarate

A 2D bilayer coordination polymer has been found to exhibit colossal interlayer PTE and in-plane NTE owing to argentophilic interactions.