PhD thesis has been defended

The defense of the PhD thesis titled "Formation and structural-phase state of 1-4 at. % Nd3+:Y3Al5O12 laser nanoceramics" by Kosyanov D.Yu., the junior research scientist of Institute for Single Crystals of NAS of Ukraine, has been held on July 08, 2015.

Thesis for degree of Candidate of Technical Sciences in specialty 05.02.01. – Material Science. – Institute for Single Crystals NAS of Ukraine, Kharkiv, 2015.

Thesis is devoted to revealing regularities of phase- and structure formation, densification of 3-хY2O3–хNd2O3–5Al2O3 (х=0.03-0.12) oxide powders during reactive sintering of Y3Al5O12:Nd3+, as well as to determination of formation conditions of Y3Al5O12:Nd3+ (1-4 аt. %) laser nanoceramics.
An optimized synthesis temperature range of Y3Al5O12:Nd3+ phase formation (1200-1500 °С) at the reactive sintering of starting oxide powders is achieved in the powder systems with the following characteristics: D(Аl2О3)≈250 nm, disproportion parameter of particles R (D(Аl2О3)/D(Y2О3,Nd2О3))≈2.5 and 5. It has been shown that minimization of closed porosity value on the whole solid-state synthesis trajectory of
garnet phase (1500 °С) promotes stabilization of microstructure of compacts, which was realized for R≈2.5 powder system. Nd3+→Y3+ isomorphous substitution in the garnet structure (Y1-xNdx)3Al5О12 (x=0.01-0.04) for powder system with R≈2.5 has a threshold nature (starting from 1350 °С) with interaction between monoaluminates (Y1-yNdy)AlO3, (Nd1-zYz)AlO3 (y, z≤0.02) and alumina at 1200-1500 °С temperature range as a dominant mechanism. Segregation of zirconium ions along grain boundaries of Y3Al5O12:Nd3+ nanoceramics sintered at 1750 °С promotes stabilization of the
average grain size of 10 m at a concentration of residual porosity П<10-2 vol %. Laserquality Y3Al5О12:Nd3+ (1-4 at. %) nanoceramic have been obtained with the relative density ≥99.998 % and optical losses ≤10-1 cm-1 (λ=1.064 m), which are equal to those of corresponding YAG single crystals.

Keywords: nanopowders, diffusion-limited processes, different-sized particles, structural-phase state, sintering trajectory, laser nanoceramic.

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