YbGaGe

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| OtherNames = Ytterbium Gallium Germanium

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| CrystalStruct = MoC₂ structure type

| SpaceGroup = P6₃/mmc (No. 194)

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| LattConst_a = 420.56 pm

| LattConst_c = 1678.1 pm

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YbGaGe is an alloy of ytterbium, gallium and germanium. It sparked interest because one group of researchers reported that it exhibits zero thermal expansion, while being conductive.{{Cite journal |doi = 10.1038/nature02011|pmid = 14562099|title = Zero thermal expansion in YbGa Ge due to an electronic valence transition|journal = Nature|volume = 425|issue = 6959|pages = 702–705|year = 2003|last1 = Salvador|first1 = James R|last2 = Guo|first2 = Fu|last3 = Hogan|first3 = Tim|last4 = Kanatzidis|first4 = Mercouri G| bibcode=2003Natur.425..702S |s2cid = 4412282}} Such materials have applications in space and other environments where low thermal expansion materials are required.{{cite web | url=http://pubs.acs.org/cen/NCW/8142notw1.html | title=Zero Expansion Conductor | date=October 20, 2003 | access-date=May 23, 2011 | pages=1}} However, subsequent measurements by other groups were not able to reproduce those results, but rather found expansion coefficients similar to copper.{{Cite arXiv |eprint = cond-mat/0407683|last1 = Janssen|first1 = Y|title = YbGaGe: Normal thermal expansion|last2 = Chang|first2 = S|last3 = Cho|first3 = B. K|last4 = Llobet|first4 = A|last5 = Dennis|first5 = K. W|last6 = McCallum|first6 = R. W|last7 = Mc Queeney|first7 = R. J|last8 = Canfield|first8 = P. C|year = 2004}}

Nevertheless, YbGaGe does show anomalous thermal expansion. Near-zero thermal expansion was observed by Booth et al. It was found that near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration. However, the near-zero thermal expansion mechanism remains elusive.{{Cite journal |doi = 10.1103/PhysRevB.75.012301|title = Ytterbium divalency and lattice disorder in near-zero thermal expansion YbGaGe|journal = Physical Review B|volume = 75|year = 2007|last1 = Booth|first1 = C. H|last2 = Christianson|first2 = A. D|last3 = Lawrence|first3 = J. M|last4 = Pham|first4 = L. D|last5 = Lashley|first5 = J. C|last6 = Drymiotis|first6 = F. R| issue=1 | page=012301 |arxiv = cond-mat/0611166| bibcode=2007PhRvB..75a2301B |s2cid = 94678137}}