The Research Of Magnesium Niobate Chramics By Polymeric Precursor Method

Magnesium niobate (Mg₄Nb₂O₉) microwave medium ceramics were prepared by the polymeric precursor method. Nb-citric acid complex was used as a raw material instead of metal alkoxide in the Sol-Gel method. Mg-Nb precursor sol can be prepared in an aqueous solution, and the problem of using the metal alkoxide such as hydrolyzation, unstable and high price can be solved by using this method.The metal-citric acid complexes were prepared using Nb₂O₅ as raw materials, citric acid as chelating agents. The Mg-Nb precursor gels were prepared by citric acid technique and EDTA technique. The powders prepared by two techniques were characterized by XRD.The results showed the EDTA technique was not suit for preparing the precursor gels.So, we used acid technique at last. At the same time, the principle of citric acid technique analysed. The Mg-Nb polymeric gels were prepared using Nb-citric acid complex in an aqueous solution with citric acid (CA) as chelating agent and ethylene glycol (EG) as esterification agent by polymeric precursor method. The thermal decomposition of the Mg-Nb precursor gels was studied by TG-DTA and the ceramic powders annealed at different temperatures were characterized by XRD and Fourier transform infrared. Homogeneous Mg-Nb precursor solution and gel with no precipitate can be achieved at pH =8 with the molar ratio of CA : metal cations=12:1 and CA:EG = 1:2.The ceramic powders can be obtained by calcined the Mg-Nb precursor gels at 800℃for 2h.Then, the ceramic powders will be molded and sintered and the ceramics subject to surface treating. The morphology and phase composition of the ceramic powders annealed at different temperatures were characterized by transmission electronic microscope (TEM), FT-IR and XRD. The ceramic annealed at different temperatures were observed by scanning electronic microscope (SEM).The ceramic sintered at 1300℃for 6h was characterized by E8363A PNA Series Network Analyzer Agilent .The resalts revealed that there was the average size of the powders was 40⁷0nm.The dielectric constant was 11.689 and the Q·f was171860.