An in-situ synchrotron study of low positive and negative thermal expansion ceramics

In this dissertation, three families of materials that exhibit low or negative thermal expansion were studied, including NaZr2(PO4)3-type materials, HfW2O8 and ZrW2O8, and rare-earth di-titanates. These materials were studied with high temperature, in-situ synchrotron and/or neutron diffraction to make thermal expansion measurements and determine structural, atomistic unit cell changes leading to the thermal expansion mechanism in each material. During the X-ray diffraction (XRD) experiments, a sample-to-detector distance correction was derived to analyze data more accurately. Samples were synthesized through a low temperature solution-based ceramic synthesis technique called the organic-inorganic steric entrapment method. In chapter 2, a specimen displacement correction method was derived for Debye-Scherrer powder XRD experiments with a flat area detector, which are common at synchrotrons. This correction does not require the use of an internal reference material, is applied during the Rietveld refinement step, and is analogous to the specimen displacement correction equations for Bragg-Brentano geometry experiments. The 2θ correction equation is compared to another specimen displacement correction based on the use of an internal reference material in which new integration and calibration parameters of area detector images are determined. In chapter 3, SrZr4P6O24, CaZr4P6O24, NaTi2P3O12, NaZr2P3O12, MgZr4P6O24, and related solid solutions were synthesized using the organic-inorganic steric entrapment method. The average linear thermal expansion of these materials was between -1 x10-6/℃ and 6 x10-6/℃ from 25 to 1500 ℃, extending the temperature ranges from previous studies by 300 to 700 ℃. High temperature polymorphs of CaZr4P6O24 and SrZr4P6O24 were solved by Fourier difference mapping and Rietveld refinement. This polymorph is present above 1262 and 1268 ℃, respectively. This work measured thermal expansion coefficients to 1500 ℃ for all samples and investigated the differences in thermal expansion mechanisms between polymorphs and between compositions. In chapter 4, the isotropic negative thermal expansion of ZrW2O8 and HfW2O8 was measured from 1105 to 1257 ℃ for ZrW2O8 and from 1105 to 1276 ℃ for HfW2O8. Their linear coefficients of thermal expansion were measured to be -5.52 x 10-6 ℃-1 and -4.87 x 10-6 ℃-1, respectively. This work presents the first in-situ, powder x-ray diffraction measurements of these materials at their thermodynamically stable temperature ranges. The thermal expansion mechanism of increased flexibility and transverse vibrations of the WO4 tetrahedra at temperatures below 775 ℃ appears consistent with the higher temperature region probed here. In chapter 5, the unit-cell parameter and the first temperature dependent coefficient of thermal expansion values for nine of the rare earth di-titanates from room temperature to approximately 1600 ℃, extending previous studies by 400 ℃ to 600 ℃. The monoclinic to orthorhombic transformation temperature in La2Ti2O7 was accurately determined with both in-situ, powder x-ray diffraction and neutron diffraction, giving a simpler approach to measuring this phase transformation at higher resolution than existing single crystal phase transformation studies.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Hulbert, Benjamin S.

Contributors dc:contributor

• Kriven, Waltraud M
• Shoemaker, Daniel P
• Krogstad, Jessica A
• Bellon, Pascal

• Cazr4p6o24
• Nati2p3o12
• Nazr2p3o12
• Mgzr4p6o24
• La2ti2o7
• Pr2ti2o7
• Nd2ti2o7
• Sm2ti2o7
• Gd2ti2o7
• Dy2ti2o7
• Er2ti2o7
• Yb2ti2o7
• Y2ti2o7
• Rare Earth Di-titanate
• Lanthanum Di-titanate
• Ceramic Synthesis
• Steric Entrapment Method
• Ceramic
• Powder Synthesis
• Diffraction
• X-ray
• Xrd
• Crystallography
• Thermal Expansion
• Low Thermal Expansion
• Synchrotron
• Negative Thermal Expansion
• Displacement Correction
• Debye-scherrer
• Nzp
• Nzp-type
• Nasicon
• Zrw2o8
• Hfw2o8
• Zirconium Tungstate
• High Temperature
• Structure Solution
• Fourier Difference Map
• Phase Transformation
• Srzr4p6o24

Statement dc:rights

• © 2023 Benjamin S. Hulbert

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/121482

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F121482