X-ray absorption and diffraction studies of the mixed-phase state of (Cr_xV_1-x)₂O₃

X-ray diffraction and vanadium x-ray absorption near-edge structure (XANES) data have been obtained for (V_1-xCr_x)₂O ₃ samples containing several concentrations of Cr, crossing the metal-insulator transition boundary. For single-phase single-crystal samples our theoretical results are generally in good qualitative agreement with our experimental single-crystal XANES, for both crystal orientations relative to the incident-beam electric vector. However, an anomalous peak occurs for both orientations in the K pre-edge of the single-crystal sample containing 1.2% Cr, a paramagnetic insulator sample that is in the concentration regime corresponding to the room-temperature two-phase (coexistence) region of the phase diagram. Upon increasing the temperature of the 0.4% Cr powdered material to 400 K so that one enters the two-phase region of the phase diagram, a similar peak appears and then diminishes at 600 K. These results, as well as experiments done by others involving room-temperature and low-temperature XANES of a 1.1% Cr sample, suggest that this feature in the V pre-edge structure is associated with the appearance under some circumstances of a small amount of highly distorted VO₆ octahedra in the interface region between coexisting metal and insulating phases. Finally, we find that, for the two-phase regime, the concentration ratio of the metal-to-insulating phase varies between different regions from a sample batch of uniform composition made by the skull melting method.