Barium titanate semiconductive ceramic

Abstract

The present invention provides barium titanate semiconductive ceramic having low specific resistance at room temperature and high withstand voltage, which fully satisfies the demand for enhancing withstand voltage. The average ceramic grain size of the barium titanate semiconductive ceramic is controlled to about 0.9 μm or less. By this control, the ceramic possesses low specific resistance at room temperature and high withstand voltage fully satisfying a recent demand for enhancing withstand voltage and may suitably used for applications such as controlling temperature and limiting current, or in exothermic devices for constant temperature. Accordingly, the barium titanate semiconductive ceramic enables an apparatus using the same to have enhanced performance and reduced size.

What is claimed is:  
     
         1 . A powder for producing a barium titanate semiconductive ceramic having an average ceramic grain size of about 0.9 μm or less, which powder comprises a barium titanate powder having a grain size of about 0.1 μm or less, a cubic system crystal structure and a lattice constant of 4.02 angstroms or more, and containing at least one semiconducting agent in the form of solid solution.  
     
     
         2 . The powder according to  claim 1 , wherein the semiconducting agent is selected from the group consisting of rare earth metal elements and transition elements.  
     
     
         3 . The powder according to  claim 2 , wherein the semiconducting agent is La.  
     
     
         4 . The powder according to  claim 1 , wherein the barium titanate powder is a calcined power.  
     
     
         5 . The powder according to  claim 4 , wherein the semiconducting agent is La.  
     
     
         6 . The powder according to  claim 1 , wherein the barium titanate powder is an uncalcined power.  
     
     
         7 . The powder according to  claim 6 , wherein the semiconducting agent is La.  
     
     
         8 . A process for producing a barium titanate semiconductive ceramic having an average ceramic grain size of about 0.9 μm or less, which process comprises firing a barium titanate powder having a grain size of about 0.1 μm or less, a cubic system crystal structure and a lattice constant of 4.02 angstroms or more, and a semiconducting agent in the form of solid solution, for a time and at a temperature such that the average grain size of the resulting titanate is about 0.9 μm or less.  
     
     
         9 . The process according to  claim 8 , wherein the semiconducting agent is selected from the group consisting of rare earth metal elements and transition elements.  
     
     
         10 . The process according to  claim 9 , wherein the semiconducting agent is La.  
     
     
         11 . The process according to  claim 8 , wherein the barium titanate powder is a calcined power.  
     
     
         12 . The process according to  claim 11 , wherein the semiconducting agent is La.  
     
     
         13 . The process according to  claim 8 , wherein the barium titanate powder is an uncalcined power.  
     
     
         14 . The process according to  claim 13 , wherein the semiconducting agent is La.