| Nowdays,the operating frequency ranges of microwave wireless communications are expanding.As a result,microwave dielectric materials with a low dielectric constant(?r),a high quality factor(Qxf),and a near-zero temperature coefficient of resonant frequency(?f)are urgently required.In addition,further improvements have been made in the miniaturization,lightening,multifunction and highly reliable of microwave devices.Low temperature co-fired ceramic(LTCC)technology offers significant benefits over other established packaging technologies for high-stability,low-cost and miniaturization for the microwave devices.LTCC requires the microwave dielectric ceramics with high performance and low sintering temperature,which is lower than the melting point of Ag(960 ?).However,most microwave dielectric materials(with low a low ?r,and a high Qxf)used for high frequency field suffer a high sintering temperature(above 1200 ?)as well as a little large ?f,which limit their use in LTCC application.Therefore,the LTCC materials must have high performance(low ?r,high Q,near-zero ?f)and low sintering temperature,which is lower than the melting point of Ag(960 ?).Therefore,the development of LTCC materials with high performance has attracted much attention in recent years.In recent years,a new microwave dielectric material of Mg2TiO4 with a low dielectric constant has been reported.Its low cost even brought much more attention.However,its higher sintering temperature and large ?f limit its further application.In addition,it also has the disadvantage of the formation of second phase MgTi2O5 during the process,which would cause deterioration in microwave dielectric properties.The present study was undertaken to understand the effects of partial Zn substitution for Mg and Sn substitution for Ti on the microwave dielectric properties of(Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4(MZTS)ceramics.In order to lower its sintering temperature,an amount of LiF was added to the MZTS ceramics.The if value of MZTS ceramics was compensated by an amount(Ca0.8Sr0.2)TiO3 addition.With multicomponent sintering agents addition,the sintering temperature of 0.9(Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4-0.1(Ca0.8Sr0.2)TiO3 composite ceramics can be lowered to 950 ?.A novel series of low ?r microwave dielectric materials with intrinsically lower sintering temperature has been explored.The microwave dielectric properties of Ca5A4(VO4)O6(A=Mg?Zn?Co)ceramics with cubic garnet structure have been investigated.The ?fvalues of Ca5A4(VO4)O6 ceramics were compensated by an amount(Ca0.8Sr0.2)TiO3 addition.The principal experiment results were shown as follows:(1)The(Mg0.95Zn0.05)2(Ti0.8SnO.2)O4(MZTS)ceramics were synthesed by the solid-state reaction method with various sintering temperatures.With partial Zn substitution for Mg and Sn substitution for Ti in Mg2TiO4 ceramic,the secondary phase MgTi2O5 was suppressed,and the sintering temperature can be lowered.The MZTS ceramic sintered at 1325 ? for 5 h had ?r=13.1,Qxf=131 170 GHz(10GHz),?f=-56 ppm/?.The sinterability and microwave dielectric properties of LiF-added MZTS ceramics were investigated.An amount of LiF addition can effectively lower the sintering temperature of MZTS from 1325 ? to 1150 ? due to the liquid phase effect and induce no apparent degradation of the microwave dielectric properties.The MZTS-3.0 wt%LiF ceramic sintered at 1150 0C for 5 h showed s,=13.1,Qxf=119 310 GHz(10.1 GHz),?f=-60 ppm/?.(2)The sinterability,phase composition,microstructure,and microwave dielectric properties of 0.9(Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4-0.1(Ca0.8Sr0.2)TiO3(MZTS-CST)were investigated.The MZTS-CST ceramics sintered at 1325 ? exhibited ?r =18.2,Qxf=49120 GHz(8.1 GHz),?f=15 ppm/?.The effects of LiF-Fe2O3-V2O5(LFV)addition on the sinterability,phase composition,microstructure,and microwave dielectric properties of MZTS-CST were investigated.Eutectic liquid phases(CaMg)V2O6 and 0.12CaF2/0.28MgF2/0.6LiF were developed,which lowered the sintering temperature of MZTS-CST ceramics from 1325 ? to 950 ? due to the reactive liquid-phase sintering.Secondary phase CasMg4(VO4)6 as well as residual liquid phase affected the microwave dielectric properties of MZTS-CST composite ceramics.Typically,the MZTS-CST-5.3wt%LFV composite ceramics sintered at 950 ? showed excellent microwave dielectric properties:?r =16.3,Qxf =30 790 GHz(8.3 GHz),?f=-10 ppm/?(3)The sintering characteristics,microstructure and microwave dielectric properties of the Ca5A4(VO4)6(A=Mg?Zn?Co)ceramics were investigated systematically for the first time.We also try to discussed the relation between the packing fraction and sintering temperature of Ca5A4(VO4)6 cermics.This results provide a potential material for microwave electronic components working at higher frequency.A series of new low dielectric constant microwave dielectric materials with intrinsically lower sintering temperature were obtained.The Ca5Mg4(VO4)6 ceramic sintered at 800 0C for 5 h showed:?r=9.2,Qxf =53,300 GHz(at 10.6 GHz),?f =-83 ppm/?.The Ca5Zn4(VO4)6 ceramic sintered at 725 0C for 5 h exhibited:?r=11.7,Qxf =49,400 GHz(at 9.7 GHz),?f=-83 ppm/?,which also showed wide sintering range?The Ca5Co4(VO4)6 ceramic sintered at 900 ? for 5 h had ?r =10.1,?f=-63 ppm/?,Qxf =95,200 GHz(at 10.6 GHz).Although Ca5A4(VO4)6 ceramics show promising microwave dielectric properties(low ?r and high Q)combined with inherently lower sintering temperature,however the large negative ?f values limit their further application.Therefore,their near-zero ?f values are expected for the practical application.(4)The ?f of Ca5A4(VO4)6 ceramics was adjusted by doping(Ca0.8Sr0.2)TiO3,which has large positive ?f.The(1-x)Ca5A4(VO4)6-x(Ca0.8Sr0.2)TiO3 composite ceramics were prepared by the conventional solid-state method,respectively.CasA4(VO4)6 reacted with(Ca0.8Sr0.2)TiO3 when(1-x)Ca5A4(VO4)6-x(Ca0.8Sr0.2)TiO3 composite ceramics are tried to be prepared and the phase composition changed with composition x.The ?f of the ceramics changed from negative to positive with the increase composition x.The 0.35Ca5Mg4(VO4)6-0.65(Ca0.8Sr0.2)TiO3 composite ceramics sintered at 950 ? for 5 h showed:?r=12.4,Qxf =17,800 GHz(at 9.4 GHz),?f =-8 ppm/?.The 0.3Ca5Zn4(VO4)6-0.7(Ca0.8Sr0.2)TiO3 composite ceramics sintered at 875 0C for 5 h exhibited:?r =13.5,Qxf =12,800 GHz(at 8.9 GHz),?f =3 ppm/?.The 0.3Ca5Co4(VO4)6-0.7(Ca0.sSr0.2)TiO3 composite ceramics sintered at 900 ? for 5 h had?r = 13.4??f =7 ppm/??Qxf =22,500 GHz(at 9.0 GHz). |
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