Fabrication Of Yag Transparent Ceramics By Solid-state Reaction Method

Yttrium aluminum garnet (YAG) is widely applied to solid-state laser because of its excellent optical performance. YAG is a candidate for applications of high-temperature structural materials and refractory coatings for electronic devices due to its low creep rate, high thermal stability and good chemical resistance, and it is widely used in lasers as a host for rare-earth-based phosphors, doped rare ionic YAG powder is used in fluorescent material and temperature meter. YAG crystal is usually synthesized by Czochralski, but its growth cycle is too long. In recent years, a lot of efforts have been made on synthesizing transparent polycrystalline YAG ceramics to replace the expensive YAG single crystals. In this dissertation, fully transparent YAG ceramics were fabricated by solid-state reaction method from commercial nano-sized Y2O3 andγ-Al2O3 powder.High-purity nanopowders of Y2O3 andγ-Al2O3 were used as starting materials. The starting materials were weighed to result in a chemical composition of Y:Al molar ratio=3:5 and mixed by ball-milling withΦ3mm ZrO2 balls in ethanol for 24h, with an addition of 0.5wt% tetraethyl orthosilicate (TEOS) as sintering aid. The mixtures were dried, sieved and calcined at 1200℃to obtain the mixture powders containing YAG and YAP. The mixtures powders were dry-pressed under 200MPa intoΦ16mm disks, then pre-sintered at 1300℃for 4h. The compacts were sintered at 1700℃for 5h and 24h in vacuum respectively. After sintering at 1700℃for 5h in vacuum, the average grain size is about 8.4μm. Pores were raely observed on the grain boundaries or in the grains. The in-line transmittance is about 52%(700nm); For the samples sintered at 1700℃for 24h in vacuum, the average grain size is about 12.2μm. The grain boundary is smooth. There is no pore in the fracture face, the in-line transmittance is about 76%(700nm).The different raw nano-materials of Al2O3 have a dramatic effect on synthesizing YAG transparent ceramics. In the identical preparing process, the in-line transmittance is about 76%(700nm) byγ-Al2O3 fabricating YAG transparent ceramics sintered 1700℃for 24h; but YAG ceramics by starting material ofα-Al2O3 is translucent. The different addition of TEOS (tetraethyl orthosilicate) has a dramatic effect in microstructure and optical properties of the sintered pellet. Sintering 1700℃for 5h, if there is no TEOS, pores are entrapped in the grain, the specimen is opaque; If the amount of TEOS is 3wt%, the abnormal growth of grain happened, the in-line transmittance is only 37.9% (700nm); If the amount of TEOS is 0.5wt%, the grain size is homogeneous, the ship is regular polygon, there are no pores in the grain and grain boundary, the relative density is theoretical value, the in-line transmittance is 60.8%(700nm).