Structural phase transitions in crystals of D2d3symmetry

Publisher Website
Google Scholar
Abstract
Applying Landau's thermodynamical group theory (1937), the permitted symmetries of soft modes and the permitted symmetries of the low-temperature phase of crystals with the space group D2d3 undergoing structural phase transitions are determined. It is found that crystals of symmetry D2d3, as the result of a structural phase transition, can either undergo changes in symmetry within the tetragonal system (D2d to D2d,S4) or change their symmetry from tetragonal to rhombic (D2d to D2,C2v) or from tetragonal to monoclinic (D2d to C2,Cs). Ferrodistorsive transitions are possible in which the volume of the unit cell remains unchanged, and antiferrodistorsive transitions in which the unit cell doubles in size. The calculations do not take into account phenomena occurring in the critical region but deal only with the static properties of the crystals.