Investigation On Structure And Dielectric Properties Of CAS Glass/SBN Ceramics

SBN(Sr_1-xBa_xNb₂O₆,x=0.25-0.75) with tetragonal tungsten-bronze structure are particular interested because of their excellent ferroelectric, piezoelectric, pyroelectric and nonlinear optical properties. The relations between sinter temperature, structure and dielectric properties of SBN ceramics were investigated. The results show that SBN40,SBN50 and SBN60 were easier to generate single-phase with tetragonal tungsten-bronze structure, while SBN25 had a complex-phase of tetragonal tungsten-bronze and prochlore. Dense temperature of SBN40 and SBN50 is about 1300 oC ,lower than SBN60's 1350 oC ,and to SBN25 it was more than 1350 oC. Density and lattice parameter increased gradually as Ba content increased. The permittivity decreased with the increasing of testing frequency. Sinter temperature show obvious influence on phase composition, crystal structure and dielectric properties of SBN ceramics. It tended to be tungsten-bronze phase and had a high permittivity with a high sintering temperature. SBN ceramics had a behavior of dielectric relaxation, and its curie point increased from room-temperature to around 120oC with Ba content increased. Ferroelectric glass-ceramic SBN50 was synthesized by sintering process. Different samples sintered at different heat treating regime had led to different phases, F1-50 generated SiO2,α-CaSiO₃ and parawollastonite,F2-50-F40-50 generated CaNb2O6 and SBN,F5-50 generated single-phase SBN. The dense temperature decreased first ,and then increased with the addition of SBN. An obvious diffuse dielectric peak was observed at around 85oC for the sample F5-50, which was sintered at 900 oC for 2h and 1250 oC for 2h. And the temperature corresponding to the maximum of dielectric constant shifted to higher temperature with increasing frequency, showing a typical relaxor ferroelectric phase transition. The glass-ceramic SBN40 variation of structure and dielectric properties were further investigated. The major phase varied from SiO2 to CaNb2O6,and then to SBN with the addition of SBN, and at last it changed to single-phase SBN when the content of SBN reached 90wt%.As sintering temperature increased, the reflection of CAS and SBN was greatly promoted. An obvious diffuse dielectric peak was observed at around 73oC for the sample F5-40, which was sintered at 900 oC for 2h and 1250 oC for 2h. And the temperature corresponding to the maximum of dielectric constant shifted to higher temperature with increasing frequency, showing a typical relaxor ferroelectric phase transition.