Synthesis and current-voltage characterization of tin dioxide varistors

An overview of the steady state electrical properties of tin dioxide varist ors is presented. The varistors are manufactured in two ways: (1) a ceramic route by mixing and compaction of tin dioxide powder with various dopants and (2) a sol-gel method, where dopants are dispersed in their aqueous solu tions. For a quantitative agreement with the experimental data,the electron ic defect states in the bulk of the tin dioxide grains and at the grain bou ndary interfaces are studied. Scanning electron microscope and x-ray diffra ction are employed to study the morphological and structural aspects of tin dioxide varistors. The effect of various sintering temperatures on their n onohmic or nonlinear characteristics was also investigated. The varistors p repared by the sol-gel method showed high nonlinearity, high density, and h igh threshold voltage properties than the ones produced by the ceramic rout e. This is probably due to a finer grain structure and a better densificati on of dopants along the grain boundaries. (C) 1999 American Vacuum Society. [S0734-2101(99)10804-2].