Strong electronic correlations can profoundly alter the phase stabilities and even the geometric structure of materials owing to the close coupling between lattice, spin, and orbital degrees of freedom. Scaling to finite size and inducing compositional variations can thus be used to manipulate the phase stabilities of strongly correlated materials to manifest and tune phenomena such as superconductivity, charge density waves, and colossal metal�insulator transitions. Our goal has been to develop a detailed understanding of the structural phase progression and alterations in local geometric and electronic structure as strongly correlated materials undergo electronic phase transitions. Using the binary vanadium oxide VO2 as a model system, we have tuned the metal�insulator transition temperature between -20 and 70�C through scaling to finite size and incorporation of substitutional dopants. As an example of the interplay of geometric and electronic structure, W and Mo dopant atoms in VO2 create locally symmetric domains, acting as a �Trojan Horse� for nucleation of the high-temperature phase in addition to donating electrons.Mechanistic understanding of the phase transitions has been used to inform the design of novel doping schemes and new compounds. We have discovered the first several compounds in over fifty years to exhibit colossal metal�insulator transitions in close proximity to room temperature. In 1D MxV2O5 bronze phases (M: Pb, K, Cu), charge-ordered patterns of (nominally) V4+ and V5+-cations are arrayed along the anisotropic frameworks. At appropriate charge carrier densities induced by heating or application of a voltage, the charge ordering is melted and the materials are abruptly transformed to a metallic phase. As a practical application of the above-room-temperature metal�insulator transitions of VO2, these materials are being developed as dynamic glazing components for �smart� windows to prevent solar heat gain without blocking daylight, thereby substantially improving the energy efficiency of buildings.

Strongly correlated binary and ternary vanadium oxides: Manipulating electronic instabilities in a low-dimensional world

246th National Meeting (2013)

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