Study On Nd～(3+) Doped Garnet Transparent Ceramics

Yttrium aluminum garnet (Y3Al5O12, YAG), belonging to cubic system with no birefringence effect, can be used as high-temperature ultraviolet and infrared windows because of its high melting point, outstanding creep resistance and excellent thermo-mechanical properties. Active ions doped YAG can also be used as excellent laser materials. It can generate different wavelength laser with corresponding ions. Until recently, Nd:YAG laser has always been the most popular solid-state laser light source. Gadolinium gallium garnet (Gd3Ga5O12, GGG) single crystal has high thermal-shock resistance though its thermal conductivity is smaller than that of YAG single crystal. Furthermore, the separation coefficient of Nd3+ in GGG crystal is high and easy to reach high doping concentration. This is very important for high power laser. However, the processing of single crystal is very complex, it need not only much time but also an expensive Ir crucible. Furthermore, it's hard to reach large size single crystal. Compared with single crystals, transparent laser ceramics have attracted more attention because of their ease of manufacture, low cost and scalability.In this dissertation, polycrystalline nano-sized Nd:YAG ceramic powders were synthesized via a low temperature combustion and chemical co-precipitation methods.The sinterability of Nd:YAG powders was also investigated.1. Preparation of Nd:YAG ceramic powdersPolycrystalline nano-sized Nd:YAG ceramic powders were synthesized via a low temperature combustion method and chemical co-precipitation method respectively. For chemical co-precipitation method, tetraethylenepentamine was used as precipitant for the first time to synthesize pure phase YAG powders. In addition, influences of different dispersers, reactant concentration, primary reaction temperature on the morphologies of Nd:YAG ceramic powders were also studied with ammonium hydrogen carbonate (AHC) as the precipitant. In this paper, AHC was mainly used as precipitant to synthesized nano-sized Nd:YAG ceramic powders.For low temperature combustion method, influences of different burning reagent on the morphologies of Nd:YAG ceramic powders were studied. The process of preparing Nd:YAG ceramic powders via citric acid as burning reagent was specially investigated. The results showed that pure phase Nd:YAG nano-sized powders could be directly obtained at 850oC with no any intermediate phases formed.2. Sintering of Nd:YAG ceramicThe sinterability of Nd:YAG nano-sized powders synthesized via a low temperature combustion method and chemical co-precipitation method were studied by vacuum sintering technique. The results showed that Nd:YAG powders synthesized via AHC chemical co-precipitation method had good sinterability. The largest transmittance of resultant YAG ceramic sample in the visible light region nearly reached 40%.The micro-structures of our ceramics and Japanese transparent laser ceramics were compared. The results showed that the grain size of the Japanese transparent laser ceramic, which was only 0.5-1.5μm, was smaller that that of our ceramic.In addition, Nd:YAG ceramics were also prepared via solid state sintering method. With Y2O3 powders synthesized via oxalic acid chemical co-precipitation and commercial A12O3,Nd2O3 as raw materials, Nd:YAG ceramics were obtained using solid state sintering method at 1750oC for 7h.3. Preparation of Nd:GGG powdersPolycrystalline nano-sized Nd:GGG powders were synthesized via a low temperature combustion method and chemical co-precipitation method respectively. For low temperature combustion method, pure phase Nd:GGG nano-sized powders could be directly obtained at 750oC with citric acid as burning reagent, which was the lowest temperature that had never been reported by far. Additionally, pure phase Nd:GGG powders with a particle size 40nm, which is spherical or near-spherical, could be directly obtained at 750oC.