The electrical conductivity of MgO-doped $Cr_2O_3$ and the defect model in nonstoichiometric sesquioxide were investigated as a function of oxygen partial pressure, conductivity measurement temperature, and MgO content.
The rectangular bar specimens were sintered at 1400$^\circ{C}$ for 5 hr keeping oxygen partial pressure as follows: 0.2 atm, 1.0E-2 atm, and 1.0E-4 atm.
The grain size was estimated about 1.0 μm and the microstructure was showed open pores at the initial stage of sintering. Above the solubility limit of MgO in $Cr_2O_3$, the spinel phase($MgO.Cr_2O_3$) was formed by the reaction of MgO and $Cr_2O_3$. The solubility limit of MgO in $Cr_2O_3$ was increased with oxygen partial pressure.
The DC electrical conductivity of doped $Cr_2O_3$ was measured by four probe method varying the oxygen partial pressure (1.0E-4 atm-1.0 atm) and temperature (600$^\circ{C}$-1400$^\circ{C}$). The electrical conductivity of MgO-doped $Cr_2O_3$ was increased with oxygen partial pressure and conductivity measurement temperature. The electrical conductivity of MgO-doped $Cr_2O_3$ within solubility limit was increased with MgO content because of the creation of the electron hole and the annihilation of the chromium vacancy. Above the solubility limit, however, it was decreased with increasing MgO content owing to the formation of the spinel phase ($MgO .Cr_2O_3$).
