R.P. Yavetskiy

Low-agglomerated yttria nanopowders via decomposition of sulfate-doped precursor with transient morphology

Abstract The fabrication peculiarities of low-agglomerated yttria (Y2O3) nanopowders via thermal decomposition of sulfate-doped precursor with transient morphology were studied. It was determined that Y2(OH)5(NO3)x(CO2)y(SO4)z·nH2O (n=1-2) crystalline precursor underwent fragmentation and decomposition into isolated quasi-spherical Y2O3 particles upon calcination. Effect was connected with minimizing the free energy of the plate-like crystallites via reducing the contact surface until to the moment of spheroidization and attainment of isolation that occurred at T=1100 °C. Residual sulfate ions slowed down the surface diffusion during heat treatment thus retaining quasy-spherical morphology and low aggregation degree of Y2O3 nanopowders. Sulfate-doped yttria nanopowders with medium particle size of 53±13 nm possessed improved sinterability in comparison with undoped ones arising from finer particle size, narrower particle distribution and lower agglomeration degree.

Nd3+:Y3Al5O12 laser ceramics: Influence of the size of yttrium oxide particles on sintering

The influence of the size of Y2O3 powder particles on the structure formation and densification of Nd3+:Y3Al5O12 laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd3+:Y3Al5O12 phase. Bulk swelling of pressed samples during sintering of 2.94Y2O3-0.06Nd2O3-5Al2O3 powders with the size ratio of the initial particles R(Al2O3/Y2O3) ∼ 5 is observed. The application of different-sized powders (R ∼ 2.5) provides quantitative ratios between phases in the 3Y2O3-5Al2O3 system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd3+:Y3Al5O12 have been obtained by the solid-phase sintering of oxide powders (R ∼ 2.5). The slope efficiency for 1 at % Nd3+:Y3Al5O12 laser ceramics is found to be 33%.

Transparent 4 at% Nd3+:Y3Al5O12 ceramic by reactive spark plasma sintering

Neodymium doped yttrium aluminum garnet 4 at% Nd3+:Y3Al5O12 transparent ceramic was first fabricated by reactive spark plasma sintering using commercially available α-Al2O3, Y2O3, Nd2O3 powders as starting materials. Optimized sintering conditions were included two-steps: 1000 °C/3u2005min/100 °C min−1 and 1350 °C/5u2005min/30 °C min−1. 4 at% Nd3+:Y3Al5O12 ceramic had a homogenous microstructure with average grain size of 710u2005nm, and exhibited over 75 % transmittance in the visible wavelength range.

Fabrication and characterization of 1–4 at.% Nd 3+ :Y 3 Al 5 O 12 Laser Ceramics by solid-state reactive sintering

Peculiarities of phase formation and densification processes during reactive sintering of Nd3+:YAG laser ceramics prepared using particles with different size have been studied. It has been found that utilization of submicron powders can significantly reduce YAG formation temperature from 1700°C for coarse powder to 1200-1500°C for fine powders. Moreover, utilization of different-sized yttria and alumina particles provide a competitive advantage of shrinkage over expansion processes by changing the kinetics of YAG phase formation. Nd3+:YAG (1-4 at.%) laser ceramics with in-line optical transmission of about 81.5 % at λ=1064 nm has been produced by reactive sintering. Finally, we succeed in lasing of Nd3+:YAG (4 at.%) ceramics under pulsed laser diode pumping.

Comparison of Nd:YAG optical ceramics produced by different sintering routes

Nd:YAG ceramics were fabricated by solid-state reactive sintering of commercial powders and vacuum sintering of custom made co-precipitated nanopowders. The densities, microstructure, average grain size, residual porosity, optical transmittances of the sintered ceramics were compared. Nd:YAG ceramics produced by solid-state reactive sintering possess higher transmittance compared to vacuum-sintered ceramics from co-precipitated nanopowders, which is however still lower than that of single crystals. The possible ways to improve optical quality of Nd:YAG ceramics are discussed.