Preparation Of Nd: YAG Powders And Ceramics By Alcohol-water Co-precipitation Method

Nd-doped yttrium aluminum garnet (Nd:YAG), with excellent physical properties, superior optical and lasering characteristics, is the most important four-level solid-state laser host, and has been used widely in various areas, such as military, communications, metal processing, medical operations and others. The laser characteristics of Nd:YAG ceramics have been revealed to be nearly equivalent or superior to those of Nd:YAG single crystal. Moreover, Nd:YAG transparent ceramics has been an alternative to single crystal Nd:YAG as laser material.In this work, alcohol-water solvent co-precipitation was used to prepare YAG nano-sized powders and transparent ceramics. For the preparation of YAG powder, its technology and technical parameters were mainly studied, moreover the mechanism of preparing YAG powder was explored. For the sintering of Nd:YAG ceramics, sintering process and sintablity of the powder were mainly studied. The main points are as follows.YAG powders with excellent properties were prepared by alcohol-water co-prepparation method. The effects of concentration of reactant solutions, ratio of alcohol and water (R), co-preparation temperature, heat- treatment temperature, composition of precursors on the formation of YAG phase and powder properties were investigated by XRD, FT-IR, TG/DSC, TEM, and so on. Moreover, the mechanism of preparing YAG powder via alcohol-water solvent co-prepparation method was explored by these means.The results show that concentration of reactant solutions, ratio of alcohol and water and co-preparation temperature are very important for the formation of YAG phase and the properties of YAG powders. The precursor can be transformed from unformed state to crystal YAG without any intermediate phases, and the powder has excellent properties. In contrast, the precursor can be transformed to pure-phase YAG when the calcining temperature is higher than 1100℃under the same conditions. The reason is that the propertied are different between alcohol-water solvent and distilled water solvent. It is analysed that whether the prepursor are prepared by using alcohol-water solvent or distilled water solvent, the composition of precursor comprises Y₂(CO₃)₃ and Al(OH)₃. It indicates that precursors are were not changed owing to the use of alcohol-water. But compared with the results of distilled water system, homogeneity of Y and Al elements in the prepursor prepared by using alcohol-water was improved and the molar ratio of Y³⁺ to Al³⁺ is keeped at 3:5 in local areas. As a result, pure-phase YAG is directly formed without happening of solid-state reaction during calcining.Sintering ability of the powders and the factors on sintering were studied by the means of SEM and Ultraviolet spectrophotometer. The results show that sintering temperature and time of heat preservation are very important to obtain transparent ceramics, and the proper sintering temperature and time of heat preservation are 1750℃and 20 h respectively. Under proper sintering conditions, the sinter has high optical transmittance in visible light. Because sintering additive was not added during sintering, overquick grain growth causes that pores are surrounded by grains, grains of specimen are measured very large (several hundreds of micrometers). Compared with sinter-ability of the powder prepared using distilled water solvent, the sinter-ability of powder prepared using alcohol-water solvent are much better. The transmittances of specimens, prepared from the powders using alcohol-water with different R, increase with increasing R, but the optical transmittances of them did not change very much.. MgO with proper quantity using as sintering aid could control over-growth of grains and improve microstructures of ceramics.The above work was never reported.