Electrical Transitions in Pure and Doped V2o3

Extensive electrical and thermal studies on transitions in (CrxV1-x)2O3, 0 ⩽ x ⩽ 0.03, and in (TixV1-x)2O3, 0 ⩽ x ⩽ 0.06, have been undertaken. An increase in Cr-doping (0 ⩽ x ⩽ 0.018) raises the temperature of the low-temperature transition and elevates the resistivity of the metallic phase ; it first sharpens and later diminishes the high-temperature transition. The latter (transition) in 1 at. % of Cr-doped V2O3 is characterized by stepwise discontinuities in resistivity and by sharp spikes in DSC scans. Experimental work on Ti-doped V2O3 shows that the size and temperature of the low-temperature transition (Tt) diminish drastically with increasing Ti content. At a Ti concentration of ca. 5.6 at. %, Tt drops abruptly from 35 to (presumably) 0 K. The activation energy of the semiconducting phase diminishes nearly exponentially to zero in this composition range. The above findings, in conjunction with other evidence obtained from resistivity and heat capacity measurements, suggest that the high-temperature transition in (CrxV1-x)2O3 system is not readily compatible with the Mott transition model but is consistent with the existence of Overhauser charge density waves. Further, the (TixV1-x)2O3 system, whose structure is essentially unaltered by Ti doping, provides a testing ground for theories on the abrupt disappearance of metal-insulator transitions.