Two Mixed-Anion Semiconductors in the Ba–Sn–Te–S System with Low Thermal Conductivity

Abstract

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.

A unique [Sb6O2S13]12−finite chain in oxychalcogenide Ba6Sb6O2S13leading to ultra-low thermal conductivity and giant birefringence

“…22 Moreover, the calculated minimum lattice thermal conductivity ( κ min ) of Ba 6 Sb 6 O 2 S 13 was estimated using Cahill's model at about 0.27 W m −1 K −1 . 23 The reason for Ba 6 Sb 6 O 2 S 13 possessing an ultra-low κ L value can be mainly attributed to the following two aspects: (i) strongly ionic Ba 2+ cations can decrease the phonon velocity and boost the phonon scattering ratio, and similar examples can also be found in other Ba-based systems; 24 (ii) due to the coexistence of multiple BBUs, the highly polarized [SbOS 2 ] triangular pyramid, [SbOS 3 ], and the [SbS 4 ] square pyramid can effectively enhance the lattice anharmonicity. 25 Therefore, the low κ L value for Ba 6 Sb 6 O 2 S 13 was verified through experimental measurement and theoretical estimation.…”

Crystal structure, phase width, and physical properties of the barium tetrel selenides Ba6Si2−xGexSe12 (x = 0, 0.5, 1, and 1.5) with ultralow thermal conductivity

“…31 The compound Ba 6 Ge 2 Se 12 , which also features disorded Se 2 2− pairs, was recently reported to have a similarly low thermal conductivity of 0.33 W m −1 K −1 at 573 K, which may in part be attributed to its larger average molar mass and stronger Umklapp scattering due to its greater unit cell volume. 11 Barium tin chalcogenides that possess S/Te mixing such as Ba 5 Sn 2 S 7.673 Te 1.327 and Ba 7 Sn 3 S 12.161 Te 0.839 have demonstrated extremely low lattice thermal conductivity ranging from 0.3 to 0.4 W m −1 K −1 between 300 and 773 K. 32 Ultra-low thermal conductivity in thermoelectric selenides have been observed in K 2 Bi 8 Se 13 , which achieved thermal conductivity between 0.42 and 0.20 W m −1 K −1 from 300 to 873 K due to anisotropic K/Bi mixed sites. 33 Similarly, low thermal conductivity has been observed in the Bi 2+2n O 2+2n Se n X 2 (X = Cl, Br) family of layered selenides, which are composed of Bi 2 O 2 X 2 and Bi 2 O 2 Se layers that efficiently scatter phonon modes in the transverse and longitudinal directions.…”

Comparative Analysis of the Crystal Structures and Physical Properties of the Complex Group 14 Selenides Sr8Ge4Se17 and Ba8Sn4Se17

“…Exploratory research into alkaline earth chalcogenides has successfully resulted in the discovery of several compounds for applications in nonlinear optics, − thermoelectrics, − and photovoltaics. − Herein, we compare the crystal structures and physical properties of two new alkaline earth selenides with the same elemental ratios. While exploring the Ae–Tt–Q phase space (Ae = alkaline earth metal; Tt = tetrel, Q = chalcogenide), Sr 8 Ge 4 Se 17 and Ba 8 Sn 4 Se 17 were discovered.…”