In this research, the microstructure, dielectric, and non-Ohmic properties of (Cr, Nb) co-doped SnO2 ceramics, (Cr0.5, Nb0.5)xSn1-xO2 with x% = 0, 0.5, 1.0, 2.0, 5.0, and 10.0, as a colossal dielectric material and a prospective alternative to co-doped TiO2 ceramics were studied. The X-ray diffraction results indicated that in all compositions, the cassiterite phase was achieved without any secondary phases. Moreover, field-emission secondary electron microscopy showed that the microstructure of samples has different morphologies including typical grains, enlarged grains and prism-like grains microstructure for various sintered samples. The maximum dielectric constant (2737) accompanied by the lowest dielectric loss (0.04) at the frequency of 1 kHz was obtained for (Cr0.5, Nb0.5)0.02Sn0.98O2. The all co-doped SnO2 samples except for x = 10.0 showed non-Ohmic properties. Based on the observed non-Ohmic properties, the mechanism of dielectric properties of (Cr, Nb)-doped SnO2 ceramics was attributed to the internal barrier layer capacitor (IBLC) model. According to this model, samples with higher breakdown electric field demonstrate the better stability of dielectric properties, when DC bias voltage is applied.
