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.
