A
second-order or
higher-order transition,
in which the
heat capacity shows either a discontinuity (second-order) or a vertex (higher-order) at the transition temperature. Example: The transition at

,
accompanied by a finite change in
specific heat capacity at constant pressure

,
of the low-temperature polymorph of quartz to the high-temperature polymorph.
Source:
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994))
on page 584
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
doi:10.1351/goldbook.