This monoclinic phase exhibited a tendency to form multiple twins with 5-fold symmetry, and a transmission electron microscopic study was made of the associated mechanisms. In addition to the well-known (001) and (100) glide twins, (20-1) glide twins were also found. Alternating (100)-(20-1) or (100)-(001)-(100) twinning was also expected to yield twins which exhibited 5-fold symmetry. The distribution of Co atoms in the pentagonal layer, and the tessellation of pentagons in the (100) and (20-1) glide twins, was also studied by means of high-resolution electron microscopy.

X.L.Ma, K.H.Kuo: Metallurgical and Materials Transactions A, 1995, 26[4], 757-63