| Summary: | 碩士 === 義守大學 === 材料科學與工程學系 === 88 === Abstract
In order to decrease the firing temperature of Barium Titanate (BaTiO3, BT), low-melting(930℃) point Lead Iron Tungstate (Pb(Fe2/3W1/3)O3, PFW) relaxor has used as sintering aid. Lead Iron Tungstate has high dielectric constant and diffuse phase transform characteristics. Binary system in composition of xBT-(1-x)PFW (x =wt﹪) was prepared by mixed-oxides or BT-PFW mixed phases methods.
BaWO4 and BaFe12O19 phases were observed in the samples prepared by mixed-oxides or mix-phases processes when the samples were heat-treated at 500℃ for 2hours. Electrical and physical properties of BT-PFW ceramics were affected by the formation of BaWO4 and BaFe12O19 phases. Dielectric constants of BT-PFWs were in the range of 500s, since the dielectric constant of BaWO4 was as low as 8.
Two shrinkage stages were observed from the xBT-(1-x)PFW samples with x=0.2、0.5. The first shrinkage stage was considered as low-firing temperature PFW and BaWO4 phases reacting at 750℃-850℃. The second shrinkage was due to the formation of non-stoichimetric PFW liquid at 1050℃. BT particles were wetted by PFW liquid. Due to particle rearrangement, the BT-PFW samples shrunk at this temperature.
Dielectric properties of xBT-(1-x)PFW are dependent on grain size and amount of second phases BaWO4 and BaFe12O19 formed. Dielectric constant increased by the conditions of exact PFW(x=0.5) content, rapid heating rate(15℃/min), short dwelling time(30min), it reduced the contact area between BT and PFW grain and decreased the amount of second phases. Samples prepared by those conditions and sintered at 930℃, had dielectric constant of 1670. Influences from second phases and pores were not completely excluded in this research.
|
|---|
