<b>Effect of Pr₆O₁₁ doping in electrical and microstructural properties of SnO₂-based varistors<b>

Resumo

The influence of the dopant Pr₆O₁₁ was investigated with regard to the electrical and microstructural properties of the system (98.95-x)%SnO₂.1.0%CoO.0.05%Ta₂O₅.x%Pr₆O_11, where x = 0.05%, 0.10%, 0.30% and 0.50% in mol. Pr₆O₁₁ doping modifies the electrical behavior of the ceramics. The electrical parameters were: α = 8.0, E_B = 319 V cm^-1 and V_b = 0.66 V barrier^-1 for the system without Pr₆O₁₁ and α = 17.0, E_B = 853 V cm^-1 and V_b = 1.15 V barrier^-1 with the addition of 0.10% in mol Pr₆O₁₁. The system with 0.05% in mol Pr₆O₁₁ had the same non-linearity coefficient α as the system with 0.10% in mol. However, breakdown electrical field and voltage per barrier rates were lower (E_B = 708 V cm^-1 and V_b = 0.98 V barrier^-1). The low rates in the breakdown electrical field enabled the varistor systems under study to be used in protection systems for low-voltage energy grids. In the case of Pr₆O₁₁ concentrations above 0.10% in mol, the presence of the dopant became deleterious to the varistor´s electrical characteristics. This effect was due to an increase in praseodymium stannate (Pr₂Sn₂O₇) secondary phase. The crystalline phase coupled to the cassiterite (SnO₂) phase was found with XRD and SEM/EDS and quantified by Rietveld´s refining method.