X-ray Absorption Fine Structure Study of the Metal-Insulator Transition in Cr Doped V$_{2}$O$_{3}$*

We have applied the polarized x-ray absorption fine structure (XAFS) spectroscopy to study the series of (V$_{1-x}$Cr$_{x})_{2}$O$_{3}$ where x ranges from 0 to 0.052. At room temperature, the metal-insulator transition (MIT) between paramagnetic metal 1 (PM-1) and paramagnetic insulator (PI) phases occurs as $x$ exceeds 0.01. At elevated temperatures, the second PM phase (PM 2) sets in the metallic samples ($x \quad <$ 0.01). We have obtained V K-edge and Cr K-edge spectra for the samples in the PM1, PM2 and PI phases at different concentrations (from 0.00365 to 0.0052) and temperatures (from 300 K to 673 K). V K-edge X-ray absorption near-edge structure (XANES) data show systematic changes across varies phase boundaries, both temperature and dopant-driven. Polarized Cr K-edge and V K-edge XANES and extended XAFS (EXAFS) data demonstrate, for the first time, that Cr enters the V$_{2}$O$_{3}$ lattice substitutionally, at all concentrations. Contrary to the Cr K-edge, the changes in the V K-edge XANES across the metal-insulator transition are strongly anisotropic. X-ray diffraction (XRD) and temperature dependent XANES and EXAFS results of Cr and V data will be discussed in terms of the possible percolative nature of the MIT in this system.