transition temperature

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In crystallography, the transition temperature is the temperature at which a material changes from one crystal state (allotrope) to another.{{Cite book |last=Daintith |first=John |title=A Dictionary of Chemistry |publisher=Oxford University Press |year=2008 |isbn=9780199204632 |edition=6th |language=en |chapter=allotropy |url=https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095404490 }} More formally, it is the temperature at which two crystalline forms of a substance can co-exist in equilibrium. For example, when rhombic sulfur is heated above 95.6 °C, it changes form into monoclinic sulfur; when cooled

below 95.6 °C, it reverts to rhombic sulfur. At 95.6 °C the two forms can co-exist. Another example is tin, which transitions from a cubic crystal below 13.2 °C to a tetragonal crystal above that temperature.

In the case of ferroelectric or ferromagnetic crystals, a transition temperature may be known as the Curie temperature.