Study Of Stereology On Microstrures Of Neodymium Doped Yttrium Aluminum Garnet Optical Ceramics

Compared with the same chemical composition,transparent neodymium doped yttrium aluminum garnet(Nd:Y₃Al₅O₁₂,Nd:YAG) ceramic has the advantages such as easy fabrication,low cost,large size,highly doped concentration,conveniently realizing the multi-layer and multi-functional ceramic structure,suitable mass production,and is becoming a new generation of laser materials to substitute the single crystals and to enlarge the laser matrix materials area.And it has the strategetic function in small,medium and large laser systems.Recently,materials researchers pay high attention on the manufacture method of Nd:YAG precursor powders and the sintering study of transparent ceramics and there are no transparent ceramics to satisfy the actual use domestically.In this thesis,the Nd:YAG precursor powders were synthesized by the LCS method,and the study was carried out on the YAG cubic crystal phase forming during the LCS process.The synthesized Nd:YAG precursor powders were high-energy vibratied milled and common,CIP molded into Nd:YAG green disks.The transparent Nd:YAG ceramic disks with 20mm in diameter and 1mm in thickness were prepared by vacuum sintering for 20h after being milled and polished.The transparent ceramic disks as prepared with the optical transmittance 82.45%at 1064nm are close to that of single crystals with the same thickness.The mearsurements were carried out on the properties of Nd:YAG transparent ceramics and the quantitative relationship between the stereological parameters of Nd:YAG transparent ceramic microstructures and optical transmittance were studied by the computer software,the main results are given below:1.The nano-sized Nd:YAG cubic crystal phase precursor powders were synthesized by LCS method at 1100℃,the powders were finely dispersed and particles size was below 100nm,as builds a good foundation for being pressed and lowering the sintering temperature;2.The high-energy milling being used in mechanically alloying was put on the as-synthesized precursor powders,and the high density green disks were pressed by CIP method; 3.By strictly cotrolling the sintering processes,the vacuum method was used on the Nd:YAG,The transparent ceramic disks as prepared with the optical transmittance 82.45%at 1064nm are close to that of single crystals with the same thickness,as sets a good basis for micro-plate solid lasers;4.The main study was carried on the stereology which has been developed in recent years.The stereology was used to quantitavly study the relationship between the the stereological parameters of Nd:YAG transparent ceramic microstructures and optical transmittance were studied by the computer software,the main results are:(1) With the increasing of three dimensional sphere diameter,the transparency of Nd:YAG climbed,when the value reaches 20μm,the transparency of ceramics was consistent to that of single crystals.The relationship between sintering temperature and times is linear increasing,but when the sintering temperature reaches 1750℃, the increasing trend decreases;(2) With the increasing of mean specific area of grains per volume S_v and mean specific area of single grain S_vp,the transparency decreased.Under 1750℃,S_v and S_vp,keep the same change,but above 1750℃,S_v decreases linearly with increasing of optical transmittance,and S_vp decreases poly-exponentially with increasing of optical transmittance;(3) With the increasing of three dimensional mean free distances of grain boundary,namely the grain boundary width,the transparency decreased.The sintering temperature has different effect on three dimensional mean free distances of grain boundary.Under 1750℃,λdecreases by the second exponential trend with increasing of optical transmittance,but above 1750℃,λdecreases by the linear trend with increasing of optical transmittance;(4) The study on the relationship between above four parameters and optical transmittance has the same result:under 1750℃,the grains in the green disks grow simultaneously,but above 1750℃,the grains grow by the rearrangment of grains.(5) With the increasing mount of doped Nd iron,the acess amout of Nd iron distributes on grain boundary as homogeneous phase,and prevents the grain growth, increases the grain boundary,increase the irregularity of grain and hence decrease the optical transmittace of Nd:YAG ceramics.The ideal doped amount of Nd iron is 1at%,the SiO₂ additive can reduces the grain irregular changes.