X-ray and neutron scattering studies of microstructure and dynamics in VO$_{2}$*

Vanadium dioxide is a strongly correlated material that exhibits a well-studied, but poorly understood, metal-insulator transition coupled with a tetragonal-monoclinic structural phase transition near 340 K. We have combined synchrotron x-ray and spallation neutron scattering measurements to investigate microstructure and lattice dynamics in VO$_{2}$. Submicron-resolution x-ray microdiffraction studies reveal local phase coexistence driven by strain effects within individual single-microcrystals. Macroscopic diffuse scattering and inelastic x-ray and neutron scattering measurements reveal unusual features in the rutile phonon dispersions at particular locations in reciprocal space, including temperature-dependent dispersions near the R-point. Comparisons of measurements with ab initio molecular dynamics calculations indicate that anharmonicity plays a central role in determining the lattice vibrations and hence physical properties in this system.