Distorted square nets of tellurium in the novel quaternary polytelluride K0.33Ba0.67AgTe2

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

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Abstract

The synthesis, structure, and band structure analysis of the quaternary compound K0.33Ba0.67AgTe2 are reported. Crystals of K0.33Ba0.67AgTe2 were 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 Kα radiation): Z = 4, Dcalc = 6.23 g/cm3, 2θmax = 50°, data collected: 592, independent data: 172, observed with I > 3σ(I): 108, variables: 13, final R = 0.054, Rw = 0.067. K0.33Ba0.67AgTe2 has a lamellar structure related to that of Na1.9Cu2Se2•Cu2O. The substructure contains a readily recognizable [Te2]4/3- square net. The closest Te-Te distance in the net is 3.269(2) Å, 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 a commensurate tetragonal superstructure with asuper = 3asub, bsuper = 3bsub, and csuper = csub. Both extended-Hückel 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
Publication statusPublished - Oct 25 1995

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Tellurium
Charge density waves
Semiconductors
Covalent bonds
Lamellar structures
Electron diffraction
Band structure
Diffraction patterns
Electrons
Radiation
Semiconductor materials
Fluxes
Cooling
Crystals

ASJC Scopus subject areas

  • Chemistry(all)

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Distorted square nets of tellurium in the novel quaternary polytelluride K0.33Ba0.67AgTe2. / Zhang, Xiang; Li, Jing; Foran, Brendan; Kanatzidis, Mercouri G; Guo, Hong You; Hogan, Tim; Kannewurf, Carl R.; Kanatzidis, Mercouri G.

In: Journal of the American Chemical Society, Vol. 117, No. 42, 25.10.1995, p. 10513-10520.

Research output: Contribution to journalArticle

Zhang, X, Li, J, Foran, B, Kanatzidis, MG, Guo, HY, Hogan, T, Kannewurf, CR & Kanatzidis, MG 1995, 'Distorted square nets of tellurium in the novel quaternary polytelluride K0.33Ba0.67AgTe2', Journal of the American Chemical Society, vol. 117, no. 42, pp. 10513-10520.
Zhang, Xiang ; Li, Jing ; Foran, Brendan ; Kanatzidis, Mercouri G ; Guo, Hong You ; Hogan, Tim ; Kannewurf, Carl R. ; Kanatzidis, Mercouri G. / Distorted square nets of tellurium in the novel quaternary polytelluride K0.33Ba0.67AgTe2. In: Journal of the American Chemical Society. 1995 ; Vol. 117, No. 42. pp. 10513-10520.
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title = "Distorted square nets of tellurium in the novel quaternary polytelluride K0.33Ba0.67AgTe2",
abstract = "The synthesis, structure, and band structure analysis of the quaternary compound K0.33Ba0.67AgTe2 are reported. Crystals of K0.33Ba0.67AgTe2 were 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) {\AA}, csub = 23.326(4) {\AA}, V = 498.7(3) {\AA}3, at 20°C (Mo Kα radiation): Z = 4, Dcalc = 6.23 g/cm3, 2θmax = 50°, data collected: 592, independent data: 172, observed with I > 3σ(I): 108, variables: 13, final R = 0.054, Rw = 0.067. K0.33Ba0.67AgTe2 has a lamellar structure related to that of Na1.9Cu2Se2•Cu2O. The substructure contains a readily recognizable [Te2]4/3- square net. The closest Te-Te distance in the net is 3.269(2) {\AA}, 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 a commensurate tetragonal superstructure with asuper = 3asub, bsuper = 3bsub, and csuper = csub. Both extended-H{\"u}ckel and H{\"u}ckel 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 H{\"u}ckel method to predict the actual atomic positions within the supercell. The theoretically predicted superstructures have calculated diffraction patterns similar to the experimentally observed ones.",
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AU - Zhang, Xiang

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AU - Foran, Brendan

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AU - Guo, Hong You

AU - Hogan, Tim

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AU - Kanatzidis, Mercouri G.

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N2 - The synthesis, structure, and band structure analysis of the quaternary compound K0.33Ba0.67AgTe2 are reported. Crystals of K0.33Ba0.67AgTe2 were 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 Kα radiation): Z = 4, Dcalc = 6.23 g/cm3, 2θmax = 50°, data collected: 592, independent data: 172, observed with I > 3σ(I): 108, variables: 13, final R = 0.054, Rw = 0.067. K0.33Ba0.67AgTe2 has a lamellar structure related to that of Na1.9Cu2Se2•Cu2O. The substructure contains a readily recognizable [Te2]4/3- square net. The closest Te-Te distance in the net is 3.269(2) Å, 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 a commensurate tetragonal superstructure with asuper = 3asub, bsuper = 3bsub, and csuper = csub. Both extended-Hückel 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.

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