dilational transition (dilatational transition)

https://doi.org/10.1351/goldbook.D01733
A transition in which the crystal structure is dilated (or compressed) along one (or more) crystallographic direction(s) while the symmetry about that direction is retained. Examples:
  1. The transition of a CsCl-type structure to a rock @[email protected] structure in which dilation occurs along the three-fold axis.
  2. The transition at \(T_{\text{D}}\) in quenched NiS in which volume expansion occurs without change of symmetry on going from a metallic state (\(T > T_{\text{D}}\)) to a semiconducting state (\(T < T_{\text{D}}\)).
Source:
PAC, 1994, 66, 577. (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 581 [Terms] [Paper]