Dissertation/Thesis Abstract

Polymorphism and Local Structure of Crystalline and Amorphous Zinc-Indium-Tin Oxide (ZITO)
by Hoel, Cathleen Ann, Ph.D., Northwestern University, 2010, 222; 3433582
Abstract (Summary)

The transparent conducting oxide (TCO) and co-substituted solid solution In2-2xZnxSnxO3 (ZITO) has gained attention as a replacement for the industry standard Sn-doped In2O 3 (ITO). Ambient pressure bixbyite and high-pressure corundum ZITO, both crystalline phases, and metastable and amorphous ZITO were synthesized and their local structures were investigated. The short-range structures of the crystalline phases, bixbyite and corundum ZITO, were probed to develop a basis for understanding the short-range structure of amorphous ZITO. The bixbyite structure type (x ≤ 0.4), the most stable phase, was synthesized by solid state reaction in air. Corundum ZITO (x ≤ 0.7), which was first synthesized during the course of this work, was made by high-pressure solid state reaction, by calcination of crystalline oxyhydroxide and hydroxide precursors, and by growth of epitaxial thin films using pulsed-laser deposition. Amorphous ZITO was synthesized by coprecipitation, drying (80 °C) and calcination (300 °C). Both the bixbyite and corundum solid solutions exhibit, as expected, decreasing lattice constants with increasing substitution of the smaller zinc and tin cations. Extended X-ray absorption fine structure (EXAFS) of bixbyite and corundum ZITO revealed that the Zn and Sn local coordination environments remain pseudo-octahedral and that these two ions remain as near metal neighbors at a Zn-Sn distance of ~3.2 Å in corundum. The structure of amorphous ZITO was examined in detail by X-ray diffraction, electron nanodiffraction, total X-ray scattering and X-ray absorption spectroscopy. The structural units present in amorphous ZITO were InO6, SnO6 and ZnO 4 in contrast to the bixbyite and corundum structure types where the basic structural units are all pseudo-octahedral. The In-O, Sn-O and Zn-O bond lengths in amorphous ZITO were all different to owing to the different cationic radii for indium, tin and zinc. The use of mild synthesis conditions favored the formation of tetrahedral ZnO4 with the consequence that crystallization was inhibited. This work shows how the method of synthesis, and the individual cationic radii and charges of indium, zinc and tin, together influence the local and extended structure of In2-2xZnxSn xO3.

Indexing (document details)
Advisor: Poeppelmeier, Kenneth R.
Commitee: Gaillard, Jean-Francois, Weitz, Eric
School: Northwestern University
Department: Chemistry
School Location: United States -- Illinois
Source: DAI-B 72/02, Dissertation Abstracts International
Subjects: Inorganic chemistry
Keywords: Amorphous materials, Cosubstitution, Local structure, Polymorphs, Zinc indium tin oxide
Publication Number: 3433582
ISBN: 978-1-124-39352-0
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