displacive transition

A transition in which a displacement of one or more kinds of atoms or ions in a crystal structure changes the lengths and/or directions of bonds, without severing the primary bonds. Examples: The transitions of the low-temperature polymorphs of SiO2 (quartz, tridymite and cristobalite) to their respective high-temperature polymorphs, which involve distortions or rotations of the SiO4 tetrahedra. Also Jahn–Teller and ferroic transitions.
PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 581 (https://doi.org/10.1351/pac199466030577)