正溫係數電阻器（Positive temperature coefficient of resistivity, PTCR）材料已經成為很重要的零件，而由鈦酸鋇化合物是其中最重要的材料。鈦酸鋇是鈣鈦礦結構，在常溫下為正方晶系（tetragonal）鐵電材料。當添加微量的施體時，鈦酸鋇會半導化，且有正溫係數電阻效應，半導化鈦酸鋇陶瓷會受到施體添加量以及製程的影響。

　　本研究主要討論在添加不同濃度的鑭（0.2～0.4at%），在不同的冷卻速率下，觀察室溫電阻的變化和正溫係數電阻行為的變化，直流電阻率隨溫度變化的量測從室溫到280℃，且利用交流阻抗量測各個試片在不同溫度的阻抗以了解其晶體各個部份的電性隨溫度的變化。此外，利用掃描式電子顯微鏡（SEM）觀察各個試片的微結構。在此研究中，可發現當添加量為0.3at%時，電阻值最小，且有較好的PTCR效應；而當在較慢的冷卻速率下，PTCR的躍升值會增加，且躍升的斜率會較陡峭。藉由阻抗分析可將晶粒和晶界電阻分開，顯示出PTCR效應主要來源是晶界。在SEM照片所顯示出冷卻速率對微結構沒有很大影響，晶粒大小約略相同。

　　The Positive temperature coefficient of resistivity (PTCR) materials have become very important components, and among these materials barium titanate (BaTiO3) compounds are the most important group. BaTiO3 is a perovskite structure with ferroelectric properties at room temperature. Small amounts of donor doping in BaTiO3 cause semiconductivity and PTCR effect in this material. The PTCR effect of semiconducting BaTiO3 ceramics can be remarkably influenced by both donor dopants and ceramic processing.

　　The effects of La dopant （0.2～0.4at%）and different cooling rates on the room resistance and the PTCR effect were investigated in this paper. DC resistivity measurements were carried out as a function of temperature from the room temperature up to 280℃ and data of ac impedance was measured at different temperatures to know the electricity of the individual part of the polycrystalline BaTiO3. Besides, Scanning electron microscope (SEM) was employed to study the microstructures. In this paper, we found that the resistance reached minimum when dopant concentration reached 0.3at%, and the specimen brought about the better PTCR effect, resulting in an increase in the steepness of the resistivity-temperature plots in the region of the transition from low to high resistance. We can separate the grain and the grain boundary resistance by impedance analyses and we found that the origin of the PTCR effect was the grain boundary resistance. It was found that the cooling rates didn’t have significant influence on the microstructure such as grain sizes.

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