Phase transitions in solids of diperiodic symmetry.

All isotropy subgroups (and thus all quasicontinuous symmetry changes) corresponding to k points of symmetry have been obtained for the 80 diperiodic space groups. The detailed information for such phase transitions is given here for the diperiodic space group I'———.Only two distinct images (sets of representation matrices) occur for this example yielding Landau-Ginzburg-Wilson (LGW) Hamiltonians corresponding to the Ising and XY models, respectively. Minimization of the LGW Hamiltonians yields those transitions which are continuous in the mean-field description.