Microstructure And PTC Mechanism Of Barium Titanate Based PTC Ceramics

With the rapid development of science and technology, the PTC materials availablenowadays bacome more and more unsatisfied for the rigid requires of the people. Themicrostructure of the material determines its performance. So the study on microstructureof PTC material and PTC mechanism become the key to ceramic material development. Atpresent, there are not comparatively detailed reports carried on to study the microstructureof the PTC ceramics. This subject is launched for the deficiencies of this aspect, make themicrostructure and mechanism the focal point of the work. At first, the PTC powder wasprepared by citrate sol-gel method, then the PTC ceramics was prepared on this base,during these procedures the PTC powder and ceramics were studied overall by means ofXRD , SEM , TEM , EDS ,etc.The citrate sol-gel method was used in the preparation of donor doped BaTiO3 powder,and the pH value in solution; the water content; heat treatment temperature, etc. wereanalysed. Result indicate that in the sol form stage the suitable pH in 6.5-7.5, the range ofwater R([H₂O][Ba²⁺]) in 70-80, the suitable heat treatment temperature is 600℃,heattreatment time is 2h. Finally the powder abtained is in forms of cellular foam, and can beseparated easily into even size, the first particle size is about 30nm.In the course of ceramics preparation, when the mixing amount of Y and Mn is 0.7mol% and 0.06mol%, the ceramics, under room temperature ρis 147Ω·cm, ratio oflg(R_max/R_min) reach to 5, was abtained. At the same time, we found that with the increase ofdonor content the room temperature resistance changes in "U"shape, and Mn increases theresistance jumping property. By the study on ceramics prepared with large quantity ofdonor, we found that the semiconducting is a process controlled by energetics while thatthe PTC forming is controlled by dynamics, the potential barrier can be adjusted by thecontrol of sintering schedule.By the studies on microstructure of the PTC ceramics, we found that the best size ofcrystalline grain is about 15-20μm; Ca can not solute continuously in the crystal, rightamount of Ca can diminish and even the crystal size; the impurity elements tend tosegregate on the grain boundary. In addition we found that the grain body and domainappereace are different with the different donors, the domain appereace of Y dopedsamples is in shape of fish bone while the Sr doped in shape of orthogonal frame, ceramicswith orthogonal frame domains is better in resistence jumping property. Through the EDSanalysis we found there are regularitys in the element distributing, the lagest difference ofelement content in grain body and grain boundary is oxygen, so we can conclude thatoxygen plays a big role in potential barrier.