Funct. Mater. 2022; 29 (3): 359-363.

The discovery of topological crystalline insulators (TCIs) with a metallic 2layer on the surface of a band-gap crystal and the prospects of their application in spintronics and quantum computation stimulate studies of the mechanisms of the transition to the TCI state. The semiconductor Pb_1-xSn_xTe solid solutions in the composition range corresponding to the inverted band structure were among the first discovered TCIs. One can suggest that due a strong electron-phonon interaction characteristic of these materials, the formation of a TCI layer is accompanied by some change in the properties determined by the lattice subsystem of the crystal. We measured the dependences of the lattice thermal conductivity λ_L of Pb_1-xSn_xTe on x in the vicinity of the TCI transition at different temperatures (170-300 K). In the λ_L(x) isotherms, we observed two peaks near x = 0.61 and x = 0.63, which evidences that the TCI transition consists of at least two stages. We suggest that one peak corresponds to the band inversion point and the other is associated with a structural self-organization taking place in the crystal, and either stimulates or accompanies the TCI transition. Thus, the transition to the TCI state in Pb_1-xSn_xTe is accompanied by changes in the lattice subsystem of the crystal.