According to TEM data, both B 6 S and B 6 Se powders consist of flat polyhedral particles with dimensions ranging from 20 to several hundred nanometers (Fig. ), a significant proportion of which contain twins with coherent twin boundaries. Fig. shows a fragment of the B 6 S structure with ABAB stacking. In contrast to Fig. , where such a structure was formed during twinning as a result of the appearance of individual stacking faults, here the ABAB stacking is not presented fragmentarily, but throughout the entire section. As we can see, the ABAB structure is formed in two ways: as a layer within the initial phase with ABCDABCD stacking as a result of the appearance of the stacking fault, or it can be formed as an independent structure in a large fragment of the particle. Fig. shows a deformation band in B 6 S along the plane (011) (indicated by the arrow). Similar deformation bands are found in many materials after various types of deformation. Phase transformations, recrystallization, and transitions from a crystalline state to a disordered and/or amorphous state can occur in the deformation (or shear) bands. Shear bands are widely observed in all types of materials: metals, polycrystalline alloys, metallic glasses, rocks, ceramics, organic compounds, polymers and fullerenes. The band in Fig. shows amorphous fragments formed as a result of disorder in the crystalline lattice. Shear bands represent regions where inelastic shear deformation is significantly localized and exceeds the deformation in the surrounding material. They represent a mode of nonelastic response of the material to mechanical stress . Similar shear bands were previously observed in B 4 C , whose crystal lattice is formed by distorted B 11 C icosahedra connected by C-B-C three-atom chains. As in the present work, the cracks and amorphous bands in B 4 C are located along the same plane. The formation of amorphous bands during shear deformation has been explained as a result of the fracture of icosahedra . The formation of cracks is evidence of cleavage, a property of a crystal to split along certain crystallographic directions due to the structural peculiarities of its crystal lattice. The cleavage planes and the crystal planes characterized by the highest density of atoms usually coincide. The direction of crack propagation is assumed to be almost strictly perpendicular to the direction of load application. Crack propagation occurs by successive and recurrent breaking of atomic bonds along specific crystallographic planes. As can be seen from the corresponding FFT images, all the cracks are in the {011} planes, and while in B 6 S there are many cracks and they all correspond to (011) planes, in B 6 Se there are cracks that belong to both (011) and (0-11) planes. Thus, both shear bands and cracks present in B 6 S and B 6 Se lie in {011} planes. Fig. shows the twinning structure in B 6 Se. The twinning plane is the same as in B 6 S, i.e. (101).