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Transparent yttrium aluminum garnet (Y 3(1+ x ) Al 5 O 12 ) ceramics with different deviations from stoichiometry were fabricated by solid-state reactive sintering of commercial powders. The influence of non-stoichiometry on phase composition, microstructure, grain growth kinetics and optical transparency of the ceramics were studied. It was found that for Al 2 O 3 -excess samples, the transmittance and the average grain size decreased sharply due to the Al 2 O 3 secondary phase. For the stoichiometric sample sintered at 1760 °C for 10 h, the highest transmittances of 83.1% at 1064 nm and 80.2% at 400 nm were obtained. For Y 2 O 3 -excess samples, when the excessive content was smaller than 0.7 mol%, the transmittance decreased slightly and the average grain size increased. However, when the deviation was larger than 0.7 mol% the transmittance and the average grain size decreased due to the secondary phases.

Well-dispersed yttria nanopowders were synthesized by a precipitation method from yttrium nitrate solution using ammonium hydrogen carbonate as a precipitant. Needle-like precursor Y 2 (CO 3 ) 3 ·2.79 H 2 O undergoes fragmentation and decomposition into isolated quasi-spherical Y 2 O 3 particles upon calcination in air. Highly transparent YAG ceramics were fabricated from the as-synthesized Y 2 O 3 powder and the commercial α-Al 2 O 3 powder by vacuum sintering. Phase transformation, morphology evolution, and sinterability of Y 2 O 3 powders, microstructure and optical properties of YAG ceramics were investigated in detail. The densification, grain growth, linear shrinkage and phase transformation of the as-sintered ceramics were also explored. The activation energy for grain growth in the ceramic sample is 881 kJ/mol. With optimized preparation conditions, YAG ceramics with the average grain size of about 20 μm were fabricated by sintering at 1780 °C for 20 h, whose in-line transmittance reached 83.7% and 80.3% at the wavelength of 1064 nm and 400 nm, respectively.

Transparent polycrystalline YAG ceramics were fabricated by solid-state reactive sintering of a mixture of commercial α-Al2O3 and Y2O3 powders with tetraethoxysilane (TEOS) and MgO as sintering aids. Pressed samples were sintered from 1500 °C to 1750 °C in vacuum. Phase transformation, densification, microstructure evolution, grain growth kinetics and optical transparency of YAG ceramics were examined. Fully dense YAG transparent ceramic with average grain size about 17 μm was obtained by vacuum sintering at 1730 °C for 10 h and the in-line transmittance of the sample was 80.9% at 1064 nm wavelength. The maximal transmission 82.8% was demonstrated for the sample sintered at 1730 °C for 20 h, whose average grain size was about 22 μm. These pure YAG ceramics can be used for optical windows applications.

Undoped and Nd- or Yb-doped laser-grade yttrium aluminum garnet and (Y,La)2O3 ceramics with a transmittance above 80% in the 1-μm lasing region have been prepared by solid-state reactions using nonagglomerated Y2O3 and Al2O3 nanopowders. The Y2O3 nanopowders were prepared via laser evaporation, chemical precipitation from urea solutions, and grinding of commercially available Y2O3 in a purposedesigned laboratory-scale attritor at stirrer rotation rates of up to 1500 rpm. The YAG ceramics were prepared using commercially available Al2O3. After grinding, all of the powders had a particle size on the order of a hundred nanometers. Green compacts produced from the nanopowders were sintered in a vacuum furnace between 1615 and 1750°C to give highly transparent ceramic samples.

Polycrystalline Nd:YAG ceramics were fabricated by the solid-state reaction and vacuum sintering method using Y2O3, α-Al2O3 and Nd2O3 as starting powders. These powders were mixed in ethanol doped with MgO and TEOS and ball milled for different time periods. The samples were sintered from 1500 °C to 1760 °C for 0.5–20 h. Effects of ball milling time on the particle size of powder mixtures as well as ceramics densification process, microstructure evolution and optical transparency of the as-prepared Nd:YAG ceramics were mainly investigated. It was demonstrated that coarse powders can be ground into fine particles. Porosities of Nd:YAG ceramics sintered at 1600 °C and 1760 °C decrease with the increase of ball milling time up to 12 h and are kept almost unchanged with further increasing the time. Contamination of the powders with impurities, which may not be observed in microstructures, when the ball milling time is overlong, and the very few residual micro-pores, will cause an infinitesimal decrease in transmittance. The grain growth kinetics of Nd:YAG ceramics fabricated from the optimal ball milling process was also studied in this paper. The highest in-line transmittance of 83% at 1064 nm was obtained by sintering the sample at 1760 °C/3 h from the powder mixtures ball milled for 12 h.

The physicochemical properties of Y2O3 and Al2O3 nanopowders produced by the laser synthesis were studied. Carbonate and nitro groups along with bound water are formed on the surface of the Y2O3 nanopowders, whereas only nitro groups are formed in the case of Al2O3. After calcination of the nanopowders at temperatures higher than 750 °C in air followed by cooling to room temperature, the nanopowders repeatedly sorb H2O and CO2. The influence of commercial dispersant Dolapix CE64 on the stabilization of aqueous dispersions of the Y2O3 and Al2O3 nanopowders was studied. The obtained results can be used in colloidal methods of compacting optical ceramics.

To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 °C a pure single-phase solid solution Yb 3+ :(La x Y 1− x ) 2 O 3 was formed in the nanoparticles. Influence of lanthanum oxide as an isovalent additive on the yttria structure was investigated. The lanthanium ions were proved to be a good aid to sinter yttria ceramics doped with Yb 3+ at moderate temperatures about 1650 °C. The ceramics with relative density higher than 99.99% and grain size about 40 μm were fabricated. Full transmittance of 1.8 mm thick Yb 0.11 La 0.23 Y 1.66 O 3 ceramics reached 82.5% at 800 nm. This material could be a good gain medium for ytterbium high power pulse lasers.

To produce highly transparent Yb-doped yttrium lanthanum oxide (Yb3+:(LaxY1–x)2O3) ceramics two original technologies were used: laser synthesis of nanopowder and pulsed magnetic compacting. Sintering of the compacts in vacuum 3×10–4 Pa at 1600–1700 °C during 13 hours led to transparent ceramics fabrication. The ceramics with relative density higher than 99.99% and grain size about 40 µm were fabricated. Full transmittance of 1.8 mm thick Yb0,11La0,23Y1,66O3 ceramics reaches 82.5%@800 nm. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Methods for synthesis of nanosized precursors for the preparation of yttrium-aluminum garnet from organic-inorganic derivatives of yttrium and aluminum have been developed. It has been shown that most of the methods for carrying out the process result in the formation of precursors with high specific surface area. The precursor obtained using nanosized powder of aluminum oxide and yttrium acetylacetonate is the least agglomerated. The data obtained can be used when preparing optical ceramic from yttrium-aluminum garnet.

About new technology of production of transparent ceramics including laser synthesis of nanopowders, their magnetic pulsed compaction and vacuum sintering is reported. The results of investigations of the synthesized samples of transparent ceramics made from neodymium-activated yttrium oxide are presented. It has been shown that in a 1.1 mm thickness sample with optical loss coefficient α1.07μm = 0.03 cm−1 laser generation at λg ∼ 1.08 μm with a slope efficiency of 15% at laser diode pumping at a wavelength of 807 nm has been obtained.

The results of investigations of mechanical, optical and laser characteristics of ceramics made from neodymium-activated yttrium oxide are presented. The ceramics were fabricated with the use of a new technology including Laser synthesis of nanopowders and their magnetic pulsed compaction (LSN&MPC). The fracture toughness (K 1C = 0.9-1.4 MPa m 1/2 ) and microhardness (H v = 11.8 GPa) of the ceramics have been determined. It has been found that ceramic samples sintered in the temperature range from 1550 to 2050 °C have (1-150) vol. ppm porosity and optical loss coefficient in the range from 0.03 to 2.1 cm -1 . It has been shown that pore content in this range did not influence on the optical loss coefficient. Laser generation at λ g ≈ 1.079 μm with a slope efficiency of 15% under laser diode pumping has been obtained in 1.1 mm thickness sample with α 1.07 μm = 0.03 cm -1 .

We studied mechanical, optical, and lasing parameters of neodymium-doped yttrium oxide ceramics synthesised by using a new technology involving the laser synthesis of nanopowders and their magnetic pulsed compaction. The fracture toughness of ceramics to cracks and its microhardness were measured to be KIC = 0.9—1.4 MPa m1/2 and Hν = 11.8 GPa, respectively. Ceramic samples sintered in the temperature range from 1550 to 2050°C have the porosity (1—150)×10-4% and the optical loss coefficient α1.07 = 0.03—2.1 cm-1 at a wavelength of 1.07 μm. It is shown that such porosity does not affect the optical loss coefficient of light. Lasing at ≈1.079 μm with a slope efficiency of 15% was obtained in a 1.1-mm-thick sample pumped by laser diodes.

The possibility of synthesizing technological Nd 3+ Y 2 O 3 and Y 2 O 3 optically transparent ceramics is studied. This technology is different from the conventional approaches, because the compacting was performed using the uniaxial static compression with ultrasonic treatment of the compacted nanopowder. It was found that the relative compact density in the case of compaction of weakly agglomerated powders with an average parti- cle size of about 10 nm varies in the range from 0.48 to 0.58 depending on pressure (240-720 MPa), and it weakly depends on the ultrasonic treatment. At the same time, using ultrasound for nanopowder compaction allowed enhancement of the optical properties of ceramics and indeed race in its radiation attenuation factor at the wavelength of 1.06 µ m from 8.26 to 2.53 cm -1 . The radiation attenuation is related to the scattering centers observed in the samples: pores and inclusions with a content of about ~10 -2 and 10 -3 vol %, respectively, as well as the compaction defects that play a predominant role in the process. It is pointed out that the developed approach is promising for manufacturing large-volume, optically transparent ceramics.

The design and characteristics of a setup for producing metal oxide nanopowders with an output of up to 20 g/h are discussed. The grain mean size in the powders is 15 nm, and the radiation power consumption is 30—40 (W h)/g. Y2O3-stabilized ZrO2 (YSZ) and Al2O3 + YSZ nanopowders are prepared by target evaporation with a pulse-periodic CO2 laser, followed by vapor condensation in an air stream. The mean power, peak power, and efficiency of the pulse-periodic CO2 laser, excited by a combined discharge, are, respectively, 1 kW, 10 kW, and ≈10%. Data for the powder specific surface, grain shape, and grain size distribution, as well as results of X-ray phase and structure analysis, are reported.

The results of investigations of mechanical, optical and laser characteristics of ceramics made from neodymiumactivated yttrium oxide are presented. The ceramics was fabricated with the use of a new technology including L aser s ynthesis of n anopowders and their m agnetic p ulsed c ompaction (LSN&MPC). The fracture toughness Κ IC = 0,9 - 1,4 MPa•m 1/2 ) and microhardness (H V = 11,8 GPa) of the ceramics have been determined. It has been found that ceramic samples sintered in the temperature range from 1550 to 2050°C have (1 - 150) vol. ppm porosity and optical loss coefficient α 1,07 μm = 0,03 - 2,1 cm -1 . It has been shown that pore content in this range did not influence on the optical loss coefficient. Laser generation at λ g ≈ 1,08 μm with a slope efficiency of 15 % at laser diode pumping has been obtained in 1.1 mm thickness sample with α 1,07 μm = 0,03 cm -1 .

Our paper reports about YSZ powders by successive evaporation and crystallization in the gas stream. In the laser applied the original method of active medium excitation was used. Efficiency of the laser constructed on the basis of this method reached 22 percent and specific power output at approximately 1 W/cm3. Pulsed regime is proved to be more efficient for active medium excitation and target evaporation than continuous one. Targets made from coarse YSZ powder with Y2O3 content of 10.15 mol. percent were evaporated and crystallized in a stream of cleaned air. Cubic-structure YSZ particles were obtained which had a shape close to spherical. Particle size distribution was close to a lognormal distribution with dg equals 10 nm and (sigma) equals 1.75. Specific surface of the powder was up to 70 m2/g, while the Y2O3 content reduced to 9.8 mol. percent.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pulsed cathodoluminescence of Nd3+:Y2O3 ceramic synthesized from nanopowders obtained by laser evaporation of a solid target has been investigated in the 350-850-nm range. The samples were sintered in vacuum furnaces at temperatures of 1550-2050°C, but with different heating rates: 5K/min (first group) and 0.75K/min (second group). Strong luminescence bands of the Nd3+ ion showed up in the samples of the second group at λ≈425 and 457nm. A wide emission band at λ≈485nm of the intrinsic center predominates in the samples of the first group, while the luminescence bands of neodymium become weaker as the sintering temperature of the samples increases. It is shown that the appearance of the bands at λ≈425 and 457nm is associated with the presence in the ceramic of an impurity, most likely the monoclinic γ-Y2O3 phase, concentrated in micron-size regions along the edges and at the junction points of the crystals.