Preparation Of LiMgPO₄,LiMgVO₄ And LiZnPO₄ Materials

In recent years,LiMgPO₄,LiMgVO₄ and LiZnPO₄ have attracted attention from scholars because of their low sintering temperature and excellent microwave dielectric properties,which meet the requirements of low temperature co-fired ceramics technology.At present,the solid state method is used to prepare these three materials in most of the research work.The solid state method not only requires a high reaction temperature,but also has the disadvantages of low purity of the prepared samples,irregular morphology and so on.Therefore,the above problems can be solved by optimizing the preparation method of the materials,thereby improving the properties of the materials.In this paper,the solid state method was used as a control experiment.LiMgPO₄ was prepared by molten salt method.LiMgVO₄ was prepared by sol-gel method.And LiZnPO₄ was prepared by modified precipitation method.At the same time,the preparation conditions are optimized for obtaining materials with or without low crystal impurity phase and good morphology.In this study,LiMgPO₄ was prepared by molten salt method.The effects of type of molten salt,type of magnesium source,type of lithium source,calcination time and calcination temperature on the crystal phase of the sample were investigated.And the effect of calcination temperature on the morphology of the sample were emphatically investigated.The results show that the best conditions of the LiMgPO₄ sample with minimal crystal impurity phase is in the molten salt of 50 wt%NaCl-50 wt%KCl,MgO as the magnesium source,LiOH as the lithium source,the calcination temperature of 750℃ for 2 h.In addition,the sample prepared at 750℃ have the best morphology,which are smooth polyhedral surface particles with good dispersibility.The sol-gel method using citric acid or acetic acid can prepare LiMgVO₄ at low temperature.It is found that the sol-gel method with acetic acid is superior to one with citric acid at reducing calcination temperature and improving morphology.Therefore,the effects of its preparation conditions,such as calcination temperature,calcination time and so on,on the morphology of the prepared sample were investigated.In order to obtain spherical LiMgVO₄with uniform and a size of about 100 nm,the optimum conditions is the calcination temperature of 600℃,the calcination time of 2 h.In the last chapter of the dissertation,a modified precipitation method was used to prepare rod-shaped LiZnPO₄ at low temperature.And the effects of calcination temperature,calcination time and type of acid on the prepared LiZnPO₄ were investigated.The results show that,compared with the solid state method,the modified precipitation method with acetic acid can reduce the calcination temperature from 700℃ to 500℃ and obtain a rod-shaped structure with controllable morphology.Under the calcination temperature of600℃,calcination time of 2 h,the prepared LiZnPO₄ displays regular rod morphology with diameter of about 2μm.