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In the last
several decades, nanometer sized materials have attracted much attention due to
their interesting size dependant properties and various applications in
optoelectronics, memory storages, chemical industry and bio-medicine.
We utilize nanoscale materials concept for transparent ceramics fabrication. The
tremendous interests to such materials appeared in the middle of 90s, when
Japanese pioneer groups of (A. Ikesue) and (K. Ueda, T. Yanagitani) reported,
for the first time, the lasing effect in transparent ceramics materials. These
materials consist of tightly packed, randomly oriented crystallites and they
become transparent when the density of scattering centers is low. Presently,
revolutionary laser ceramics of any required size and Ln3+ activator
concentration has allowed the achievement of kilowatt level of CW laser output
with LD pumping.
Our research in this project is focusing on two parts: the synthesis of
nanometer sized ceramics powder, their characterization and control engineering
of consolidation, packing of produced nanoparticles utilizing various methods,
including uniaxial pressing, Cold Isostatic Pressing (CIP), slip casting with
various additives and possibly high power ultrasound action.
Primarily, our efforts are concentrated on fundamental understanding of the
influence of particles size, shape, degree of aggregation, their surface states
on the physics and chemistry of the processes of nanoparticles packing via
either particle-particle fusion at high temperature in vacuum, or self-assembly
at ambient temperature.
Preliminary, we perform research on well known oxide laser materials as Yttrium
Alumina Garnet - YAG (Y3Al5O12) doped with
Neodymium (Nd3+). We are using different methods of nanoceramics
powder preparation, including established method of coprecipitation, combustion
and two phase reaction. The route of powder preparation, synthesis conditions
are reflected in the final product phase purity, particles size. The structural
information of produced samples is obtained via XRD, solid state Al27
NMR, Raman spectroscopy. Particle size is estimated via TEM measurements. YAG
solid state phase diagram has a complex structure with high temperature
formation. Besides YAG, other stable phases are YAP (YAlO3) and YAM
(Y4Al2O9). When particles sizes are small, any
kind of structural lattice distortions (like bond lengths, angle tilts, cation
site populations) can be expected. So, we believed that major challenge of the
transparent ceramics fabrication is to balance the degree of the order-disorder
of internal structure of nanocrystallites as well as when they are tightly
packed in compact composite.
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(b)
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The
representative TEM images of YAG precursor (a) and YAG nanocrystallites (b)
prepared via the method of two phase reaction.
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