Low Temperature Sintering And Properties Of BST Microwave Ceramics

Low-loss dielectric materials have attracted much attention due to its widespread applications in microwave communications,pulse energy storage field,etc.In recent years,as the rapid development of the miniaturization,integration and multifunction of electron elements,the LTCC technology has got developed.But this requires to lower the sintering temperature of dielectric ceramic.So there are more and more studies have been conducted on the low temperature sintering of dielectric ceramics.Ba4Sm9.33Ti18O54(BST)ceramic is a kind of high-? microwave dielectric ceramics which has been widely used.However,it has the high sintering temperature.And these studies are mainly focused on aspects of microwave dielectric performance.Therefore,Ba4Sm9.33Ti18O54(BST)has been chosen as the research object in this thesis.On the one hand,variations of sintering temperature,dielectric properties,structure,energy storage characteristics of by ion doping,addition of sintering additive and so on have been investigated.On the other hand,the preparation of free-sintered BST-polymer composites,dielectric and energy storage characteristics have been investigated with the introduction of polymer.(1)MoO3 doped BST microwave dielectric ceramics Ba4Sm9.33Ti18-xMoxO54+x(x=0.5,1,2,5)has been prepared by the conventional solid-state reaction method.Along with the doping amount of MoO3 increases,sintering temperature of BST gradually reduces from 1350? for x = 0 to 1200? for x = 5.Meantime,the phase transforms from tungsten bronze like BST single phase to multiphase of BST,BaMoO4 and others.And the microwave dielectric properties deteriorate.BST ceramics(x=0.5)sintered at 1325 ? exhbits good microwave dielectric properties:?=64.5,Q·f=5590 GHz,?f=-3.6 ppm/?.Meanwhile,its energy storage density of 0.066 J/cm3 is close to pure BST ceramics when the highest breakdown electric-field of 15.28 kV/mm is obtained for x=0.5.(2)Sintering aids ZnO-B2O3(ZB),CuO-B2O3(CB)can effectively reduce the BST sintering temperature from 1350 ? to about 1000 ?.But the microwave dielectric properties degrads.A small amount of the second phase Sm2Ti2O7 appears when ZB addition reaches 2%,and the Sm2Ti2O7 phase gradually increases with the increase of ZB.Optimal microwave dielectric properties of ?=63.4,Q·f=2830 GHz,?f=-8.8 ppm/? is obtained for BST ceramics with 1%ZB addition,which is sintered at 1175 0C.Howerve,the secondary phase Ba2Cu(BO3)2 only appears when the CB addition reaches 10%.BST(1%CB)ceramics sintered at 1175 ? exhibits the optimal microwave dielectric properties:?=62.7,Q·f=4270 GHz,?f=-11.1 ppm/?.Meanwhile,BST ceramics with 2%CB has the highest breakdown electric-field 18.8 kV/mm.And the largest energy storage density is 0.093 J/cm,which is 45.3%higher than that of pure BST.(3)With introduction of cyanate ester,BST/Cyanate ester composite dielectric materials has been prepared throgh immersing the BST green pellet in cyanate ester monomer.The dielectric properties of BST/Cyanate ester composites(1MHz)is?=22.2,tan8=0.016,with the breakdown electric-field of 33.7 kV/mm.So the highest energy storage density is 0.112 J/cm3,which is 74.3%higher than that of pure BST.