https://doi.org/10.1351/goldbook.A00545

An equation, describing crystallization kinetics, of the form: \[1 - \varphi _{c} = \text{e}^{K\ t^{n}}\] where φ c is the crystalline volume fraction developed at time t and constant temperature, K and n are suitable parameters. K is temperature dependent. According to the original theory, n should be an integer from 1 to 4, the value of which should depend only on the type of the statistical model; however, it has become customary to regard it as an adjustable parameter that may be non-integral.*Source: *

Purple Book, 1^{st} ed., p. 85 (http://old.iupac.org/publications/books/author/metanomski.html)

Purple Book, 1