Doped And Improved Microwave Dielectric Properties Of NdNbO₄Ceramic System

Based on the rapid development of the area of the microwave communications,peoples are paying more attention to the multi-functional materials. In this article, therare earth niobate NdNbO4was chosen as the studying object. We mainly focused onthe effect of doping and ion substitution on microwave dielectric properties ofNdNbO4. The optimal process parameters were got with the NdNbO4ceramics thatdoped and ion substituted. Based on the NdNbO4ceramics prepared by the solidphase method, niobate crystal structure, phase composition and microwave dielectricproperties were system analysed and researched.1. CaTiO3was used as addition that added in NdNbO4ceramics in order to studythe microwave dielectric properties of NdNbO4-CaTiO3system, the optimum result ofsintering temperature and the addition amount of CaTiO3were1275℃,4h and0.6wt.%. With the increase of added amount of CaTiO3, the resonance frequencytemperature coefficient of NdNbO4ceramics showed the trend of tending to zero, thedielectric constant and the relative density showed the same trending, the optimumquality factor Q×~70,000GHz (8.8GHz) of NdNbO4ceramic was obtained at thesintering temperature1275℃for4h and0.6wt%CaTiO3addition.2. According to the stoichiometry of (Nd1-xM1.5x)1.02Nb0.988O4(M=Sr, Ca, Mn, Coand x=0.0,0.01,0.02,0.03,0.04), the solid solubility limits of Sr, Ca, Mn and Co inNdNbO4were researched. The single NdNbO4phase with Sr, Ca, Mn, Co as thesubstitution ions were obtained from x=0.0to0.02, x=0.0to0.01, x=0.0to0.03andx=0.0to0.01in the order of Sr, Ca, Mn, Co. The presented second phases wereSrNb2O6, CaNb2O6, MnNb2O6and CoNb2O6. The microwave dielectric propertieswere strongly dependent on the structural characteristics. After the substitution, theunit cell volume, packing fraction and [NbO6] structure were changed. They have adirect relation with the microwave dielectric properties. The dielectric constants wererelated to the relative density and ion polarizabilities, the temperature coefficients ofthe resonant frequency τ were effected by the octahedral structures, and the qualityfactors Q×had a close relation to the packing fractions and were increased with it.3. The effects of Mn2+substitution on the microstructures and microwave dielectricproperties of NdNbO4ceramics were investigated systematically. The microwavedielectric properties of NdNbO4ceramics were strongly dependent on the Mn2+ substitution. An optimal quality factor Q×=80,000GHz was achieved for(Nd1-xMn1.5x)1.02Nb0.988O4(x=0.03)ceramics sintered at1250℃for4h.