GB1397782A - Oxide varistor - Google Patents

Abstract

1397782 Semi-conductor varistors TOKYO SHIBAURA ELECTRIC CO Ltd 23 May 1972 [24 May 1971 10 June 1971 1 Feb 1972] 24112/72 Heading H1K A varistor comprises a basic composition which in 100 mol per cent contains 87 to 12 mol per cent ZnO, 1 to 30 mol per cent of Sb 2 O 3 and 12 to 87 mol per cent of at least one metal oxide MeO selected from the group MgO, CoO, NiO, BaO, SrO, CaO, MnO, FeO, CuO; with an additive of Bi 2 O 3 to the extent of 0À5 to 10% w/w of the basic composition, the metal oxide component forming at least 14% mol of the base composition when it consists of CoO together with BaO and/or MnO. In preparation the oxides are weighed out, mixed in a ball mill, sintered at 600-850‹ C., and again ball milled; and may be derived from compounds oxidized by heat, e.g. hydroxides, carbonates, oxalates. The powder is admixed with, e.g. polyvinyl alcohol binder, disc moulded under pressure, and sintered in air at 1000‹ to 1400‹ C. Electrodes of Ag or In-Ga alloy may be applied, and it is shown that the nonlinear characteristics are derived from a large number of agglomerations of the boundary phases of sintered fine crystals (Figs. 8a, 8b, not shown). Numerous examples are quoted, and the voltage current characteristics related to the proportions of Sb 2 O 3 with different metal oxides MeO, to the proportions of ZnO to MeO, and to the proportion w/w of Bi 2 O 3 are given (Figs. 1 to 7, not shown).