How to quantify isotropic negative thermal expansion: magnitude, range, or both?

Abstract

Negative thermal expansion (NTE) is the counterintuitive material property of volume contraction on heating. We compare different systems with contrasting mechanisms for isotropic NTE using the metric of NTE capacity.

A positive to negative uniaxial thermal expansion crossover in an organic benzothienobenzothiophene structure

“…As was outlined by Coates & Goodwin (2019) several mechanisms can be distinguished that may be responsible for volumetric and/or axial negative thermal expansion (NTE). Phonon-mediated NTE as found in open structures with directional covalent bonding favors a maximal temperature range in which the NTE occurs, although the NTE is not necessarily very strong.…”

Assessing negative thermal expansion in mesoporous metal–organic frameworks by molecular simulation

“…However, there was a noticeable change in contraction rate observed at approximately 300 K for DUT-49, which is discussed in Section 3.3. Given that NTE in MOF materials is considered a phononmediated phenomenon 35 it is unsurprising that NTE persists over this entire temperature range. Notably, this has also been experimentally observed for MOF-5, which shows NTE from 80-500 K. 36 The associated volumetric thermal expansion coefficients were also calculated over the entire temperature range, presented in Table 2, which provides a comparable metric for these materials.…”

Negative Thermal Expansion Design Strategies in a Diverse Series of Metal–Organic Frameworks

“…[1] While PTE is the norm in most materials, negative thermal expansion (NTE) has been observed in materials that include oxides, fluorides, cyanides, polymers, and carbon nanotubes. [2][3][4][5][6] A seminal discovery in this field was that ZrW 2 O 8 [7] exhibits isotropic NTE ( l = (1/l)dl/dT  -9 ppm K -1 ) over the 0.3 to 1050 K temperature range. [8] Since this finding, a number of experimental and theoretical studies have shed light on the vibrational modes leading to this behavior and their implications for the design of further NTE materials.…”