Preparation of infrared transparent YAG-based glass-ceramics with nano-sized crystallites

Transparent YAG-based glass-ceramics were prepared by a novel method called amorphous sintering followed by controlled crystallization (ASCC) from the compositions of 62.5Al2O3–(37.5 − x)Y2O3–xLa2O3 (in molar ratio, x = 5, 7, 10 and 20). The stability of the YAG glass was improved by the incorporation of La2O3, which increased the activation energy for crystallization. With 10 mol% La2O3, bulk YAG glass was prepared by hot-pressing and showed an infrared transmittance of 66%. The YAG glass was converted into glass-ceramics by post annealing at 875 °C for 5 h for controlled crystallization. The obtained glass-ceramic sample showed a crystallite size of 20–50 nm and an infrared transmittance of 60%. With increasing annealing time, the crystallites grew up quickly, resulting in a significant decrease in transparency. In the hot-pressed glass, nano-sized YAG nuclei (∼5 nm) were found, which were probably responsible for the crystallization behavior observed at temperatures (e.g. 875 °C) below the onset crystallization temperature.