Structural phase transition in crystals with Fm3m symmetry

A systematic study of the possible phase symmetries derived from a prototype phase with the space group Fm3m (O h 5 ) has been performed. These structural phase transitions involve the onset of an order parameter transforming according to one irreducible representation of the prototype space group. The investigation is performed on the basis of the Landau theory for continuous transitions. Accordingly, the irreducible representations of Fm3m are examined at the Gamma ,X,L and W high-symmetry points of the cubic face-centered Brillouin zone. The order parameters relevant to all the arms of a given star are considered. The results are summarised in several tables. These results are discussed and compared with the available experimental data relative to Fm3m subgroups.