Distorted Square Nets of Tellurium in the Novel Quaternary Polytelluride K0.33Ba0.67AgTe2

Xiang Zhang, Jing Li, Hong You Guo, Mercouri G. Kanatzidis, Jing Li, Brendan Foran, Stephen Lee, Tim Hogan, Carl R. Kannewurf

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Abstract

The synthesis, structure, and band structure analysis of the quaternary compound K0.33Ba0.67AgTe2are reported. Crystals of K0.33Ba0.67AgTe2were obtained in a K2Te/BaTe/Te flux by the reaction of 1 mmol of K2Te, 0.5 mmol of BaTe, 0.5 mmol of Ag, and 4 mmol of Te in an evacuated Pyrex tube at 450 °C for 3 days followed by a slow cooling to 150 °C. The compound has a substructure in the tetragonal space group I4/mmm (no. 139) with asub = 4.624 (2) Å, csub = 23.326 (4) Å, V = 498.7 (3) Å3, at 20 °C (Mo Ka radiation): Z = 4, Dcalc = 6.23 g/cm3, 20max = 50°, data collected: 592, independent data: 172, observed with I > 3σ (I): 108, variables: 13, final R = 0.054, Rw= 0.067. K0.33Ba0.67AgTe2has a lamellar structure related to that of Na1.9Cu2Se2•CCu2O. The substructure contains a readily recognizable [Te2]4/3-square net. The closest Te-Te distance in the net is 3.269 (2) A, not a full covalent bond, but too short for a simple van der Waals contact. While it is predicted that the square [Te2]4/3-net has metallic properties, the experimental data show a semiconductor behavior which has its origins in a structural distortion. Electron diffraction measurements reveal the presence of two different but related superstructures; an incommensurate orthorhombic superstructure of the tetragonal cell with asuper = 2.84aSUb, bSuper = bsub, and csuper = cSub, and Acommensurate tetragonal superstructure with aSuper = 3aSUb, bsuper = 36SUb, and csuper = csub. Both extended-Hiickel and Hückel calculations suggest that this distortion is a charge density wave. In the case of the incommensurate cell, the theoretically predicted supercell corresponds to the experimentally observed. We also used the μ2-scaled Hückel method to predict the actual atomic positions within the supercell. The theoretically predicted superstructures have calculated diffraction patterns similar to the experimentally observed ones.

Original languageEnglish
Pages (from-to)10513-10520
Number of pages8
JournalJournal of the American Chemical Society
Volume117
Issue number42
DOIs
Publication statusPublished - Jan 1 1995

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ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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