Research On Shrinkage Control Mechanism And Low-Temperature Sintering Of BaAl₂Si₂O₈Substrate For High Frequency

BaAl₂Si₂O₈-based （BAS） ceramics were prepared by conventional solid-state reaction.Shrinkage control mechanism and low-temperature sintering technology ofBaAl₂Si₂O₈-based substrate were studied。Using ethanol as milling dispersant BaCO₃, Al₂O₃and SiO₂raw material can not bemixed sufficiently. The sintered ceramic contained a large number of pores caused byresidual BaCO₃in calcined powder, and the shrinkage was negative. Using deionized wateras the milling dispersant, the raw materials can be mixed sufficiently. Dense ceramics withlarge shrinkage can be synthesized. Using Al₂O₃material （YFA-12G Al₂O₃） with smallerparticle size, small shrinkage can be obtained. Using Al₂O₃material （SINOPHARM Al₂O₃）containing inhomogeneous composition with low activity, ceramics with moderateshrinkage can be obtained. Using raw materials （YFA-13G Al₂O₃） with uniform andmoderate particle size, dense BaAl₂Si₂O₈ceramics with large shrinkage and bestmicrowave dielectric properties （ε_r=6.51, Q·f=49614GHz, Ï„_f=-51.8ppm/oC） can beobtained.When adding a large amount of Li₂CO₃（4¹0wt%） to BaAl₂Si₂O₈, BaAl₂Si₂O₈convened completely to monoclinic phase from hexagonal phase. Nevertheless a smallamount of impurity appeared. Lithium element and BaAl₂Si₂O₈formed a solid solution. Asthe content of Li₂CO₃increased, melting point and sintering temperature ofBaAl₂Si₂O₈-based ceramics decreased. Q·f value of the ceramics was also reduced. Theceramics sintered at1100oC with10wt%Li₂CO₃showed good microwave properties: ε_r=6.37，Q·f=13122GHz，τ_f=-60.7ppm/oC.TiO₂was added to low-temperature sintering BaAl₂Si₂O₈-based ceramics to adjust thetemperature coefficient of resonate frequency （τ_f）. There was no TiO₂phase inBaAl₂Si₂O₈-based ceramics. TiO₂and BaAl₂Si₂O₈formed a solid solution. TiO₂canpromote grain growth and the sintering temperature decreased slightly. The Q·f value of theceramics increased a little. As the content of TiO₂increased, the permittivity of theceramics increased. With the increase of the TiO₂addition amount, the Q·f value increase firstly and then have the trend of decrease, and the optimal TiO₂addition amount is12wt%.With the increase of TiO₂addition amount, the Ï„_fvalue moved toward positive valueapproaching zero value. When the TiO₂addition amount was12wt%, the Ï„_fvalue wasclosest to zero and the optimal microwave dielectric property: ε_r=7.68，Q·f=15605GHz，τ_f=-18.5ppm/oC was obtained.