Silicon content in transparent YAG ceramics, analysis of the production process

Transparent ceramics are usually prepared with the use of a sintering aid, in the case of YAG mostly silicon in the form of SiO2 or TEOS. However, the presence of Si may lead to the formation of secondary phases or to the deterioration of optical and laser properties due to the presence of color centers. It is therefore important to know and control its content in the sintered material. In this work we analyze the quantity and distribution of silicon in transparent YAG ceramics produced by reaction sintering of a mixture of oxide powders under high vacuum. Silicon is added in the mixture as TEOS or nanometric SiO2 powder. Laser-induced breakdown spectroscopy (LIBS) was used to quantify and compare the silicon content after the various steps of the production process (i.e. in the as-shaped samples, after sintering and after air annealing). A strong decrease of Si concentration was observed after the vacuum sintering. TEM/EDX showed an increase of silicon content at grain boundaries after air annealing steps at elevated temperatures.