Study of Functional Complex Oxides at High Pressure-Temperature Conditions

Complex oxides are a diverse family of functional materials whose stability and transformations under extreme conditions are central to chemistry, energy research, and the design of novel compounds. This dissertation focuses on lithium cobalt oxyfluoride (Li2CoO2F), a Li-rich disordered rock-salt cathode, together with other representative complex oxides studied under high pressures and temperatures. Synchrotron X-ray diffraction, Raman spectroscopy, neutron scattering, and first-principles calculations were used to probe the structural response of Li2CoO2F across multiple length scales. These studies reveal how fluorination and Li enrichment promote local spinel-like motifs, stabilize metastable frameworks, and modify the elastic behavior under compression and heating. Complementary work on PbTiO3 demonstrates how kinetic barriers and thermodynamic driving forces combine to stabilize unexpected dissociation products, including a previously unreported PbO polymorph at megabar pressures. High-entropy oxide nanoribbons were also examined, with high-pressure experiments showing transformations from orthorhombic to cubic and ultimately amorphous states, underscoring their structural resilience and entropic complexity. Overall, this work provides new insight into the structural response of Li2CoO2F and related oxides under extreme conditions, highlighting how fluorination and Li enrichment influence their stability.

Author dc:creator

• Husam Farraj (23292013)

• Chemistry
• Inorganic

Statement dc:rights

• In Copyright
• Open Access after 2028-01-01

DOI dc:identifier

https://doi.org/10.25417/uic.31451635.v1

OAI identifier oai:identifier

oai:figshare.com:article/31451635