Microstructures and PTC-Mechanism in Pb TiO_3-TiO_2 PTC Ceramics for High Temperature Applications

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The purpose of the present studies is to establish the preparation techniques of PbTiO_3-TiO_2 ceramics as PTC thermistors, and to clarify the PTCR mechanisms. The obtained results are summarized as follows ;1. Optimum conditions of preparing techniques are established. Optimum compositions are PbTiO_3-(30-80)mol%TiO_2, and which are fired at 975ﾟC-1025ﾟC for 2 hr in Ar atmosphere.2. Heating temperatures of the thermistors can be controlled by lowering the Curie temperature. of the system with the addition-of SrTiO_3. For an example, the Curie temperatures of the samples with 30%SrTiO_3 addition, is around 350ﾟC.3. The addition of oxides of transition metals increased the PTCR properties, and furthermore improved their stabilities.4. Present studies find that the PTCR properties are originated not only from the interfaces of ferroelectric PbTiO_3 grains, but also interfaces of PbTiO_3 and TiO_2 grains. This results are obtained by the direct - observations of temperature resistivities properties on the samples where Pt electrodes are connected with the coarse grains of PbTiO_3 and TiO_2.The atmosphere for resistivity-temperature measurement affects PTCR properties, which are disappeared with vacuum atmosphere. Then the oxygen plays important role in originating the PITCR properties.