New Materials, Compounds and Applications

This work reports the synthesis and structural characterization of Ge_2-xSn_xBi₂Te₅ (0 ≤ x ≤ 2) solid solutions with tetradymite-related architecture. Polycrystalline samples were prepared from presynthesized GeTe, SnTe and Bi₂Te₃ via melting at 750 °C, rapid quenching and prolonged annealing at 500 °C to approach equilibrium. Phase constitution and crystal structure were examined by powder X-ray diffraction (XRD), supported scanning electron microscopy (SEM). The XRD patterns of the investigated compositions show reflections attributable to the tetradymite-related layered phase, with no additional crystalline phases detected within the resolution of the method. With increasing Sn content, diffraction peaks shift systematically to lower angles, evidencing lattice expansion due to Ge/Sn substitution. Unit-cell parameters were determined by Le Bail profile fitting in the trigonal P-3m1 space group (hexagonal setting). Both a and c increase smoothly with x and the unit-cell volume follows a near-linear (Vegard-like) trend, consistent with a continuous substitutional solid solution and the absence of detectable structural transformation. SEM observations show dense microstructures without obvious secondary-phase contrast at the micrometer scale, in agreement with the diffraction results.