Modulated Linear Tellurium Chains in Ba₃ScTe₅: Synthesis, Crystal Structure, Optical and Resistivity Studies, and Electronic Structure

Abstract

A new ternary telluride, Ba3ScTe5, with a pseudo one-dimensional structure, was synthesized at 1173 K by standard solid-state methods. A single-crystal X-ray diffraction study at 100(2) K shows the structure to be modulated. The structure of the subcell of Ba3ScTe5 crystallizes with two formula units in the hexagonal space group D 3 ,6h−P63/mcm with unit cell dimensions of a = b = 10.1190(5) Å and c = 6.8336(3) Å. The asymmetric unit of the subcell structure consists of four crystallographically independent sites: Ba1 (site symmetry: m2m), Sc1 (−3.m), Te1 (m2m), and Te2 (3.2). Its structure is made up of chains of 1 ,∞[ScTe3 3− ] that are separated by Ba 2+ cations. The Sc atoms are bonded to six Te1 atoms that form a slightly distorted octahedral geometry. The structure of subcell also contains linear infinite chains of Te2 with intermediate Te•••Te interactions. The superstructure of Ba3ScTe5 is incommensurate and was solved in the hexagonal superspace group P−6(00γ)0 with a = 10.1188(3) Å and c = 6.8332(3) Å and a modulation vector of q = 0.3718(2)c*. The arrangement and coordination geometries of atoms in the superstructure are very similar to those in the substructure. However, the main difference is that the infinite chains of Te in the superstructure are distorted owing to the formation of long-and short-bonded pairs of Te atoms. The presence of these chains with intermediate Te•••Te interactions makes the assignment of formal oxidation states arbitrary. The optical absorption study of a polycrystalline sample of Ba3ScTe5 that was synthesized by the stoichiometric reaction of elements at 1173 K reveals a direct bandgap of 1.1(2) eV. The temperature-dependent resistivity study of polycrystalline Ba3ScTe5 shows semiconducting behavior corroborating the optical studies while DFT calculations report a pseudo bandgap of 1.3 eV.

Ternary Chalcogenides BaMxTe2 (M = Cu, Ag): Syntheses, Modulated Crystal Structures, Optical Properties, and Electronic Calculations

“…These bands can be compared with the Ag–Te stretching modes of 80, 110, and 138 cm –1 in Ag 2 Te . The bands at 667 and 732 cm –1 are Ba–Te stretching modes, which are in good agreement with the Ba–Te stretching frequencies in BaIn 2 Te 4 (667 and 732 cm –1 ) and Ba 3 ScTe 5 (671.5 and 730 cm –1 ) …”

“…Among the chalcogens, Te shows the most varied catenations. Te can form infinite chains (Ba3ScTe5, 11 Gd3Cu2Te7, 12 and LaCu0.40Te2 13 ), square nets (EuCu0.66Te2, 14 Na0.2Ag2.8EuTe4, 14 KCu2EuTe4, 14 and K0.33Ba0.67AgTe2 15 ), and neutral Te8 rings (e.g., Cs4Te28) 7 .…”

“…62 The bands at 667 and 732 cm −1 are Ba−Te stretching modes, which are in good agreement with the Ba−Te stretching frequencies in BaIn 2 Te 4 (667 and 732 cm −1 ) 37 and Ba 3 ScTe 5 (671.5 and 730 cm −1 ). 11 Electronic Structure Calculations. Figure 6 shows our calculated total (upper panel) and partial (lower panels) density of states (DOS) for BaCuTe 2 and BaAgTe 2 .…”

“…Among the chalcogens, Te shows the most varied catenations. Te can form infinite chains (Ba 3 ScTe 5 , Gd 3 Cu 2 Te 7 , and LaCu 0.40 Te 2 ), square nets (EuCu 0.66 Te 2 , Na 0.2 Ag 2.8 EuTe 4 , KCu 2 EuTe 4 , and K 0.33 Ba 0.67 AgTe 2 ), and neutral Te 8 rings (e.g., Cs 4 Te 28 ) . In most of these structures, the charge balance of the compounds can be achieved by the Zintl–Klemm concept .…”

Ba3Zr2Cu4S9: the first quaternary phase of the Ba–Zr–Cu–S system

“…14,15 Unlike oxygen, the chalcogens ( Q = S, Se, Te) show pronounce tendency for catenation, i.e. , the chalcogen atoms can form various types of polychalcogen units such as dimers, 16 trimers, 17 infinite chains, 18,19 etc. , within the chalcogenide structures.…”