Green bodies' porous structure, i.e. mesostructure, affects dramatically the functional parameters of the optical ceramics obtained by reactive sintering. Characteristics of the mesostructure are proposed to regulate by pre-annealing of green bodies at temperatures below the phase formation and consolidation. The approach was presented in the article published in Journal of the European Ceramic Society.
Developing an advanced technology and creating a new family of optical and, in particular, luminescent and laser ceramics is a fundamental scientific problem and a key task of modern ceramic materials science. Such materials are wanted to accurately measure distances (optical location), implement new modes of materials processing, create qualitatively new optical information carriers and medical equipment, IR windows, high-power LEDs and thermoelectric elements.
'The homogeneity of the mesostructure (inner structure) of green bodies, i.e. nanopowders compacted into pellets, from which ceramics were obtained, is one of the most important characteristics during sintering. For optical (laser) quality ceramic materials, it is necessary to achieve the removal of hundredths and thousandths of a percent of residual porosity in the final stage of sintering in order to ensure a low degree of light scattering. Control of the homogeneity of the initial compacts can be achieved by the variation of many technological parameters. For example, by changing the pressing technology, the choice, and mode of preparation of the initial nanopowders. However, a key feature of obtaining of the transparent ceramics by reactive sintering is that the energy transferred to the multi-component powder system, from which ceramics is obtained, is spent on the competing processes of phase transformations and consolidation. For this reason, we proposed to control the initial state of green bodies by annealing, prior to their sintering,' says Denis Kosyanov, head of the FEFU research team, a Senior Researcher of the National technology initiative Center for VR and AR (FEFU NTI Center).
The scientist noted that ceramic samples prepared from green bodies which pre-annealing at optimized conditions (600°C / 4 hours) exhibit porosity ?0.001 vol% and yield efficient laser emission at 1064 nm with a slope efficiency as high as 67% in quasi-continuous pumping at 807 nm (meet the level of world analogues).
Previously, scientists have already described this original approach in the Ceramics International journal on the example of the vacuum reactive sintered Y3Al5O12: Nd3+ laser ceramics.
The present work is to establish a more detailed correlation between the homogeneity of the initial green bodies, their structural-phase state and the functional parameters of the final materials.
FEFU runs a "Materials" priority project and NTI Center (grant No.1/1251/2018) within the framework of which researchers, among other things, reveal scientific and technological fundamentals for preparation of multifunctional ceramic materials for microelectronics, lighting engineering and radiochemistry.
The study was carried out by an international research group from Far Eastern Federal University (FEFU); Institute of Chemistry, Far Eastern Branch of the Russian Academy of Sciences; Institute of Single Crystals and Institute of Physics, National Academy of Sciences of Ukraine; and the National Institute of Laser, Plasma and Radiation Physics of Romania.
This work was partially supported by the Russian Science Foundation (Project No. 18-73-00145) and by Russian Foundation for Basic Research (Project No. 18-29-11044).