We synthesized two mixed-anion tin chalcogenides, Ba5Sn2Te1.327S7.673 (1) and Ba7Sn3Te0.839S12.161 (2), by a typical high-temperature solid-state reaction
using an evacuated silica tube for the first time in the system of
Ba–Sn–Q (Q = S1–x
Te
x
; 0 ≤ x ≤
1). Compound 1 crystallizes in the monoclinic space group P21/c with unit cell parameters
of a = 17.501(5) Å, b = 8.908(2)
Å, c = 12.508(3) Å, and Z = 4. Compound 2 has an orthorhombic space group Pnma with a = 12.386(5) Å, b = 24.17(2) Å, c = 8.872(4) Å,
and Z = 4. The structures of compounds 1 and 2 are both zero-dimensional (0D), and the formulas
can be written as Ba5(SnIVQ4)2Q and Ba7(SnIVQ4)3Q with Sn/Q ratios of 2/9 and 3/13, respectively. Compounds 1 and 2 exhibit Q2– anion units,
which is unique among Ba–Sn−Q compounds due to the [SnQ4] tetrahedra and low Sn/Q ratios. The phonon transport can be significantly
scattered because the weakly bond Ba atom and highly distorted [SnQ4] tetrahedra can enhance the lattice anharmonicity. As a result,
compounds 1 and 2 have low lattice thermal
conductivity (κlat) values of ∼0.3–0.4
W m–1 K–1 in the range of 300
to 773 K, which results in a design strategy as thermoelectric materials.