Theory will be developed for the electronic and vibrational properties of metals, insulators and superconductors, especially crystalline oxides such as copper-and bismuth-oxide superconductors and vanadium-oxide based metal-insulator systems. The underlying motive is to explore the still obscure mechanism for high temperature superconductivity. A secondary motive for the research is to improve understanding of the diverse and poorly understood electrical transport properties of these materials. As a model system barium-bismuth-oxide will be studied in detail. The charge carriers in this insulator are bipolarons. A continuous evolution through an exotic superconducting state to a normal metallic conductor occurs as bismuth is replaced by lead. Polaron and bipolaron models will be developed and tested to model resistivity, Hall coefficient, and superconductivity. Other model systems to be studied are niobium-oxide and vanadium-dioxide. The latter has a metal-insulator transition at a temperature convenient for device applications such as memory elements. The effect of lattice distortion and phonons on the transition will be studied. Thermal conduction will also be studied in a model of amorphous silicon.
