Synthesis Of Znnb₂o₆ And Znta₂o₆ Ceramic Powders

In recent years, the binary niobate such as AB2O6 (where A=Ca, Mg, Zn, Co, Ni, Cu, Mn and B=Nb, Ta) have attracted considerable attention for the excellent dielectric properties such as low loss and high dielectric constant and good crystal nonlinear effects, electro-optic effects and refraction effects. Thus they are going to be the promising candidates for application in microwave devices, laser frequency doubling devices and electro optic phase modulator. Among these compounds, ZnTa2O6 and ZnNb2O6 have excellent dielectric properties. ZnTa2O6:Q×f=65200 GHz,εr= 37.6å'ŒÏ„f= 9 ppm/°C. ZnNb2O6:Q×f=87300 GHz,εr=25 and tf=56 ppm/°C. To our knowledge, there has been no known report about preparing of ZnTa2O6 powders by molten salt method and ZnNb2O6 powders by hydrothermal method. The research in this paper is on top of the academic.In this study, ZnTa2O6 powders are prepared by molten salt method and ZnNb2O6 powders are prepared by hydrothermal method. The process and the condition of two methods are studied in detail. The influence on the powders crystallization and morphologies with different processing conditions is discussed in emphasis. The products are characterized by XRD, SEM,TEM,HRTEM, EDS.Zinc'tantalate powders have been successfully synthesized via molten salt method by selecting solvent system. After that, the phase formation and morphology of the obtained ZnTa2O6 powders under different reaction conditions including temperature, molar ratio of solvent and raw materials of zinc have been discussed. The results are listed as follows.(1) Three kinds of solvent system have been selected and investigated in the pre-part of the experiment, including KCl-NaCl, KCl-NaCl-ZnCl2, and MCl-ZnCl2. The KCl-ZnCl2 system has been determined to be a right solvent for the formation of zinc tantalate. ZnTa2O6 powders have been successfully synthesized via molten salt method at temperature of 700℃-800℃using Ta2O5 and Zn(NO3)2·6H2O as starting materials and a mixture of KCl and ZnCl2 as a solvent. (2) The optimum conditions for the synthesis of ZnTa2O6 powders under the same solvent which has been discussed in above have been also discussed by changing different reaction conditions including temperature, molar ratio of solvent and raw materials. The results showed that fine ZnTa2O6 powders can be obtained by using a mixture of KCl and ZnCl2 (molar ratio of KCl to ZnCl2≤0.1:1) as a solvent and calcining at 700℃for 3h. Zn(NO3)2·6H2O has been considered to be the fine starting material by comparing with ZnO and Zn(OH)2. In general, the particles of the obtained ZnTa2O6 powders are agglomerated and irregular in shape with a mean particle size of 700nm.ZnNb2O6 nanopowders have been successfully synthesized via hydrothermal method. The effects of synthesis temperature, reaction time, solvent, pH and mineralization on phase composition and particle morphology have been investigated in this paper. The products have been characterised by XRD, SEM, TEM, HRTEM and EDS techniques. The results are listed as follows.(1) ZnNb2O6 nanopowders could not be obtained by using water as solvent via hydrothermal method under different conditions including raw materials, pH and mineralization.(2) ZnNb2O6 nanopowders have been successfully synthesized by using cyclohexane as solvent. The particle size of ZnNb2O6 powders is 50-200 nm.(3) The effects of synthesis temperature, reaction time, solvent and mineralization on powders have been investigated. Cyclohexane has been considered to be the fine solvent by comparing with TMAH and hexamethylene diamine in this paper. ZnNb2O6 nanopowders could be synthesized when mineralization is not being used. The crystal ZnNb2O6 could be successfully obtained at a hydrothermal temperature of 190℃or above. The phase composition of product has no obvious change as the temperature increased from 190℃to 200℃. The reaction time has no effect on phase composition of product powders, so prolonging the holding time has no positive effect on the phase composition of ZnNb2O6 in this study. In a word, ZnNb2O6 nanopowders could be successfully synthesized by using Nb2O5 and Zn(NO3)2·6H2O as raw materials and cyclohexane as solvent at a hydrothermal temperature of 190℃or above with different reaction time (from 10min to 6h) in the present study. The primary particles have good crystal structure and broad particle size distribution of 50-200 nm. The large particles are found to be agglomerates of primary particles.