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Title:Phase equilibria, thermal expansion and symmetry relations within the HfO2-Ta2O5-TiO2-temperature system
Author(s):McCormack, Scott James
Director of Research:Kriven, Waltraud M
Doctoral Committee Chair(s):Kriven, Waltraud M
Doctoral Committee Member(s):Zuo, Jian-Min; Girolami, Gregory S; Shoemaker, Daniel P; Navrotsky, Alexandra
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Phase equilibria
phase diagrams, thermal expansion
powder X-ray diffraction
High temperature
crystal structure solutions
Hafnia
HfO2
Tantala
Ta2O5
Titania
TiO2
Hafnium tantalate
Hf6Ta2O17
Hafnium titanate
HfTiO4
Titanium tantalate
TiTa2O7
Abstract:Most material applications rely on a foundation of knowledge of phase equilibria. In this dissertation, a systematic approach to the rapid production of the high temperature HfO2-Ta2O5-TiO2 phase diagrams is presented that highlights the combined use of: (i) in-situ high temperature X-ray diffraction (up to 3000 ˚C), (ii) Thermal expansion measurements (iii) extraction of atomic motifs with associated material symmetry analysis and (iv) calorimetry. The tools and methodologies developed herein are essential for the development of next generation high temperature materials. The extreme temperatures were achieved by utilizing a quadrupole lamp furnace (QLF) (200 – 2000 ± 4 ˚C) and a conical nozzle levitator system equipped with a CO2 laser (CNL) (700 – 3000 ± 100 ˚C) in conjunction with synchrotron X-ray powder diffraction. These devices allow for (i) phase identification as a function of temperature, (ii) crystal structure determination using the charge flipping algorithm, (iii) extraction of anisotropic co-efficients of thermal expansion from Rietveld analysis, (iv) measurement of lattice variant deformation during phase transformations and finally (v) identification of atomic motifs within material systems that relate the observed the observed crystal structures. Comprehensive energetic studies were performed to accurately determine the stability of compounds and determine critical temperatures for phase transitions. The calorimetry experiments include: (i) thermal arrest measurements utilizing the CNL system to determine solidus and liquidus temperatures, (ii) high temperature oxide solution calorimetry to determine enthalpies of formation and (iii) high temperature differential thermal analysis. More low temperature calorimetry work is required for a complete energetic description. This intersection of phase equilibria and crystallographic symmetry analysis is an innovation methodology that aims to extend our fundamental understanding of material systems. In addition, this methodology has enabled the rapid production of the HfO2-Ta2O5 phase diagram and the solidification pathways within the HfO2-Ta2O5-TiO2 ternary. The dissertation describes in detail how each of these steps were performed, and how all the data was brought together to build innovative atomic and symmetry relationships within the traditional representation of phase equilibria for the HfO2-Ta2O5-TiO2 system.
Issue Date:2019-06-12
Type:Text
URI:http://hdl.handle.net/2142/105748
Rights Information:Copyright 2019 Scott J. McCormack
Date Available in IDEALS:2019-11-26
Date Deposited:2019-08


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