Microstructure and photoluminescence of transparent luminescent ceramics YNbO4 obtained by uniaxial hot pressing and conventional sintering from crystal powders synthesized by sol-gel
Description
Ultrafine YNbO4 powders were synthesized by the sol-gel. High-purity fluoride Nb-containing solutions were taken in volumes corresponding to the specified value of Nb. Niobium hydroxides were precipitated with ammonia from these solutions. The precipitates were washed with deionized water to remove NH4+ and F- ions and dried at 100°С. After that precipitates were mixed with a Y(NO3)3 solution of a given Y concentration. A 25% solution of NH4OH was introduced into the resulting pulp with stirring; pH was adjusted to 8 – 9. The residue was filtered off, washed with deionized water, dried at ~ 110-120°C, and then three separate portions were sintered at temperatures ~ 1000, ~ 1100, ~ 1180°C for 3 h. Control YNbO4 ceramic samples were obtained by conventional sintering (CS) by sintering in a resistance furnace (Nabertherm GmbH, Germany) at 1400°C for 5 h. The samples were prepared from sol-gel powders sintered at 1180°C. Powders prepared at three different temperatures were prepared by uniaxial hot pressing (UHP) in three different regimes, so that we could choose the best UHP conditions for preparation of translucent YNbO4 ceramic samples. The regimes were the following: Regime 1 - Tsint = 1140ºC, P = 400 kg/cm2, τsint = 40 min; Regime 2 (double application of pressure) - T1sint = 1080ºC, P1 = 200 kg/cm2, τ1sint = 60 min; T2sint = 1180ºC, T2 = 200 kg/cm2, τ2sint = 50 min; Regime 3 - Tsint = 1180ºC, P1 = 220 kg/cm2, τsint = 60 min.