Growth, synthesis, structure, properties and fluorination of barium bismuthate and related oxides

Abstract

This thesis presents a comprehensive study on the synthesis and characterizations of bismuthates, particularly focussing on BaBiO3 and its fluorinated variants, alongside the exploration of strongly correlated oxides such as SrRuO3 and Lanthanum strontium manganite (LSMO). Our synthesis efforts culminated in producing BaBiO3 in multiple forms, including powder, single crystal, polycrystalline thin film, and epitaxial thin film. Through detailed investigations, we observed distinct structural domains affected by growth temperature coexisting in the PLD-grown BaBiO3 (110)/BaF2 (001) epitaxial thin films. Notably, our experiments led to an emergence of an oxygen-deficient phase, BaBiO2.5. In exploring the electronic properties of BaBiO3, specifically the hidden Dirac cone in its band structure, we introduced a novel plasma fluorination technique that replaced oxygen with fluorine, effectively electron-doping the material. This would prompt the Fermi energy level to raise paving the way to access the predicted topological phase. We conducted extensive analyses of the fluorinated thin films to elucidate the electronic modifications caused by fluorination. Our study also highlights the intriguing properties of SrRuO3 and LSMO, two strongly correlated oxides that have gained prominence for their rich fundamental physics and applications in technology. We applied the optimized plasma fluorination strategies on these materials which resulted in significant changes in their electronic and magnetic properties. Lastly, we synthesized the superconducting material BaPb0.75Bi0.25O3, examining both powder and thin film forms fabricated on BaF2 (001) substrates. We also fluorinated the thin films and provided a detailed examination of how fluorination influences the superconducting transition temperature (Tc) and resistance.