Tl₂AXTe₄ (A = Cd, Hg, Mn; X = Ge, Sn):  Crystal Structure, Electronic Structure, and Thermoelectric Properties

Abstract

The six new compounds Tl 2 CdGeTe 4 , Tl 2 CdSnTe 4 , Tl 2 HgGeTe 4 , Tl 2 HgSnTe 4 , Tl 2 MnGeTe 4 , and Tl 2 -MnSnTe 4 have been synthesized. All six compounds are isostructural and crystallize in the tetragonal space group I-42m with a ≈ 8.3 Å and c ≈ 7.1 Å. The structure is composed of chains of composition [AXTe 4 ] 2separated by Tl 1+ ions, an ordered superstructure of the TlSe structure type. In addition to their syntheses and crystal structures, we report the calculated electronic structures of these six compounds and of the related compounds KInTe 2 and TlInTe 2 . We measured the thermoelectric properties (electrical resistivity, thermopower, and thermal conductivity) of Tl 2 CdGeTe 4 , Tl 2 CdSnTe 4 , Tl 2 HgGeTe 4 , and Tl 2 -HgSnTe 4 . These compounds are semiconductors with very low thermal conductivities and moderately high thermopowers. However, as currently prepared they have resistivities that are too high for thermoelectric applications. Magnetic susceptibility and resistivity measurements show Tl 2 MnGeTe 4 and Tl 2 MnSnTe 4 to be Mott insulators, in agreement with spin-polarized band structure calculations.

Supercubooctahedron (Cs6Cl)2Cs5[Ga15Ge9Se48] Exhibiting Both Cation and Anion Exchange

“…Considering the excellent thermal stabilityo f 1 (stable up to 950 Ka ccording to the thermogravimetric data; see the Supporting Information, Figure S6), as eries of solidstate flux ion-exchange experiments were designed and successfully carriedo ut ( Figure 3, Supporting Information). The thermals tability of 1 is about 400 8Ch igher than those of conventional supertetrahedral clusters containing organic templates, such as (C 7 H 10 N) 2 [Ga 10 S 16 (NC 7 H 9 ) 4 ]( 573 K) [26] and ZBT-1( 527 K). [21] For at ypical ion-exchange reaction shown in Figure 3, hand-picked single crystals of 1 (25 mg) were mixed with CsBr (100 mg) and KBr (37.3 mg) fluxes in as ealed silica tube under vacuum, heated to 923 Kf ollowed by ad well time of 60 h, and then cooled to 473 K( see the Supporting Information).…”

“…[21] For at ypical ion-exchange reaction shown in Figure 3, hand-picked single crystals of 1 (25 mg) were mixed with CsBr (100 mg) and KBr (37.3 mg) fluxes in as ealed silica tube under vacuum, heated to 923 Kf ollowed by ad well time of 60 h, and then cooled to 473 K( see the Supporting Information). About 15 mg of clearl ight yellow crystals of (Cs 6 Br) 2 and cation-exchanged product (Rb 6 Br) 2 Cs 5 [Ga 15 Ge 9 Se 48 ]( 6 )a s orange-yellow crystals ( Figure 3; see the Supporting Information, Ta bles S1 and S2).…”

“…25 mg) were sealed in silica tubes under vacuum and then heated at ar ate of 15 Kh À1 to 923 K, followed by ad well time of 60 h, and subsequently cooled at ar ate of 5.4 Kh À1 to 473 K, before switching off the furnace. After washing with distilled water and ethanol to remove the flux, the clear,l ight yellow crystals of (Cs 6 Br) 2 Ge 9 Se 48 ]( 3 )w as obtained by using CsI (100 mg) and KI (42.6 mg) as mixed fluxes with am olar ratio of 6:4( m.p. 809 K) [28] together with single crystals of 1 (ca.…”

“…[1][2][3] Among them, large chalcogenide clusters are remarkable not only because of their beautiful structuralc hemistry of precisely defined size and composition, but also their properties, such as photocatalysis [4] and photoluminescence. [5] Intrinsically,t hese properties are associated with the secondary buildingu nits (SBUs), nanosized supertetrahedral clusters constructed from the primary buildingu nits, MQ 4 tetrahedra (M = metal, Q = chalcogen), through sharing apexes or edges.…”

“…Herein, we report an ovel type of supertetrahedral connectivity in the supercubooctahedron of (Cs 6 Cl) 2 Cs 5 [Ga 15 Ge 9 Se 48 ] (1), the largestc halcogenide cluster containing only period 4 elements. The supercubooctahedron is constructed from 72 skeleton atoms originating from eight M 3 Se 9 SBUs (M = disordered Ga/Ge;F igure 1).…”