- Negative thermal expansion
Negative Thermal Expansion (NTE) is a physicochemical process in which some materials contract upon heating rather than expanding as most materials do. Materials which undergo this unusual process have a range of potential engineering, photonic, electronic, and structural applications. For example, if one were to mix a negative thermal expansion material with a "normal" material which expands on heating, it could be possible to make a zero expansion composite material, such as Invar.
Origin of Negative Thermal Expansion
There are a number of physical processes which may cause contraction with increasing temperature, including transverse vibrational modes, Rigid Unit Modes and phase transitions.
Recently, Liu et al.  showed that the NTE phenomenon originates from the existence of high pressure, small volume phases with higher entropy, with their configurations present in the stable phase matrix through thermal fluctuations.
There are many potential applications for materials with controlled thermal expansion properties, as thermal expansion causes many problems in engineering, and indeed in everyday life. One simple example of a thermal expansion problem is the tendency of dental fillings to expand by an amount different from the teeth, for example when drinking a hot drink, causing toothache. If dental fillings were made of a composite material containing a mixture of materials with positive and negative thermal expansion then the overall expansion could be precisely tailored to that of tooth enamel.
Glass-ceramic is used for cooktops.
Perhaps one of the most studied materials to exhibit negative thermal expansion is Cubic Zirconium Tungstate (ZrW2O8). This compound contracts continuously over a temperature range of 0.3 to 1050 K (at higher temperatures the material decomposes). Other materials that exhibit this behaviour include: other members of the AM2O8 family of materials (where A = Zr or Hf, M = Mo or W) and ZrV2O7. A2(MO4)3 also is an example of controllable negative thermal expansion.
Quartz and a number of zeolites also show NTE over certain temperature ranges. Fairly pure silicon has a negative coefficient of thermal expansion for temperatures between about 18 K and 120 K. Cubic Scandium trifluoride has this property which is explained by the quartic oscillation of the fluoride ions. The energy stored in the bending strain of the fluoride ion is proportional to the fourth power of the displacement angle, unlike most other materials where it is proportional to the square of the displacement. A fluorine atom is bound to two scandium atoms, and as temperature increases the fluorine oscillates more perpendicularly to its bonds. This draws the scandium atoms together throughout the material and it contracts. ScF3 exhibits this property from 10K to 1100K above which it shows the normal positive thermal expansion.
- ^ Liu, Zi-Kui; Wang, Yi; Shang, Shun-Li (2011). "Origin of negative thermal expansion phenomenon in solids". Scripta Materialia 65 (8): 664. doi:10.1016/j.scriptamat.2011.07.001.
- ^ Mary, T. A.; Evans, J. S. O.; Vogt, T.; Sleight, A. W. (1996). "Negative Thermal Expansion from 0.3 to 1050 Kelvin in ZrW2O8". Science 272 (5258): 90–92. Bibcode 1996Sci...272...90M. doi:10.1126/science.272.5258.90. http://www.sciencemag.org/cgi/content/abstract/272/5258/90.
- ^ Röttger, K.; Endriss, A.; Ihringer, J.; Doyle, S.; Kuhs, W. F. (1994). "Lattice constants and thermal expansion of H2O and D2O ice Ih between 10 and 265 K". Acta Crystallographica Section B Structural Science 50 (6): 644–648. doi:10.1107/S0108768194004933.
- ^ Lightfoot, Philip; Woodcock, David A.; Maple, Martin J.; Villaescusa, Luis A.; Wright, Paul A. (2001). "The widespread occurrence of negative thermal expansion in zeolites". Journal of Materials Chemistry 11: 212–216. doi:10.1039/b002950p.
- ^ Attfield, Martin P. (1998). "Strong negative thermal expansion in siliceous faujasite". Chemical Communications (5): 601–602. doi:10.1039/A707141H.
- ^ Bullis, W. Murray (1990). "Chapter 6". In O'Mara, William C.; Herring, Robert B.; Hunt, Lee P.. Handbook of semiconductor silicon technology. Park Ridge, New Jersey: Noyes Publications. p. 431. ISBN 0-8155-1237-6. http://books.google.com/?id=COcVgAtqeKkC&pg=PA431&dq=silicon+negative+%22coefficient+of+thermal+expansion%22#v=onepage&q=silicon%20negative%20%22coefficient%20of%20thermal%20expansion%22&f=false. Retrieved 2010 -07-11.
- ^ Woo, Marcus (7 November 2011). "An incredible shrinking material: Engineers reveal how scandium trifluoride contracts with heat". Physorg. http://www.physorg.com/news/2011-11-incredible-material-reveal-scandium-trifluoride.html. Retrieved 8 November 2011.
- ^ Greve, Benjamin K.; Kenneth L. Martin, Peter L. Lee, Peter J. Chupas, Karena W. Chapman, Angus P. Wilkinson (19 October 2010). "Pronounced negative thermal expansion from a simple structure: cubic ScF(3).". Journal of the American Chemical Society 132 (44): 15496–15498. doi:10.1021/ja106711v. PMID 20958035. http://pubs.acs.org/doi/abs/10.1021/ja106711v.
- Li, J.; Yokochi, A.; Amos, T. G.; Sleight, A. W. (2002). "Strong Negative Thermal Expansion along the O−Cu−O Linkage in CuScO2". Chemistry of Materials 14 (6): 2602. doi:10.1021/cm011633v.
- Noailles, L. D.; Peng, H.-h.; Starkovich, J.; Dunn, B. (2004). "Thermal Expansion and Phase Formation of ZrW2O8Aerogels". Chemistry of Materials 16 (7): 1252. doi:10.1021/cm034791q.
- Grzechnik, A.; Crichton, W. A.; Syassen, K.; Adler, P.; Mezouar, M. (2001). "A New Polymorph of ZrW2O8Synthesized at High Pressures and High Temperatures". Chemistry of Materials 13 (11): 4255. doi:10.1021/cm011126d.
- Sanson, A.; Rocca, F.; Dalba, G.; Fornasini, P.; Grisenti, R.; Dapiaggi, M.; Artioli, G. (2006). "Negative thermal expansion and local dynamics in Cu2O and Ag2O". Physical Review B 73 (21). Bibcode 2006PhRvB..73u4305S. doi:10.1103/PhysRevB.73.214305.
- Bhange, D. S.; Ramaswamy, Veda (2006). "Negative thermal expansion in silicalite-1 and zirconium silicalite-1 having MFI structure". Materials Research Bulletin 41 (7): 1392–1402. doi:10.1016/j.materresbull.2005.12.002.
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