The influence of the substitution in cation and anion sublattice on the HT-Pb₂GeS₄ structure

Abstract: The HT- Pb₂GeS₄ (SG I-43d) is a prospective material for investigation. The structure of HT- Pb₂GeS₄ crystallizes in cubic symmetry. The positions 24d, 16c, and 48e can be modified through the substitution of atoms Pb and S. We investigated the crystalline structure of four compositions, Pb_1.9Sn_0.1GeS_3.52Se_0.48, Pb_1.86Sn_0.14GeS_3.32Se_0.68, Pb_1.82Sn_0.18GeS_3.16Se_0.84, and Pb_1.58Sn_0.42GeS_3.64Se_0.36, changing the cation and anion sublattice simultaneously.

Samples with the nominal compositions of Pb_2-xSn_xGeS_4-ySe_y (x = 0.1, 0.14, 0.18, and 0.42; y = 0.36, 0.48, 0.68, and 0.84) were prepared by melting high-purity Pb (shot, 99.99 %), Sn (shot, 99.99 %), Ge (shot, 99.999 %), S (shot, 99.99 %), and Se (shot, 99.99 %) in quartz containers evacuated to a residual pressure of 10^–2 Pa. The total mass of every sample was 1 g. The ampules with the stoichiometric mixtures of elements were heated up to 1423 K at a rate of 12 K/h; kept at this temperature for 4 h; cooled down to 773 K at a rate of 12 K/h; annealed at this temperature for 500 h; and quenched in cold water without breaking the containers.

The substitution in cation and anion sublattice on the Pb₂GeS₄ crystal structure leads to the increase in the volume of the lattice from 2794.9 Å to 2852.2 Å due to the change of y. The lattice parameter a changes from 14.086 Å to 14.1816 Å. A distortion of the cation sublattice is also observed.

Hence, such peculiarities of the crystal structure may improve some thermoelectric and optical properties.