Cornucopia of Structures in the Pseudobinary System (SnSe)_xBi₂Se₃: A Crystal-Chemical Copycat

Abstract

Pseudobinary phases (SnSe) BiSe exhibit a very diverse structural chemistry characterized by different building blocks, all of which are cutouts of the NaCl type. For SnSe contents between x = 5 and x = 0.5, several new phases were discovered. Next to, for example, SnBiSe ( x = 4) in the NaCl structure type and SnBiSe ( x = 0.5) in the layered defect GeSbTe structure type, there are at least four compounds (0.8 ≤ x ≤ 3) with lillianite-like structures built up from distorted NaCl-type slabs (L4,4-type SnBiSe, L4,5-type SnBiSe, L4,7-type SnBiSe, and L7,7-type SnBiSe). For two of them (L4,7 and L7,7), the cation distributions were determined by resonant X-ray scattering, which also confirmed the presence of significant amounts of cation vacancies. Thermoelectric figures of merit ZT range from 0.04 for SnBiSe to 0.2 for layered SnBiSe; this is similar to that of the related compounds SnBiTe or PbBiTe. Compounds of the lillianite series exhibit rather low thermal conductivities (∼0.75 W/mK for maximal ZT). More than other "sulfosalts", compounds in the pseudobinary system SnSe-BiSe adapt to changes in the cation-anion ratio by copying structure types of compounds containing lighter or heavier homologues of Sn, Bi, or Se and can incorporate significant amounts of vacancies. Thus, (SnSe) BiSe is a multipurpose model system with vast possibilities for substitutional and structural modification aiming at the optimization of thermoelectric or other properties.

Effective Mass Enhancement and Thermal Conductivity Reduction for Improving the Thermoelectric Properties of Pseudo‐Binary Ge2Sb2Te5

“…Some layered pseudo-binary compounds consisting of IV-VI and V 2 -VI 3 families may also have outstanding thermoelectric performances. So far, (SnSe)(Bi 2 Se 3 ) 2 , [17] (ATe)(Bi 2 Te 3 )(A = Ge, Sn, Pb), [18] (ATe)(Sb 2 Te 3 )(A = Ge, Sn), [19] (GeTe) 3 (Sb 2 Te 3 ) [20] have been gradually explored as promising thermoelectric materials. Ge 2 Sb 2 Te 5 is one of the most famous phase-change materials used in data storage and reading.…”

A Layered Tin Bismuth Selenide with Three Different Building Blocks that Account for an Extremely Large Lattice Parameter of 283 Å

“…In the pseudobinary system (SnSe) x Bi 2 Se 3 , compounds with very diverse structures are formed . Besides cubic Sn 4 Bi 2 Se 7 ( x= 4) with defect NaCl‐type structure, and layered SnBi 4 Se 7 ( x= 0.5) with defect GeSb 2 Te 4 ‐type structure, at least four compounds (0.8≤ x ≤3) with structures derived from lillianite (Pb 3 Bi 2 S 6 ) have been discovered.…”

“…A complex layered phase with the chemical composition Sn 2.8(4) Bi 20.2(4) Se 27 was formed during the decomposition of samples of SnBi 4 Se 7 with defect GeSb 2 Te 4 ‐type structure . The fact that this decomposition occurred during repeated slow heating indicates that the new phase is most likely thermodynamically stable at temperatures below ≈500 °C.…”

“…The heterogeneous product was examined by scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDX), which revealed regions of different contrast and composition (Figure S1 and Table S1, “S” denotes Figures and Tables in the Supporting Information). In addition to a minority phase, which according to EDX corresponds to Sn 11.49 Bi 12.39 Se 30 , and a main phase of Sn 0.85 Bi 2.15 Se 4 , the title compound has been identified as a main component that is slightly Sn‐depleted compared to the nominal composition SnBi 4 Se 7 .…”

“…Sn 2.8(4) Bi 20.2(4) Se 27 was formed during the decomposition of a quenched sample of SnBi 4 Te 7 upon repeated heating. For TEM measurements, the powdered sample was drop‐cast on a copper grid coated with a holey carbon film.…”