Compounds That Contract on Heating

Various mechanisms to explain negative thermal expansion in oxides are presented. Our search for compounds having this unusual property has focused on the mechanism based on transverse thermal motion of oxygen in M−O−M linkages. Such a mechanism can give strong negative thermal expansion over broad temperature ranges. Examples of compounds where this mechanism operates to give negative thermal expansion are ZrW2O8, the Sc2W3O12 family, NbOPO4, AlPO4-17, and faujasite SiO2.