Thermoelectric Properties of the New Polytelluride Ba₃Cu_14-δTe₁₂

Abstract

Ba 3 Cu 14-δ Te 12 was prepared by directly reacting the elements in stoichiometric ratios at 800°C for 3 days, followed by slow cooling. Ba 3 Cu 14-δ Te 12 forms a new structure type, space group P2 1 /m, with lattice dimensions of a ) 11.909(2) Å, b ) 21.174(4) Å, c ) 11.983(2) Å, ) 117.071(4)°, and V ) 2690.6(8) Å 3 , for δ ) 0.35(2) (Z ) 4). The structure contains corner-, edge-, and face-sharing CuTe 4 tetrahedra interconnected with almost planar CuTe 3 units. These connections result in a three-dimensional Cu atom network with numerous Cu-Cu bonds. With two Te 2 2-dumbbells per formula unit, Ba 3 Cu 14-δ Te 12 is an electron-precise compound when δ ) 0, according to (Ba 2+ ) 3 (Cu + ) 14 (Te 2 2-) 2 (Te 2-) 8 . For δ > 0, the materials are degenerate semiconductors with moderate Seebeck coefficients and electrical conductivities, in accord with the electronic structure calculations, and exhibit extremely low thermal conductivity.

Synthesis, Structure, and Thermoelectric Properties of Barium Copper Polychalcogenides with Chalcogen‐Centered Cu Clusters and Te22– Dumbbells

“…For x Ͼ 0, Ba 3 Cu 14-x Te 12 was thus predicted to be a pdoped semiconductor, in agreement with the physical property measurements. [12] Using two different chalcogen atoms may lead to the formation of new structure types, as demonstrated recently with the structures of Ba 2 Cu 4-x Se y Te 5-y , [14] Ba 3 Cu 17-x Se yTe 11-y , [19] Ba 2 Cu 6-x STe 4 and Ba 2 Cu 6-x Se y Te 5-y , [20] and Ta 15 -Si 2 Se y Te 10-y . [21] Here we present the new, isostructural, electron-deficient Zintl phases BaCu 6-x Q 1-y Te 6+y with Q = S and Se, containing the above-mentioned Te 2 2-dumbbells.…”

“…Such bonds between d 10 elements are not uncommon, [27] and their bonding character is usually derived from the hybridization effect. [28][29][30] These Cu-Cu distances are comparable with those ranging from 2.62 to 2.73 Å in the polytellurides Ba 2 Cu 4-x Se yTe 5-y , [14] as well as in Ba 3 Cu 14-x Te 12 [12] and Ba 3 Cu 17-x Se yTe 11-y , [19] where the bonding character was confirmed by calculations of their crystal orbital Hamilton populations. [31,32] Thus, the S/Se atoms, in part with Te contribution depending on the Se/Te ratio, are centering metal clusters with metal-metal bonds in BaCu 6-x Q 1-y Te 6+y .…”

“…Correspondingly, the Ba-Te distance of 3.75 Å in BaCu 5.9 -SeTe 6 is larger than that in most Ba-Cu tellurides with a typical coordination number of nine and Ba-Te bonds in part shorter than 3.5 Å. [12,14] On the other hand, it is unusual that the Se site should be encapsulated in an Cu 8 cube in BaCu 5.9 SeTe 6 with formally eight Cu-Se bonds of 2.41 Å, even when considering that about 25 % of the Cu sites are unoccupied, that is, roughly 2 out of 8. Three symmetrically inequivalent SeCu 6 polyhedra are possible.…”

“…[5][6][7] This includes polysulfides in lithium-sulfur batteries [8] as well as polytellurides in thermoelectrics, for example HfTe 5 and Te 2 2-dumbbells, [9] and in pnp-junctions, such as the phase-change material Ag 10 Te 4 Br 3 . [10] In recent years, we have uncovered several new polychalcogenides by using barium and copper or silver as cations, including Ba 2 Ag 4 Se 5 with its linear Se 3 4-unit, [11] Ba 3 Cu 14-xTe 12 with Te 2 2-dumbbells, [12] Ba 6.76 Cu 2.42 Te 14 with Vshaped Te 3 2-units, [13] and most recently Ba 2 Cu 4-x Se y Te 5-y , a mixed selenide-telluride with linear Te atom chains. [14] In the latter case, two different structures exist, depending on whether Se is incorporated into the structure.…”

Silver(I)-(poly)chalcogenide Halides – Ion and Electron High Potentials

“…The high mobility of the coinage metals often helps to reduce the thermal conductivity below the values of commercially thermoelectrics as shown for Ba 3 Cu 14−δ Te 12 [34].…”