| Low temperature co-fired ceramics (LTCC) technology which widely applied incommunication system has been an important approach to actualize miniaturization,low-cost and modulization of various components. Microwave dielectric ceramicshave been a hot research topic for LTCC. The development and application of middleand high permittivity LTCC materials are much slowly than low permittivity LTCCmaterials, especially the permittivity between 45 and 70. The difficulties are not onlyto reduce the sintering temperature, but also to obtain good dielectric properties andmeet LTCC application (stable slurry and co-fired with Ag electrode).For the purpose to prepare middle permittivity (εr=45-70) LTCC microwavedielectric materials, low temperature sintering, ions substitution and LTCC applicationof Ba3Ti4Nb4O21(BTN) ceramics were studied in this dissertation. The researchoutlines and conclusions are as follows:(1) To reduce the sintering temperature and improve the dielectricproperties of BTN ceramics, the effects of B2O3, CuO, MnCO3-CuO and ZBSadditives on the sintering behavior, microstructures and microwave dielectricproperties of BTN ceramics has been investigated. The research indicated thatadditives became liquid phase during sintering which promoted sinterability bysolution-reprecipitation mechanism. The effect of reducing the sintering temperatureof BTN ceramics with single B2O3 or CuO additive was common. It was found1wt%B2O3 and 1wt%CuO lowered the sintering temperature of BTN ceramics from1280℃to 1100℃and 975℃, respectively. The calcined MnCO3-CuO (MC) additivecan effectively decrease the loss and keep the effect of reducing temperature by CuO.BTN ceramics with 1wt%MC and 2wt%ZBS additives sintered at 900℃for 2hshowed good Q×f values (Q×f=13500GHz) which excelled the earlier report(Q×f=3000GHz). However, theτf was 42×10-6/℃which could not meet therequirement of LTCC application.(2) In order to decrease theτf of BTN ceramics, the effects of A and B site ions substitution on microwave dielectric properties of BTN ceramics has beenstudied. MgTi2O5, Ti1/2Mg1/6Nb1/3O2, CaNb2O6 and Ca3Nb2Ti3O14 phases were foundwhen Ba2+ substituted by Mg2+ and Ca2+ which worsen the dielectric properties. Itcould form complete solid solution without the second phase when Ba2+ substitutedby Sr2+. Theεr andτf increased but the cell unit volume decreased with the increasingof Sr2+ substitution. The B site ions (Ti4+) substituted by Zr4+, Sn4+, (Zn1/3Nb2/3)4+ and(Fe1/2Nb1/2)4+. All of them could form complete solid solutions. The substitution of Bsite ions conduced to inclining oxygen octahedra, which effectively decreased theτf ofBTN ceramics. The dielectric properties of samples was optimal when 50mol% ofTi4+ substituted by (Zn1/3Nb2/3)4+. The Q×f values was 15700GHz and theτf was20×10-6/℃. The other substitutions more or less decreased the Q×f values of BTNceramics.(3) Based on low temperature sintering and substitution, slurrycharacteristic and co-firing with silver electrode of Ba3Ti2(Zn1/3Nb2/3)2Nb4O21ceramics with MC and ZBS were studied systematically, and a type of lowtemperature firing microwave dielectric ceramics with excellent properties andapplication values was obtained. Ba3Ti2(Zn1/3Nb2/3)2Nb4O21 ceramics with1wt%MC and 1wt%ZBS sintered at 900℃for 2h exhibited excellent dielectricproperties ofεr, Q×f=14800GHz,τf=6×10-6/℃. The powders could form stableaqueous slurry and the tapes shaped by tape-casting had smooth surface and uniformstructure. The interface between the silver electrode and ceramic was compactnessand no reaction occurred. It was a promising middle permittivity LTCC microwavedielectric materials. |
