Phasendiagramm des V1-xFexO2-xFx-Systems für o < x ≦ 0,04 / Study of Phase-Diagram in V1-xFexO2-xFx with ο < x ≦ 0.04

Abstract

V1-xFexO2-xFx samples (0 ≤ x ≦ 0.20) have been prepared by solid state reaction in sealed platinum tubes. The temperature-composition phase diagram with 0 < x ≦ 0.04 is found to contain four phases which were determined by X-ray diffraction and 57Fe-Mössbauer measurements. At small (Fe3+, F-) concentrations (x < 0.005) only one Fe-site is seen in the low-temperature M1 phase and one transition from the insulator to metallic phase. For 0.005 ≦ x ≦ 0.008 at temperatures just below the metal-insulator transition a second monoclinic phase M2 is stable in which two Fe-sites are resolved by their electric field gradients and their isomer shifts. These two sites are identified as the Fe atoms on the paired V-V chains and the equispaced V-V chains in the C2/m structure of MAREZIO et al. At higher Fe3+, F- concentrations (x > 0.008) the existence of the intermediate phases M2 and M3, between M1 and the rutile phase, has been confirmed.