攙雜不同附加物下鈦酸鉛鋇正溫度係數電阻之晶界受體態的探討

Abstract

本論文研究的重點在於探討攙雜不同附加物下, 其對於以商業粉末製作而 成的鈦酸鉛鋇正溫度係數電阻(PTCR)造成哪些電性上的影響. 這些附加 物(錳,硼,鈣)一般被用來當做燒結助劑或是受體(Acceptor)態的的功能 . 其中, 我們發現添加氮化硼具有防止鉛揮發的功能而且對電性亦具安定 化的效果. 另外, 這□也提及不同的添加物各自會產生相應數量的表面 態 (surface states), 這些表面態的來源包括錳離子的析出行為, 硼存 在於晶界上所造成的氧吸附反應, 鈣取代鈦位置的作用, 甚至天生本質就 有的陽離子缺陷. 由一些實驗証明也提供這些表面態可能共存於晶界附 近, 而且擁有各自的表面能階. 在此, 我們利用這些不同型式的表面態可 能在能帶中"共存"的觀念來計算電阻曲線, 發現所得與實驗結果產生相當 滿意的吻合. 我們的實驗結果是以Heywang-Jonker模式為基礎來做各種電 性的分析而且也已証明在一系列的樣本中, 若就晶界受體態在能帶中的能 量分佈及型式予以分類驗明, Heywang能障的假設是一相當合理的方法. The electrical properties of positive temperature coeffici- ent of resistance ceramics of composition (Ba,Pb,La)TiO3 prepar- ed from commercial powders doped with different additives were studied. These additives (Mn,BN,Ca) were commonly either used as sintering aids or served as the acceptor's function. Among them, it was found that BN exhibited a pronounced effect in preventing the volatilization of lead and stabilized the electrical- property performance. It was also proposed here that different additives might have generated the corresponding number of possible surface states, such as, the segregation behavior of Mn ions (3d transition metal), oxygen adsorption reaction resulting from the existence of B at the grain boundary, the action of Ca replacing the Ti sites, even natural intrinsic defects. And, in general, some experimental derivations were also offered that majority of the surface states, which possessed their individual surface energy level, were possibly coexisted onto the grain surface. Utilizing the concept of the coexistence of different types of surface states in energy band, a satisfactory point-to -point agreement was obtained between the measured result and calculated values for the resistivty curve.......