A transition in which the space-group symmetry of the lower symmetry phase is a subgroup
of that of the higher symmetry phase. Example: The transition of the low-temperature
polymorph of quartz characterized by space-group symmetry
(trigonal), to the high temperature polymorph of quartz with space-group symmetry,
(hexagonal). Synonymous with symmetry-breaking transition
(note: this term, strictly speaking, is no longer in use).
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations
on page 591
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. https://doi.org/10.1351/goldbook