Date of Award
Doctor of Philosophy
Hugo F. Franzen
Six new solid solution type compounds have been prepared using high temperature techniques and characterized by means of single crystal x-ray techniques during a study of the metal-rich region of the ternary Ta-Nb-S system;The structures of Nb[subscript] xTa[subscript] 11-xS[subscript]4 (x ≈ 4.92; Pnma; z = 4; a = 31.2100(54), b = 3.3507(7) and c = 9.5918(19)A) and Nb[subscript] 12-xTa[subscript] xS[subscript]4 (x ≈ 5.26; Pnma; Z = 4; a = 9.5911(26), b = 3.3637(10) and c = 32.8251(74)A) are reminiscent of niobium-rich sulfides, rather than of tantalum-rich sulfides. The coordinations of sulfur are capped trigonal prismatic while the metal coordinations are capped distorted cubic prismatic for Nb[subscript] xTa[subscript] 11-xS[subscript]4, and capped distorted cubic prismatic and pentagonal prismatic for Nb[subscript] 12-xTa[subscript] xS[subscript]4;The structures of Nb[subscript] xTa[subscript] 5-xS[subscript]2 (x ≈ 1.72; I4/mmm; Z = 2; a = 3.3203(9) and c = 21. 619(12)A) and Nb[subscript] xTa[subscript] 2-xS (x ≈ 0.95; P4/nmm; Z = 2; a = 3.3304(7) and c = 9.0928(94)A) contain homoatomic layers sequenced S-M3-M2-M1-M2-M3-S (M is mixed Nb, Ta) generating seven-layer sheets and S-M2-M1-M1-M2-S generating six-layer sheets, respectively, stacked along (001). Both of the structures are closely related to bcc. Weak S-S interactions at 3.26 and 3.19A between sheets contrast with the M-M binding within and between the sheets in these two novel layered compounds. The former are presumably responsible for the observed graphitic slippage of the samples;Nb[subscript] 21-xTa[subscript] xS[subscript]8 (x ≈ 6.2; I4/mmm; Z = 2; a = 16.817(2) and c = 3.3450(9)A) and Nb[subscript] xTa[subscript] 2-xS (x ≈ 0.20; Pbcm; Z = 12; a = 7.3724(11), b = 5.5757 and c = 15.1981(23)A) are isostructural with Nb[subscript]21S[subscript]8 and Ta[subscript]2S, respectively;Extended Huckel band calculations were carried out for two layered compounds, Nb[subscript] xTa[subscript] 5-xS[subscript]2 (x ≈ 1.72) and Nb[subscript] xTa[subscript] 2-xS (x ≈ 0.95). Based upon band calculations metallic properties can be expected for these two layered compounds. The relative preference of the metal sites for the two metal elements (Ta, Nb) in two layered compounds is explained by the results of the band calculations.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Yao, Xiaoqiang, "Structural studies of the metal-rich region in the ternary Ta-Nb-S system " (1991). Retrospective Theses and Dissertations. 9790.