CHROMIUM DIOXIDE (CRO2) AND COMPOSITES OF CHROMIUM DIOXIDE AND OTHER OXIDES OF CHROMIUM SUCH AS CRO2/CR2O3 AND CRO2/CR2O5 AND PROCESS FOR MANUFACTURING THE SAME

摘要

A novel process for preparing chromium dioxide of substantially high purity as well as composites of CrO₂/Cr₂O₃ and CrO₂/Cr₂O₅ following a sequence of simple steps. The process does not require pressure as a control parameter during the process of synthesis. No chemical modifier has been used to bring down the working pressure during synthesis. Fairly hard sintered pellets of CrO₂ can be obtained without introducing any detectable impurity phase that usually appears during the process of sintering. Further, CrO₂/Cr₂O₃ and CrO₂/Cr₂O₅ composites have also been prepared where the fraction of insulating Cr₂O₃ or Cr₂O₅ in metallic CrO₂ can be easily controlled. Significant negative magnetoresistance is found in pure CrO₂ (5% MR) as well as CrO₂/Cr₂O₃ (33% MR) composites near room temperature. The MR studies on the CrO₂/Cr₂O₅ composites have been done and significant negative MR (22%) has been found in CrO₂/Cr₂O₅ composites near room temperature.