Method for preparing semiconducting ceramics, made of metal oxides, preferably tin oxide, used particularly for varistors

The dopants are oxides of cobalt, manganese, niobium, tantalum, zinc and chromium. The tin oxide semiconductor contains tin oxide (98.24%), cobalt oxide (0.05%), manganese oxide (1.69%), niobium oxide (0.01%), tantalum oxide (0.01%) and chromium oxide (0.01-3%). The alloy powder is prepared by solidification of mixture or molten alloy. The homogeneous molten alloy is pulverized and atomized by liquid, soaks and neutral or reducing gas such as hydrogen, nitrogen, argon, or their mixtures. Mixture or molten metal alloy is passed in an ingot mold under a neutral or reducing atmosphere and realized in solid phase by abrasion or crushing. The alloy powder is separated in granulometric cuttings and oxidized with 64 weight %. The partial or total oxidation of alloy powder particles is carried out while putting the particles in contact with a gas oxidization at 400-950[deg]C for 2 seconds and realized by compacting the powder in the form of pastilles e.g. by cold pressing. The powder is sintered at 1100-1350[deg]C for 30 minutes. The gas oxidization contains oxygen, carbon dioxide and/or mixture of CO and CO 2. Procédé de préparation d'une céramique semi-conductrice à base d'oxyde d'étain SnO 2 dopé, par un procédé de type « ODAP » (Oxydation Directe d'un Alliage Précurseur) appliqué à un alliage d'étain et de métaux dopants ; ou par un procédé de type « ODAP » appliqué à l'étain, les métaux dopants étant ajoutés sous la forme d'oxydes dans la poudre soumise au frittage.