Phase equilibria, thermal expansion and symmetry relations within the HfO2-Ta2O5-TiO2-temperature system

McCormack, Scott James

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https://hdl.handle.net/2142/105748 Copy

Description

Title

Phase equilibria, thermal expansion and symmetry relations within the HfO2-Ta2O5-TiO2-temperature system

Author(s)

McCormack, Scott James

Issue Date

2019-06-12

Director of Research (if dissertation) or Advisor (if thesis)

Kriven, Waltraud M

Doctoral Committee Chair(s)

Kriven, Waltraud M

Committee Member(s)

• Zuo, Jian-Min
• Girolami, Gregory S
• Shoemaker, Daniel P
• Navrotsky, Alexandra

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(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.

Graduation Semester

2019-08

Type of Resource

text

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http://hdl.handle.net/2142/105748

Copyright and License Information

Copyright 2019 Scott J. McCormack

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