**5. Conclusions**

The study of SnO2-based varistor systems is recent, so a huge amount of published papers do not exist. Research involving the material is mostly related to the understanding of the influence of dopants on densification materials prepared by mixing oxide and the change in the parameters of the potential barrier formed at grain boundary region, which is directly related to the nonlinear coefficient and determines the quality of varistor ceramics. The bivalent metals (Ba2+, Ca2+, Co2+, Zn2+, and others) have proven action as a densifying agent since the defects generated by their addition to the ceramic matrix assist in mass diffusion. The addition of trivalent ions (Cr3+, Er3+, and others) causes the increase of nonlinearity coefficient due to the higher adsorption electron acceptor species on the surface of the grain boundary and thus causing a reduction in conductivity of the material. The new methodologies for the chemical synthesis of ceramic powder promote the homogeneous distribution of dopants into the ceramic matrix and reduce segregation and the formation of secondary phases, confirmed by XRD analysis, which are harmful factors on the electrical properties of the varistor and facilitate the integration of the material in today's electronic devices electrical protection. The use of microwave oven is a new processing step aimed to reduce the time and temperature of sintering step and can be considered a promising procedure for the varistors production. The preparation of varistors as film emerges as a new possibility in order to facilitate integration of this material in electronic circuits.
