Synthesis and Structural and Physical Properties of New Semiconducting Quaternary Tellurides: Ba₄Ag_3.95Ge₂Te₉and Ba₄Cu_3.71Ge₂Te₉

Abstract

Two quaternary tellurides, Ba(4)Ag(3.95)Ge(2)Te(9) and Ba(4)Cu(3.71)Ge(2)Te(9), were prepared in evacuated silica tubes at 750 degrees C. Both tellurides crystallize in space group Pbam, with lattice parameters of a = 8.6835(3) A, b = 13.6421(4) A, c = 10.2612(3) A, and V = 1215.55(7) A(3) (Z = 2) for Ba(4)Ag(3.95)Ge(2)Te(9) and a = 8.6464(2) A, b = 13.5305(4) A, c = 10.0810(3) A, and V = 1179.38(6) A(3) (Z = 2) for Ba(4)Cu(3.71)Ge(2)Te(9). These structures are comprised of planar Ag(4)/Cu(4) clusters and dimeric Ge(2)Te(6) units, which are interconnected through Te atoms into a three-dimensional structure. Several split sites in the case of Ba(4)Cu(3.71)Ge(2)Te(9) are reflected in additional, different clusters, including a linear Cu(3) unit. The covalent Ag-Te/Ge-Te network surrounds a one-dimensional linear channel running along the c direction, encompassing the Ba atoms. Electronic structure calculations and transport property measurements show that these two compounds are p-type semiconductors with calculated band gaps of 0.24 eV for the Ag compound and 1.0 eV for the Cu compound.

Different clusters within the Ba4M4−xA2Te9 (M=Cu, Ag, Au; A=Si, Ge) series: Crystal structures and transport properties

“…These bonds are typical single bonds, as found in Na 6 Si 2 Te 6 (2.35 Å) [26] and Na 4 Si 2 Te 5 (2.37 Å) [27], or Tl 6 Ge 2 Te 6 (2.45 Å and 2.46 Å) [28] and K 6 Ge 2 Te 6 (2.49 Å) [29]. With the assumption of A III , the assignment of the valenceelectrons is self-evident: (Ba 2+ ) 4 (M + ) 4 (A III ) 2 (Te 2− ) 9 , as in the previously reported silver and copper germanium tellurides [10]. [10].…”

“…With the assumption of A III , the assignment of the valenceelectrons is self-evident: (Ba 2+ ) 4 (M + ) 4 (A III ) 2 (Te 2− ) 9 , as in the previously reported silver and copper germanium tellurides [10]. [10].…”

“…Recently we reported our first barium copper/silver germanium tellurides Ba 4 M 4−x Ge 2 Te 9 (M = Cu, Ag) [10]. These are the first members of the barium coinage metal germanium telluride system, while a few Ba-Cu/Ag-Ge sulfides and selenides were reported, such as the sulfides BaCu 2 GeS 4 [11], BaAg 2 GeS 4 [12] and BaCu 6 Ge 2 S 8 [13] as well as the selenides BaCu 2 GeSe 4 and BaAg 2 GeSe 4 [14].…”

Vibration uncoupling of germanium with different valence states lowers thermal conductivity of Cs2Ge3Ga6Se14

“…For instance, the Ge 4+ tends to adopt a tetrahedral coordination with four nearly equidistant Ge-Q (Q = S, Se, Te) bonds [12][13][14][15][16][17][18][19], the Ge 3+ usually forms a Ge-Ge metal bond to fulfill its four coordination and generate the characteristic ethane-like Ge 3+ 2 Q 6 dimer [20][21][22][23][24][25][26][27], and the Ge 2+ is often found in an octahedron with six Ge-Q bonds [27,30]. Various arrangements of these structure building units lead to great diversity of structures [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Herein, we report a new compound of the Cs 2 Ge 3 M 6 Q 14 (M = Ga, In; Q = Se, Te) family, Cs 2 Ge 3 Ga 6 Se 14 , in which Ge 3+ and Ge 2+ coexist.…”

The Sodium Antimony Telluridogermanate(III) Na9Sb[Ge2Te6]2

“…Among these are Na 6 Ge 2 Te 6 , crystallizing with the K 6 Sn 2 Te 6 structure type, K 6 Ge 2 S 6 and K 6 Ge 2 Se 6 crystallizing with the K 6 Si 2 Te 6 structure type,, as well as K 6 Ge 2 Te 6 , Cs 6 Ge 2 Te 6 , and Cs 6 Ge 2 Se 6 crystallizing with the K 6 Ge 2 Te 6 structure type . Quaternary compounds Ba 4 M 4–x Tt 2 Te 9 ( M = Cu, Ag, Au; Tt = Si, Ge) have also been reported , . Occasionally, Ge occurs with mixed valence states, e.g.…”