Substances showing negative thermal expansion (NTE) over small temperature ranges have long been known. For example, water exhibits negative thermal expansion over a range of several degrees close to its freezing point. The world we live in would be a very different place if it were not for that NTE, which causes ice to float on water. NTE is also known to occur in many materials, such as silicon (Si), at very low temperatures, but this NTE disappears well before approaching ambient temperature. NTE also occurs well above ambient temperature over limited temperature ranges in materials such as some crystalline forms of silicon dioxide (SiO₂). The discovery in 1995 that cubic zirconium tungstate (ZrW₂O₈) exhibits strong NTE over a temperature range exceeding 1000°C led to a surge of interest in materials exhibiting NTE.