Transmission electron microscopy was used to study twin structures, in the monoclinic phase, in the as-cast state or after annealing at high temperatures. Selected-area electron diffraction patterns, which appeared to indicate orthorhombic symmetry, were explained as being due to repeated (001) micro-twins of the monoclinic phase. Structural models for (100)-(20¯1) 5-fold twins were proposed which were different to previously published ones.

X.L.Ma, H.Liebertz, U.Köster: Physica Status Solidi A, 1996, 158[2], 359-67