Some Results on Microanalysis of PTCR Materials Based on (Ba-Pb)(La)TiO_3 Solid Solution
Huang Zhongzang (Shanghai Institute of Ceramics,Academia Sinica)Hsich K.C.(Materials Res.Lab.,Univ.of Illinois,USA)Payne D.A.(Dept.of Ceramic Eng.,Univ.of Illinois,USA)
PTCR materials based on(Ba-Pb)(La)TiO_3 solid solution were preparedby using the mixed oxide method,and microanalyses,including SEM,SIMS,AES,TEM and EDAX,were carried out on the samples with phase transitiontemperature of 300℃.The results obtained could coincide with each other andbe useful to explain the phenomena presented in this work.The microstructure of the material is an important factor to determine thePTCR performance of the final samples.In this system,the additives,Al_2O_3,SiO_2 and excess BaO,could improve the microstructural development and enhan-ce the PTCR effect of the samples.Al~(3+),Si~(4+) and Ba~(2+) ions exhibit fairly highcontents near the grain boundary,however,the distribution of La~(3+) ions exhibita tendency of gradual increase from the grain boundary to the interior of thegrain.Mn~(2+) ions apparently segregate at the grain boundary and acts as an ac-ceptor.The results obtained in this experiment,i.e.a considerable high PTCReffect existing in the samples with excess BaO in their compositions and the in-homogeneous distributions of some such ions,could not show that there is theexsistance of Ba~(2+) vacancies-rich layer along the grain boundary in the PTCRmaterials.