Research On Microwave Dielectic Properties And Low Temperature Sintering Of CaO-SrO-Li₂O-Sm₂O₃-TiO₂ Ceramics

(Ca_1-xSr_x)_1-y(Li_1/2Sm_1/2)_yTiO₃(CSLST-y-x) microwave dielectric ceramics were prepared by solid sate reaction technique in this dissertation. Using low melting point glass and oxide as sintering additives, the effects of different sintering aids on sintering characteristics, phase compositions, microstructures and dielectric properties of microwave ceramics were also studied. The low-temperature sintering properties and mechanisms of CSLST-y-x microwave dielectric ceramics were researched.The results show that a pure orthorhombic perovskite structure forms within the y range of 0.7-0.8 mol and x range of 0-1/10 mol; the best sintering temperatures of CSLST-y-x are 1 250, 1 200 and 1 175℃in the y range of 0.7, 0.75 and 0.8, respectively; the sintering temperatures of the Sr²⁺ modified the ceramics are efficiently decreased by nearly 200℃; the dielectric constantεr, the product of quality factor and resonance frequency (Qf ) value and the temperature coefficient of resonant frequencyÏ„f decrease with the increasing of y content; the CSLST-0.7-1/16 ceramic sintered at 1 250℃for 5 h exhibits excellent microwave dielectric properties:εr= 118.3, Qf=2 989 GHz,Ï„f= 47.49 ppm/℃; the CSLST-0.75-1/16 ceramic sintered at 1 200℃for 5 h exhibits excellent microwave dielectric properties:εr=97.2, Qf=2490 GHz,Ï„f=14.74 ppm/℃.The low-temperature sintering of CSLST-y-1/16 microwave dielectric ceramics were researched by using Li2O-B2O3-SiO2-CaO-Al2O3(LBSCA),B2O3-CuO (BC) and B2O3-CuO-Li₂CO₃ (BCL) as sintering additives. The results indicate that the major phase of additives-doped CSLST-y-1/16 ceramics is orthorhombic perovskite and dielectric properties of microwave ceramics are decreased. (1) The sintering temperature of CSLST-0.75-1/16 ceramics is reduced by 300℃using 5-15 wt% LBSCA as sintering additives. The sample of CSLST-0.75-1/16 with 5.0 wt% LBSCA sintered at 1 000℃for 5 h has excellent dielectric properties:εr = 84.7,Qf = 2 446 GHz,Ï„f = -12.48 ppm/℃. (2) 2-14 wt% BC additives can effectively decrease the sintering temperature of CSLST-0.75-1/16 from 1 200℃to 1 000℃. The sample of CSLST-0.75-1/16 with 5 wt% BC sintered at 1 000℃for 5 h still has excellent dielectric properties:εr = 80.3, Qf = 1 380 GHz,Ï„f = -32.89 ppm/℃. (3) BCL additives can effectively decrease the sintering temperature of CSLST-0.7-1/16 from 1 250℃to 1 000℃, The sample of CSLST-0.7-1/16 with 5 wt% BC and 0.5 wt% Li₂CO₃ can be sintered at 900℃for 5 h and still show excellent dielectric performance:εr = 84.7, Qf = 1 929 GHz,Ï„f = 28.76 ppm/℃.A series of low-temprature sintering microwave dielectric ceramics with excellent dielectric properties would be achieved, based on the research of the microwave dielectric properties and the low-temperature sintering of CSLST-y-x ceramics.