Study On Synthesis And Structure Compatible Of New Series Complex Perovskite-type Compounds And Its Formation Regularities Its Dielectric Microwave Properties

In recent years with the development of microwave communications, especially the satellite communication, the dielectrics materials with high Q value has been studied widely. Complex perovskite compound with formula of Ba(Mg1/3Ta2/3)O3 (BMT) has been found to be a good candidate in X wave band for microwave resonators, due to its high quality factor Q and low temperature coefficient frequency τf .However ,signification problems concerning the BMT ceramic are high sintering temperature (>1650℃ for BMT ceramic prepare via solid-state reaction) ,poor sinterability (due to the presence of some second phase ,e.g.Ba4Ta2O9and BaTa2O9 etc) and long annealing time (≧100hr). For the sake of the improvement its sinterability , many scholar research the problem widely. For example ,Matdumoto etc(1986) adoption the quickly sintering craft (330℃/min) to get 98% theories density ceramics. Chen etc (1994) adoption several annealing craft to reduce the intermediate phase. But these techniques application result in:(1) Preparation complication.(2) The composition deviate stoichichemistry.(3) Harmful substance easily mixture.Although liquid synthesize method to have the BMT powder can solve this problem, but preparation of tantalite is difficult in actual application.This dissertation is to explore and develop promising tantalite material with special microwave dielectric properties. Crystal structure and formation regularities of new tantalite compounds.This thesis was divided into two parts:(1) synthesis and structure adjustment of new series of perovskite tantalite compound.(2) Microwave dielectric response of ceramic in this system was studies as function of the composition and measurement frequency.A new series of perovskite tantalite compound Ba(Mgx/12Ta2x/12Ti(12-3x)/12)O3 (2/3≦x≦4),Ba(Mgx/12Ta2x/12Zr(12-3x)/12) O3(3.667≦x≦4) were found and synthesized for the first time by solid-state reaction. With XRD analysis, a perfect equivalent is morphism between Ti and (Mg, Ta) was first investigated in the system of BaTiO3- Ba(Mg1/3Ta2/3)O3,and a new series of solid solutions formulated [Ba(Mgx/12Ta2x/12Ti(12-3x)/12)]O3 were synthesized. The unit cell parameters of Ba(Mgx/12Ta2x/12Ti(12-3x)/12)O3 decreases regularly as the content of Ti rises.The formation regularities and structure changes of compounds A(B'1/3B''2/3)O3 were investigated. According to the rules of crystallographic chemistry, it was predicted that thereexist a new series of hexiagonal tantalite compound Ba(Mgx/12Ta2x/12Ti(12-3x)/12) O3 , then Ba(Mgx/12Ta2x/12Zr(12-3x)/12) O3 , which were isostructural with Ba(Mg1/3Ta2/3)O3, were found and characterized by means of chemical analysis, SEM, optical microscope and XRD.The crystal structures of new series compound were determined with X-ray powder diffraction. The results demonstrate that Ba(Mgx/12Ta2x/12Ti(12-3x)/12) O3 crystallize in hexagonal system with space group p3ml.