Frustrated Magnetism and Electronic Properties of Hollandite Oxide Materials

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Microporous transition metal oxides with the hollandite structure type have been prepared by standard solid-state techniques with varying compositions. With a nominal formula of AxM8O16 and a framework of edge and corner-sharing MO6 octahedra, hollandites feature a pseudo-one dimensional tunnel occupied loosely by cation A. The metastability of these open-framework materials, combined with the ability of accommodating a variety of redox-active transition metals leads to unique and indispensable properties. Inherent to the triangular connectivity of the M cations in the hollandite framework, these materials frequently exhibit frustrated magnetic behavior.

This thesis demonstrates that it is possible to significantly affect the magnetic and transport properties of these microporous materials through tuning of their chemical compositions. We have shown that it is possible to synthesize polycrystalline and single crystal hollandite materials under ambient conditions utilizing salt flux techniques. Our efforts to characterize the structure-property relationships provide some of the first magnetic structure determinations of these complex frameworks. The interesting behavior of these materials is a result of the interplay between charge, orbital, and spin degrees of freedom.

This work shows that the hollandite framework is quite versatile, leading to the real possibility of tuning the material properties to achieve desired effects and opening up many potential applications for these microporous oxides.