Abstract
The nuclear magnetic resonance (NMR) spectra of 51V inV 1−xAl xO 2 (0 ⩽ x ⩽ 0.038) has been determined as functions of Al concentration and temperature. The results which are in agreement with differential thermal analysis (DTA), dc electrical conductivity and 6328 A optical reflectance, indicate that the temperature vs Al concentration phase diagram is similar to that previously proposed for Cr-doped VO 2. Comparison of the asymmetry parameters (η) in the electric field gradient and the quadrupole coupling constants (ν Q) show that there exist three distinct phases below the semiconductor to metal (SM) transition temperature. At low Al concentrations (x < 0.02) and low temperatures, the structure may be identified as that of the semiconducting phase of pure VO 2 (Phase I). The T-phase previously reported in pure VO 2 is shown to be the phase occurring just below the SM transition temperature (Phase III). A previously unreported phase (Phase II) exists forx > 0.02 at temperatures between Phases I and III regions.
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