The phase equilibria along the Bi₁₉S₂₇I₃ -“Bi₁₉Se₂₇I₃” section of the Bi₂S₃– Bi₂Se₃ -BiI₃ system have been investigated based on a comparative analysis of DTA measurements, PXRD patterns, and SEM results. It has been established that the system is partially stable in the subsolidus area and forms a wide series of solid solutions (δ -phase) with a hexagonal structure based on . The solubility limit based on Bi₁₉S₂₇I₃ in this section at room temperature is ~70 mol%. The crystal lattice parameters change linearly within the homogeneity area, in accordance with Vegard's law. Compositions less enriched in  consist of heterogeneous mixtures, including δ-solid solutions based on  and . The obtained materials are of interest as potential candidates for thermoelectric and photoelectric applications.

doi.org/10.32737/0005-2531-2026-2-145-152