Minimal supergroups and magnetic space groups (III)

The Opechowski-Guccione (O. G.) symbols of magnetic space groups can be uniquely derived from the Belov (B.) symbols. The correspondance of B. to O. G. symbols provides at the same time the correspondance of a space group H to the supergroup G = H + g. H, g being a translation added to H, H being related to the B. symbol and G to the O. G. symbol. Results are tabulated for the crystal class mmm and indications are given for other classes. Examples illustrate how to find the general positions of G when those of H are known. Phase transitions from H to G are high temperature transitions accompanied by extinction rules which are specified