半導性チタン酸バリウム厚膜における正の抵抗温度特性

抄録

A large positive temperature coefficient of resistivity (PTCR) in thick films of Sb-doped barium titanate was observed by treating the films with In-Hg alloy. The thick film was deposited on an alumina plate which was quietly laid in an alcoholic dispersion liquid of the semiconducting fine powder till the alcohol of dispersion medium volatized thoroughly in a dry oven. Then, the film was fired at 1280°C for 25min in air. The film thickness was controled by the weight of the powder in the dispersion liquid to give the sheet density about 0.025g/cm². Its thickness was about 50μm and its color became light grayish blue. After In-Hg alloy was rubbed smoothly as the conduction treatment on the film surface the plate was heated at 1050°C for about 25min in air. This idea to obtain good conduction properties came from the investigation of composite ceramics with texture modified.
The sheet resistivity of the film as prepared was larger than 10¹²ohm/_??_ at room temperature, while by the In-Hg treatment its resistivity became extremely small of the order of 10⁷ohm/_??_ and the PTCR effect over two orders of magnitude appeared above the Curie temperature. It should be noted that as the film thickness is 50μm the sheet resistivity of 10¹²ohm/_??_ corresponds to the apparent volume resistivity of 5×10⁹ohm⋅cm. This apparent high resistivity seems to be attributed to cracks, only around which In-Hg alloy remaining after the treatment was observed under an optical microscope. The current-voltagecharacteristic of the thick film treated with In-Hg was quite like to that of semiconducting barium titanate ceramics, while on the film as deposited a large voltage dependence of resistivity was observed.