The tungsten bronze family is an incredibly diverse system of electronically tunable perovskite-derived materials. One of the many interesting properties observed in this system is type-II superconductivity.
The tunability of tungsten bronzes makes them an ideal playground for studying
type-II superconductivity and moving toward enhancement of the superconducting transition temperature, Tc. This thesis seeks to build up a predictive understanding of type-II superconductivity by manipulating the basic tungsten bronzes under the complex doping schemes of poor metal intercalation and oxygen substitution for fluorine. In the course of these studies, I report Tc enhancement in the hexagonal tungsten bronze system InxWO3 and probable new superconducting materials in the poor metal intergrowth tungsten bronzes. On the other hand, the fluorine-doped perovskite phase NbO2−x2F1−x is found to not be a metallic conductor at all, despite simple band
structure considerations. In the course of studying why NbO2−x2F1−x does not electrically conduct like other bronze phases do, numerous physical phenomena are uncovered in this system: a structural
phase transition, a pronounced negative coefficient of thermal expansion in the range 10 K - 295 K, 3D variable range hopping electrical conduction, and probable spin-glass ordering. While alkali metal dopants are generally thought of as simple electron donors, poor metals and fluorine
atoms are both found to participate in the band structures of bronzes at the Fermi level, leading to dramatic and complex dependence of physical properties on doping level.
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