Preparation and characterization of BaTiO3 based dielectric ceramics

Abstract

TIle microstructure-propcrty relationship of BaTiO), Bai.,Sr,TiO)(x=O.lO, 0.15, 0.20) and SrTiOJ has been studied in this thcsis. BaTiO) and SrTiO) powders of 100nm ,,'ere used to prepJ.!'epellet shaped samples using 130-150 MPa pn:ssure. The green samples were dricd and then sintered in the tcmperature range of 1100"C to 1275°C, varying the holding time from 2 hours to 6 hours. The density, dielectric constant and loss tangent were measured using available equipment> at BUET and the Atomic Fnagy Center, Dhaka (AECD). Optical Minoscopc, Scanning Electron Microscope (SEt'..'I), Differential Scanning Calorimeter (DSC) and X-ray Diffractometer (XRD) were used to observc the microslruclmc, identify the Curie temperature and different phases to find the correlatiotl betw,eenmicrostlUcture and property ofthc sintered samples. Ninet}' five pcreent of the theoretical density has been fOlllldfor BaTiO) samples sintcrcd in the temperature range of J::!25°C-1250°C. It has been ohserycd from the microstructllTethat grain gro,vth occur, at higher temperature but porosity still remains inside the grain and in the grain bound<lrie~.rcrroelectric domain twins have be~n revealed in th~ chemically etched samples by SP/l. The frequency dependent dielectric constant and loss tangent were measurcd at room temperature for BaTiO), BahSr,TiO] and SrTiO) samples. The highest dielcctric constant was found for BaTiO] &intercdat 1100°C for 3 hours may be due to the small b'l"ainsize, Loss tangent at 1 kHz for this sample Vias , re<lsonablecompared to the other BaTiO) sample bllt at 100 kHz loss tangent ",as found maxim\lm among all the BaTiO) samples. The Sr doping was found to havc an observable ert"~C\on the dielectric propenie~. The highest dielectric constant obtained for Ba,,\Sr2TiO] at room temperature was 3000. In the case of SrTiO), the dielectric constant was found considerably lower. The loss tangent was also foul)d vcry low' for Sr1iO). The tcmperatuf~ dependent dielectric constant was measured for the BaTiOJ and Ba"Srl.,TiO) samples. Curie temperature was found at around l30°C for BaTiO). Tetragonal to cubic transformation was accompanied wilh a sharp peak for the sample sintered at I225CC for 4 hours. Curie temperature was found to decrease with an increase of Sr concentration in Bal_ ,Sr,TiO] sample sintered at 1250°C for 5 hours as expectcd.