Structural transformations around both V and Cr atoms in $({\mathrm{V}}_{1-x}{\mathrm{Cr}}_x{)}_2{\mathrm{O}}_3$ across its metal-insulator transition (MIT) at $x\sim 0.01$ are 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.

• Received 17 June 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.195502