Abstract
While most solids expand when heated, some materials show the opposite behavior: negative thermal expansion (NTE). In polymers and biomolecules, NTE originates from the entropic elasticity of an ideal, freely jointed chain. The origin of NTE in solids has been widely believed to be different. Our neutron scattering study of a simple cubic NTE material, ScF3, overturns this consensus. We observe that the correlation in the positions of the neighboring fluorine atoms rapidly fades on warming, indicating an uncorrelated thermal motion constrained by the rigid Sc-F bonds. This leads us to a quantitative theory of NTE in terms of entropic elasticity of a floppy network crystal, which is in remarkable agreement with experimental results. We thus reveal the formidable universality of the NTE phenomenon in soft and hard matter.
| Original language | English |
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| Article number | eaay2748 |
| Journal | Science Advances |
| Volume | 5 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 1 2019 |
Funding
We gratefully acknowledge discussions with C. Li, A. Abanov, and P. Allen. D.W. thanks the Condensed Matter Physics and Materials Science Division at Brookhaven National Laboratory, where part of this work was performed during his summer internship, for the hospitality. Work at Brookhaven National Laboratory (BNL) was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy, under contract no. DE-SC0012704. Work at BNL’s Center for Functional Nanomaterials (CFN) is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under the same contract. This research at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.