A transition in which the molar Gibbs energies or molar Helmholtz energies of the
two phases (or chemical potentials of all components in the two phases) are equal
at the transition temperature, but their first derivatives with respect to temperature
and pressure (for example, specific
enthalpy of transition and
specific volume) are discontinuous at the transition point, as for two dissimilar phases that coexist
and that can be transformed into one another by a change in a field
variable such as pressure, temperature, magnetic or electric field. Example: The transition
on heating
CsCl
to
at which it changes from the low-temperature,
CsCl-type structure to the high-temperature
NaCl-type structure. Synonymous with discontinuous phase transition.
Source:
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations
1994))
on page 583