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.^[1] Such materials have applications in space and other environments where low thermal expansion materials are required.^[2] However, subsequent measurements by other groups were not able to reproduce those results, but rather found expansion coefficients similar to copper.^[3]

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 NZTE mechanism remains elusive ^[4]