Spark plasma sintering and decomposition of the Y.sub.3NbO.sub.7:Eu phase

The spark plasma sintering (SPS) of Eu.sup.3+-doped Y.sub.3NbO.sub.7 niobate phase was investigated to obtain dense ceramics. Although SPS allowed obtaining high-density ceramics, decomposition of the niobate phase occurred at high temperature and was promoted by the SPS process, which limited its use as an optical material. The niobate phase has been prepared by two synthesis methods: a solid-state route and a sol-gel method. The purity, density and microstructure of the dense ceramics were analyzed after spark plasma sintering. Translucent ceramics were only obtained from sol-gel powders after SPS at 1600 °C during 20 min with a heating rate of 5 °C/min. The sintering study of the pure niobate phase showed that during SPS process and especially in the presence of the high electrical field the Y.sub.3NbO.sub.7 phase is metastable at 1600 °C. A decomposition of the niobate compound is clearly demonstrated by luminescence measurements when high heating rates were used.