MGO-DOPED CR2O3 - SOLUBILITY LIMIT AND THE EFFECT OF DOPING ON THE RESISTIVITY AND ETHANOL SENSITIVITY

The electrical conductance and its alcohol sensitivity of MgO-doped chromia, from pure Cr2O3 to the composition of spinel MgCr2O4, are investigated. The solubility limit of MgO in Cr2O3 can be extended from the previously reported 1 mol% to 2.5 mol%, at a temperature as low as 650-degrees-C, by the sol-gel process. The solubility limit is confirmed by the variation of the unit cell constant for doped chromia. The electrical conductivity increases with increasing MgO content inside the solid-solution range, and decreases outside that range, with the appearance of a conductance peak at the boundary. The alcohol sensitivity of the MgO-doped chromia sensor also varies with MgO content in a similar manner, but decreases inside the solubility limit with increasing MgO doping.