Taiyo Yuden Co., Ltd.

Susumu Hirooka

Nobutatsu Yamaoka

Masaru Masuyama

Ceramic materials suitable for use in varistors, enabling the same to function not only as such but also as capacitors. The ceramic materials comprise a major proportion of SrTiO.sub.3, the balance being: (1) at least one of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Y.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Sm.sub.2 O.sub.3, Eu.sub.2 O.sub.3, and Dy.sub.2 O.sub.3, for making the materials semiconductive; (2) Na.sub.2 O, for making surge-proof the varistors made from the ceramic materials and for improving their nonlinearity coefficients; and (3) Al.sub.2 O.sub.3, for improving the temperature dependences of the varistor voltages, as well as nonlinearity coefficients, of the varistors. Optionally the ceramic materials may further contain one or more of Ag.sub.2 O, CuO, MnO.sub.2, and SiO.sub.2, for still higher nonlinearity coefficients. Containing Al.sub.2 O.sub.3 in proportions ranging from 0.01 to 1.50 mole parts with respect to 100 mole parts of SrTiO.sub.3, the ceramic compositions make possible the provision of varistors having varistor voltages that hardly change in a temperature range as wide as, for example, from -40.degree. to +120.degree. C.

Semiconductive ceramic materials with a voltage-dependent nonlinear

Ceramic materials suitable for use in varistors, consisting essentially of a major proportion of SrTiO.sub.3, the balance being (1) at least one of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Y.sub.2 O.sub.3, Sm.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Eu.sub.2 O.sub.3, and Dy.sub.2 O.sub.3, for making the materials semiconductive, and (2) Na.sub.2 O, for making surge-proof the varistors made from the ceramic materials. As desired, the compositions may further include one or more of Ag.sub.2 O, CuO, MnO.sub.2, and SiO.sub.2 for a higher nonlinearity coefficient. Containing Na.sub.2 O in proportions ranging from approximately 0.02 to 2.50 mole parts, the ceramic compositions make possible the provision of varistors suffering little from current or voltage surges in use.

Ceramic materials with a voltage-dependent nonlinear resistance

Semiconductive ceramic materials suitable for use in varistors, consisting essentially of a major proportion of Sr(.sub.1-x)Ca.sub.x TiO.sub.3, where x is from about 0.01 to about 0.50, the balance being at least one of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Y.sub.2 O.sub.3, Sm.sub.2 O.sub.3, Pr.sub.6 O.sub.11 and Dy.sub.2 O.sub.3, and Na.sub.2 O. The ceramic materials may further comprise a minor proportion of at least one of Ag.sub.2 O, CuO, MnO.sub.2 and SiO.sub.2, and/or a minor proportion of Al.sub.2 O.sub.3. For the fabrication of ceramic bodies of the above compositions there are prepared mixtures of the noted ingredients in powdered form in various possible combinations, plus an organic binder. The mixtures are molded under pressure into desired shape. The moldings are first fired in a reductive or neutral atmosphere and then refired in an oxidative atmosphere. Na.sub.2 O can be included in the initial mixtures in the form of Na.sub.2 O itself and/or other Na compound such as NaF. Alternatively, either Na.sub.2 O itself or NaF is pasted and coated on the moldings after the initial firing thereof. The subsequent refiring of the coated moldings causes thermal diffusion of Na.sub.2 O therein.

Semiconductive ceramic materials suitable for use in varistors, consisting essentially of a major proportion of Sr.sub.(1-x) Ca.sub.x TiO.sub.3, where x is from about 0.01 to about 0.50, the balance being at least one of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Y.sub.2 O.sub.3, Sm.sub.2 O.sub.3, Pr.sub.6 O.sub.11 and Dy.sub.2 O.sub.3, and Na.sub.2 O. The ceramic materials may further comprise a minor proportion of at least one of Ag.sub.2 O, CuO, MnO.sub.2 and SiO.sub.2, and/or a minor proportion of Al.sub.2 O.sub.3. For the fabrication of ceramic bodies of the above compositions there are prepared mixtures of the noted ingredients in powdered form in various possible combinations, plus an organic binder. The mixtures are molded under pressure into desired shape. The moldings are first fired in a reductive or neutral atmosphere and then refired in an oxidative atmosphere. Na.sub.2 O can be included in the initial mixtures in the form of Na.sub.2 O itself and/or other Na compound such as NaF. Alternatively, either Na.sub.2 O itself or NaF is pasted and coated on the moldings after the initial firing thereof. The subsequent refiring of the coated moldings causes thermal diffusion of Na.sub.2 O therein.

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Takasaki, Japan

Susumu Hirooka