Cu_9.1Te₄Cl₃: A Thermoelectric Compound with Low Thermal and High Electrical Conductivity

Abstract

Cu9.1Te4Cl3 is a new polymorphic compound in the class of coinage metal polytelluride halides. Copper is highly mobile, which results in multiple order–disorder phase transitions in a limited temperature interval from 240 to 370 K. Mainly as a consequence of thermal transport properties, the compound’s thermoelectric figure of merit reaches values up to ZT = 0.15 in the temperature range between room temperature and 523 K. Its structure is closely related to that of Ag10Te4Br3, another coinage metal polytelluride halide, which represents the first p–n–p-switchable semiconductor approachable by a simple temperature change. The title compound outperforms Ag10Te4Br3 in terms of thermoelectric properties by 1 order of magnitude and therefore acts as a link between the class of p–n–p compounds and thermoelectric materials.

Ion Dynamics and Polymorphism in Cu20Te11Cl3

“…In Figure A, the anion substructure of α-Cu 20 Te 11 Cl 3 is denoted. The crystal structure of Cu 20 Te 11 Cl 3 exhibits similarities to those of the structurally related coinage metal polytelluride halides Ag 10 Te 4 Br 3 20 and Cu 9.1 Te 4 Cl 3 but also contains new structure features that have not been reported in this material class before. Similar to the other compounds in its class, Cu 20 Te 11 Cl 3 can be described topologically by anion networks.…”

“…Thermal analysis was performed for Cu 20 Te 11 Cl 3 in order to verify ion dynamics and to check the occurrence of polymorphism. Like the structurally related polytelluride halides Ag 10 Te 4 Br 3 and Cu 9.1 Te 4 Cl 3 , Cu 20 Te 11 Cl 3 is a polymorphic compound and shows several thermal effects in a narrow temperature range below the synthesis temperature. , As can be seen in Figure , the DSC analysis shows two endothermic effects at 298 and 450 K that are assigned the γ → β and β → α phase transitions. Full DSC data are shown in Figure S2.…”

“…Projections of the anionic substructures of α-Cu 20 Te 11 Cl 3 (A), α-Cu 9.1 Te 4 Cl 3 (C), and α- and γ-Ag 10 Te 4 Br 3 (D and B). , The parameter d nets equals 2 times the distance between two Te 6 3 nets and is marked in red. Light-blue dots represent the Te sites of the vertically interpenetrating strands for better differentiation.…”

“…Until now, other materials that have been discovered to show this p–n–p switching behavior are the chalcogenides AgBiSe 2 , AgCuS, and Tl 2 Ag 12 Se 7 . − In 4 Se 3– x shows related modulations of the Seebeck coefficient but no switch in the type of semiconduction. , For Ag 10 Te 4 Br 3 , substitutions of the chalcogenides (Te by S and Se) and the halides (Br by Cl and I) as well as the coinage metal (Ag by Cu) exist. Cu 9.1 Te 4 Cl 3 , the first coinage metal polychalcogenide halide with exclusively Cu as coinage metal, has previously been published . It outperforms Ag 10 Te 4 Br 3 in terms of the thermoelectric properties by 1 order of magnitude with a ZT of 0.15 at 250 °C.…”

Trendbericht Festkörperchemie

“…4. Ausschnitte der Kristallstrukturen von α-und β-Cu 9,1 Te 4 Cl 3 , welche die Unterschiede der kettenartig angeordneten Te 2 -Hanteln und die von Cu-Atomen besetzten Positionen verdeutlichen 11).…”