Preparation Of Yttrium Aluminum Garnet (YAG) Transparent Ceramics

Yttrium aluminum garnet (YAG) single crystal has excellent chemical stability and optical properties, which is important solid-state laser host material, and widely used in scientific research, military, industrial and medical fields. However, the high cost of production, the long growth cycle and low doping concentration, all of these factors limited the application of single crystals. Compared to YAG single crystal, YAG ceramic laser material has several advantages, namely:(1)Ease of fabrication; (2)Fabrication of large size and high neodymium concentration; (3)Less expensive; (4)Multilayer and multi-functional ceramic structure; (5)Mass production, etc. Highly transparent ceramic materials will play a very important role in optical materials. In recent years, transparent ceramics have received much attention, researches mainly focus on the preparation of powders and ceramic technology.In this paper, YAG nano-sized powder was prepared by co-precipitation method using ammonium hydrogen carbonate as precipitants. The chemical composition of the precursor is mixture of Y2(CO3)3’nH2O and NH4AlO(OH)HCO3. The precursor directly converted to pure YAG after sintering at 900℃for 2 h, with no intermediate phases or other impurities generated. It is important to control the pH value at 8.0. The aluminum compounds precipitated prior to the formation of the yttrium compounds, then the yttrium compounds seemed to have precipitated onto the aluminum ones, forming a specific package structure and getting precursor with uniform composition. Choosing low concentration of stock solution, the obtained powders show narrow size distribution and good dispersion, with the average particle sizes less than 100 nm. To reduce the production of aggregates, precipitate were also washed repeatly with water and ethanol.Both isostatic pressing and dry pressing were used, isostatic pressing samples (100 MPa) were loose and porous, with honeycomb cross-section. When dry pressing was used, dense ceramic green body with uniform microstructure can be obtained under the pressure of only 30 MPa for 2 min. Meanwhile, the effect of pressure, holding time, compressing speed, water content and powder properties on the molding was researched.YAG transparent ceramics can be obtained by sintering under vacuum at 1750℃for 5 h. To explore the effect of powder properties, solid-state reaction method was also used for comparison. The results showed that the powders synthesized by precipitation method have high sintering activity, with small particles and good dispersion property. To further improve the transparency of ceramics, the factors such as the purity of raw materials, sintering technology and microstructure were also discussed.Synthesis of high-performance powders is one of the key factors for the preparation of YAG transparent ceramics, because the powder properties will have a direct impact on the followed molding and sintering performance. Preparation process, material properties and microstructure have influences among each other. So, in order to obtain transparent with high density, good optical properties, the internal relations must be considered when selecting the appropriate experimental parameters.