Sol gel synthesis and spark plasma sintering of lanthana-doped alumina glass

Abstract Amorphous materials of eutectic composition in the La2O3–Al2O3 system were prepared from powders synthesized by the sol–gel method and then flame sprayed to form amorphous transparent beads ~ 10–150 μm in diameter. These were subsequently consolidated by the spark plasma sintering (SPS) method. The final density of sintered samples showed a dependence on temperature and the applied pressure. The transmittance increased with temperature up to 860 °C, then decreased with further increase in temperature, as a consequence of crystallization. The measured glass transition and crystallization temperatures, Tg and Tx, are 845 and 905 °C, respectively. Crystallization below Tx is likely the consequence of the applied electric field during sintering. The highest observed transmittance in the red-end of the visible region (650 nm) was determined to be about 40%. The transmittance of sintered amorphous samples in the IR region was between about 50% and 60% with a significant broad absorption band at about 2.9 μm. The occurrence of this band is attributed to the stretching of the O―H bond of residual OH species in the samples.