The corresponding fast Fourier transform (FFT) image is shown in the inset. Similar structural transformations were previously observed in carbon (diamond → lonsdaleite) and in silicon (SiI → SiIV) . According to , the lattice parameters of wurtzite BP are а = 0.320 nm and с = 0.531 nm, which are noticeably different from the lattice parameters of wurtzite BN (а = 0.25505 nm; с = 0.4210 nm ). As follows from the comparison of FFT images of two neighboring fragments (see insets in Fig. ), the (-111) 3C ǁ (001) 3R orientation relation is observed. According to our assessment, the lattice parameters of the rhombohedral phase are a = 0.321 nm, c = 0.786 nm.