Study On The Modification And Tape Casting Technology Of Li₃MgNbO₆ Microwave Dielectric Ceramics

The rock-salt structured ceramic of Li₃Mg₂NbO₆ sintered at 1250°C has excellent microwave dielectric properties.However,due to its high sintering temperature,the ceramic can not be applied in low temperature co-fired ceramic?LTCC?.In this paper,the sintering temperature of Li₃Mg₂NbO₆ is reduced by adding low-melting-point compounds CuO or BaCu?B₂O₅?.Since BaCu?B₂O₅?-doped Li₃Mg₂NbO₆ not merely satisfies the sintering temperature requirements of LTCC but also has good microwave dielectric properties.As is one of the most important processes of LTCC,exploring the Taping casting process of BaCu?B₂O₅?-doped Li₃Mg₂NbO₆ is of great significance in application.Finally,because of the charging effect,it is difficult in obtaining the clear morphology of the high-resistivity Li₃Mg₂NbO₆ ceramic by Scanning Electron Microscopy?SEM?.Therefore,in order to improve the quality of the SEM image,the relationship between the quality of the SEM image and the test methods have been investigated.The main research works are as follows:?1?The effects of CuO,BaCu?B₂O₅?on the sintering temperature and microwave performance of Li₃Mg₂NbO₆ have been studied by the traditional solid-phase method.Both of the low melting point compounds can remarkably reduce the sintering temperature of Li₃Mg₂NbO₆.Particularly,Li₃Mg₂NbO₆ ceramics doped with 0.1 wt%BaCu?B₂O₅?sintered at 950°C for 4 hours can obtain the best microwave dielectric properties:?_r=14.27,Q×f=55521 GHZ and?_f=18.2ppm/°C.Besides,the doped ceramic has good chemical compatibility with silver.When the CuO doping amount is 0.5 wt%,the Li₃Mg₂NbO₆ ceramic can achieve excellent microwave dielectric properties at a sintering temperature of 950°C:?_r=15.03,Q×f=72135 GHZ and?_f=-23.01ppm/°C.?2?In this experiment,n-butanol was used as a solvent,polyethylene glycol octyl phenyl ether as a dispersant,polyvinyl butyral as a binder,and dibutyl phthalate as a plasticizer.The relationship between viscosity and thixotropy of the above organic additives is studied systemly,which is beneficial for obtaining a high-quality cast green sheet.When the solid content of the slurry is 60%,the dispersant is 2 wt%,the binder is11 wt%and the ratio of plasticizer to binder is 0.2,the BaCu?B₂O₅?-doped Li₃Mg₂NbO₆ceramic slurry can form a ceramic green sheet with a smooth surface and the same structure on both sides.?3?The accelerating voltage,beam spot size and the modes of SEM such as Backscattered Electron imaging and Backscattered Electron imaging in low vacuum mode,which all are closely relate to the quality image of the Micro-structure,especially in poor conductivity.This paper explores the effects of accelerating voltage and beam spot size on secondary electron images,backscattered electron images,and backscattered electron images in low vacuum mode of Li₃Mg₂NbO₆ ceramics.Finally,under the condition of the high-vacuum imaging mode with an acceleration voltage of10 kV and a beam spot size of 40,the secondary electron image of the SEM can clearly characterize the microscopic morphology of the Li₃Mg₂NbO₆ ceramic sample.