PhD Dissertation Defense

Study of the Phase Separation as Related to the Metal-Insulator Transition in Chromium Doped V₂O₃

The structural transformations around both V and Cr atoms in (V_1-xCr_x)₂O₃ across its metal-insulator transition (MIT) have been studied by extended x-ray absorption fine-structure technique.  Our new results for Cr made possible by the use of a novel x-ray analyzer that we developed reveal the substitutional mechanism of Cr doping.  We find that this system has a buckled structure with short Cr-V and long V-V bonds.  This system of bonds is disordered around the average trigonal lattice ascertained by x-ray diffraction. Such local distortions can result in a long range strain field that sets in around dilute Cr atoms in microscopic regions.  We suggest that such locally strained regions should be insulating even at small x.  The possibility of local insulating regions within a metallic phase, first suggested by Rice and Brinkman in 1972, remains unaccounted for in modern MIT theories.