A new material made of ytterbium, gallium and germanium has almost zero thermal-expansion coefficient, and, unlike similar substances, conducts electricity.
James Salvador of Michigan State University and colleagues have shown that this intermetallic compound remains the same size between 100 and 400 K. It could have many engineering applications, where high electrical or thermal conductivity is needed in addition to low thermal expansion.
The mechanism is not fully understood, but it seems to be electronic. Electrons move from ytterbium to gallium atoms, making the former shrink while the latter are much the same size. This shrinking just offsets the usual thermal expansion, so the material stays the same size as the temperature changes.
Further reading
James R Salvador et al. 2003 Nature 425 702.