Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Hugo F. Franzen

Abstract

A study of the effect of the addition of nonmetal interstitial atoms to zirconium-nickel compounds has led to the discovery of several new phases and the elucidation of general features of the bonding within these phases. In addition to the new phases discovered. a single crystal X-ray study was carried out for the previously reported compound Zr[subscript]3NiO (Cmcm, a = 3.353A, b = 11.013A, c = 8.755A); Zr[subscript]4Ni[subscript]2O is a high temperature phase, forming in samples annealed at 1250°C. It crystallizes with the filled Ti[subscript]2Ni type structure (Fd3m, a = 12.1970A). Band calculations of the extended Huckel type led to the prediction and then confirmation of additional phases in more electron rich systems. Other phases studied by single crystal X-ray diffraction are Zr[subscript]6Ni[subscript]4Ti[subscript]2O[subscript]0.6 (a = 12.0299A), Nb[subscript]6Ni[subscript]6O (a = 11.2117A), and Nb[subscript]6Ni[subscript]4Ta[subscript]2O[subscript]2 (a = 11.5813A). Phases identified by powder diffraction film data are Nb[subscript]4Ni[subscript]2O (a = 11.5933A), Zr[subscript]4Cu[subscript]2O (a = 12.2659A), and Zr[subscript]6Co[subscript]4Ti[subscript]2O (a = 11.8649A). The band calculations do not explain the differences of oxygen ordering observed within these phases, but they do point out several features of general bonding characteristics;New zirconium kappa phases, in space group P6[subscript]3/mmc, have been found. These new phases are Zr[subscript]9Mo[subscript]4SO[subscript]x (a = 8.685A, c = 8.571A), Zr[subscript]9W[subscript]4SO[subscript]x (a = 8.671A, c = 8.607A), and Zr[subscript]9W[subscript]4(S,Ni)O[subscript]3 (a = 8.688A, c = 8.558A). Kappa phases show the ability of filling both trigonal prismatic and octahedral sites simultaneously. Sulfur and nickel also demonstrate the ability to substitute on the same site;A new structure type was discovered with the compound Zr[subscript]9Ni[subscript]6TiSiO[subscript]1.8. This structure consists of a metal framework of zirconium and nickel, with titanium and silicon filling icosahedral sites. The structure can be viewed as a distortion of the kappa phase (P3m1, a = 8.2778A, c = 7.441A);A common feature in all of these interstitially stabilized phases is the coordination of oxygen in zirconium octahedra. There are no nickel-oxygen interactions. In Zr[subscript]3NiO the octahedra share vertices and edges. In all of the new phases they share faces. The face sharing octahedra form large rings, forming two-dimensional networks in the kappa phases and Zr[subscript]6Ni[subscript]6TiSiO[subscript]1.8, and a three-dimensional network in the Ti[subscript]2Ni type structures. Icosahedral units fill the spaces between the octahedral networks.

DOI

https://doi.org/10.31274/rtd-180813-11130

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Richard Alan Mackay

Language

en

Proquest ID

AAI9334997

File Format

application/pdf

File Size

133 pages

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