Preparation Of LiMVO₄（M=Mg,Zn） Materials

Both Li ZnVO₄ and LiMgVO₄ are microwave dielectric ceramic materials which have ultra-low sintering temperature.Because they could meet the requirements of ULTCC technology,there are more and more scholars start to pay attention to those materials.However,at present,the conventional solid-state method is always used to prepare the two materials.Solid-state method has the disadvantage of higher calcination temperature,longer holding time,and it is difficult to control the size and morphology of the particles.In addition,the sample obtained by this method always has low purity and large particle size.Therefore,in order to reduce the preparation temperature of the materials,increase the purity of the sample,reduce the particle size,and regulate the morphology,the preparation method of materials could be optimized.In this paper,Li ZnVO₄ material was prepared by sol-gel method and LiMgVO₄material was prepared by molten salt method.At the same time,the effects of different preparation conditions on the crystal phase and morphology of the material were investigated.In this study,LiZnVO₄ material was prepared by sol-gel method,and the effects of citric acid dosage,heating temperature of waterbath,pH value of sol,and calcination temperature on the crystal phase and particle size of the obtained samples were investigated.The results show that the sol-gel method could reduce the preparation temperature of Li ZnVO₄ material to 500°C.At the same time,the sample has higher purity and crystallinity,and the particle size is smaller than solid-state method,the average size is 2μm.Apart from that,the particle size is increasing with the calcination temperature improving.When the optimized citric acid dosage is 1:1.5,the heating temperature of waterbath is 65°C,and the pH value of sol is 4,the higher purity and higher crystallinity sample could be obtained.The LiMgVO₄ material,which has flaky morphology,was prepared at low temperature with using KNO₃ as the molten salt.And the effects of the conditions,such as calcination temperature,holding time,and the amount of molten salt,on the flaky morphology of LiMgVO₄ were investigated.The results show that the flaky morphology of LiMgVO₄ could be obtained at low temperature of 350°C,the size of the flaky LiMgVO₄ is 1²μm and the thickness is less than 100 nm,but the shape of the flaky particles is irregular.The suitable calcination temperature to obtain the flaky LiMgVO₄ with good shape is 350°C,the holding time is 3h,and the ratio of molten salt is 1:1:1:5.In the last chapter of the paper,the LiMgVO₄ material,which has rod-shaped morphology,was prepared at low temperature with using NaNO₃-KNO₃ as the mixed molten salt.And the effects of the conditions,such as calcination temperature,holding time,the amount and type of molten salt,on the shape and size of LiMgVO₄ nanorods were investigated.The results show that the preparation temperature of LiMgVO₄ material is reduced from 600°C to 300°C by molten salt method,and the diameter of the obtained LiMgVO₄ nanorods is 50¹00 nm,the length is 200⁶00 nm,the aspect ratio is 4¹0respectively.Since the preparation conditions play an important role in controlling the morphology of the sample,in order to prepare Li MgVO₄ nanorods with complete shape and uniform particle size,the optimized calcination temperature should be 300°C,the holding time should be 3h,the molten salt ratio should be 1:1:1:5,and the NaNO₃-KNO₃ must be used as the molten salt.