Co-precipitation Synthesis Of Yb:YAG Nano-powders And Fabrication Of Yb:YAG Transparent Ceramics

Compared with YAG single crystals,YAG polycrystalline transparency ceramics have the advantages of fabricating into larger size and doping with higher concentration of active ions which have a good application prospect in military and civil field.Therefore,YAG polycrystalline ceramics have become the hotspot of ceramic materials research field in recent years.This paper adopted co-precipitation method to preparate Yb:YAG nano-powder,and added silica as the sintering additives,then formed green body by dry pressing and cold isostatic pressing.Finally,obtaining Yb:YAG transparent ceramics by high temperature vacuum sintering.In the process of preparing transparent YAG ceramics are usually add silicon dioxide,so as to promote the densification and improve the optical property of the ceramic.However,about the precise mechanism of silicon dioxide,there are two kinds of views in academia:One view is that silica liquid melts at 1390? during sintering,thus the sintering mechanism change to be liquid phase sintering,so as to promote the densification of ceramic.While others argue that YAG is the stoichiometric ratio of compound and composition slightly off can cause the forming of mixed phase which will leading to a decline of the optical properties of the YAG ceramic.Silica sintering aids can increase YAG phase composition range,namely increasing the solid solubility of rare earth ions in YAG structure.This thesis aimed to investigate into the role of silicon dioxide in preparing YAG powder and YAG ceramics,and obtained the following main conclusions:SiO2 increased the solubility of rare earth ions in YAG crystal structure and aided the formation of YAG phase,but the overdose of SiO2 led to the formation of YAM phase;SiO2 increased the particle growth rates of YAG powders during high temperature calcination;SiO2 enhanced densification and increased the ceramic density,but the overdose of SiO2 led to the formation of secondary phases in ceramic microstructure.The optimum amount of SiO2 was 0.3 wt%;Calcination temperature was critical to the sintering activity of powders,here,the most suitable calcinations temperature was 1300?.Silica sintering aid joins into precursor in the form of coprecipitation method,Si4+ will distribute inside the grains,may not play the effective role of liquid phase sintering.Therefore this study proposes that silica sintering additives is coated on the surface YAG particles,forming a thin layer on the surface of powder particles.Thereby silica liquid phase distributes between the particles during sintering to promote the densification.The results showed that YAG powder coated with silica formed a continuous and amorphous layer on the surface;YAG diffraction peak intensity decreased with the increase of the amount of silica because of blocking effect of detection of X-ray by SiO2 membrane;Silica joined into Yb:YAG powder in the form of cladding could promote sintering,and the shrinkage percentage and the biggest shrinkage rate of green body raised obviously with the increase of the amount of silica;In addition,compared with the way of adding sintering additive by co-precipitation method,the transmittance of YAG ceramics increased significantly after vacuum sintering.In the process of preparation of YAG transparent ceramics,Y/Al always deviates from the stoichiometric ratio because of various reasons.In the process of grain growth,stoichiometric ratio elements gather at grain boundaries to form the second phase.Which will lead to the variation of structure of ceramic,spectral characteristics and physical property.Therefore,this thesis researched the influence of the composition segregation in Yb:YAG powder and ceramic structure.The researches showed that the second phase Al2O3 occured inside grain when A1 excess which will affected the optical performance of the ceramic seriously;YAG powder had pure phase when Y excess about 2.0at%,and ceramic samples had better microstructure.