Polycrystalline Optical Material Group
STAFF
MORITA, Koji; TODOROKI, Shin-ichi; LI, Jiguang; VASYLKIV, Oleg（Staff Tabs）
AIM and GOAL
- Optical materials for sensor windows and light sources are one of key components for realizing smart society. Our group is aiming to develop new polycrystalline optical ceramics that possess excellent mechanical and thermal properties in addition to visible to near-infrared broadband transmission.
- In order to attain a major breakthrough in the optical ceramics, our group are now focusing on complex composition systems as a new challenging field of the optical ceramics.
APPROACH
- New optical materials : By expanding the search area from simple composition systems to unexplored complex composition systems, we are expecting to develop new optical ceramics that possess excellent mechanical and thermal properties in addition to broadband transmission.
- Bulk processing : We are aiming to develop densification techniques that enable to synthesize polycrystalline optical ceramics with complex composition systems through utilizing external field effects such as current/electric field and high pressure.
- Applications : New polycrystalline optical ceramics applicable to broadband sensor windows and light sources.
FIG 1 Application examples of optical ceramics in sensing windows and light sources for realizing smart society.
FIG 2 Examples of (b) high strength alumina/spinel laminated composite and (c) cross-sectional interface microstructure fabricated through (a) a pulsed current sintering technique, and (d) (Y,Gd)2O3:Eu3+ transparent polycrystalline ceramics and (e) red luminescence under UV excitation.
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TODOROKI, Shin-ichi
Email: TODOROKI.Shin-ichi@nims.go.jp
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LI, Jiguang
Interest：Inorganic optical materials
Outline：Phosphors and transparent ceramics are optically functional materials that are finding wide applications in LED lighting, display, solid state lasers, and scintillation. The current advances in the above technological fields are imposing a strong need for new materials and fabrication technologies to achieve cost reduction and improved/novel optical properties.
Features：Through rational design of precursors and synthesis technologies, highly sinterable ceramics powders that can be fully densified at significantly reduced temperatures can be produced Through morphology control of the crystallites (size/shape/exposed facets), improved/novel luminescence properties can be attained Through polyhedron design of the activator ion and composition/structure design of the host lattice, high performance new phosphors can be expected.
Feasible study:
The top Figure shows multicolor emitting (Gd,Ln)3(Al,M1/M2)5O12:R3+ phosphors, where Ln is a lanthanide element, M1 and M2 are 2+ and 4+ charged dopant ions, respectively, and RE3+ is an activator ion. The compounds were derived by modifying the Gd and Al sites of Gd3Al5O12 garnet (GAG), and such a strategy not only stabilized the metastable lattice of GAG but also produced multicolor luminescence by doping different types of activators.The bottom Figure shows the (Y,Gd)2O3:Eu3+ transparent ceramics, which were fabricated via vacuum sintering at only 1700 °C for 4 h but are as transparent as the corresponding single crystals. The oxide powders used for sintering were obtained by engineering of layered hydroxide nanosheets, including composition design and thickness control, followed by proper calcination. The derived oxide particles showed high dispersion, high specific surface area and unimodal size distribution, revealing the significant advantages of the synthesis technology.
Summary：The ultimate goal of research is to develop advanced phosphors and transparent ceramics for application in the important fields of lighting/display, solid laser and scintillation (imaging), which is largely based on controllable processing of powders and rational design of chemical composition and crystal structure of the materials.
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VASYLKIV, Oleg
Email: Oleg.VASYLKIV@nims.go.jp
Interest：Deformation-resistant multipurpose ultra-hight temperature ceramics
Outline：We are currently conducting research in the chemical structural engineering of deformation-resistant UHTC carbides, borides, nitrides, and composites with ultra-hardness and ultra-high strength. We have combined the merits of powder synthesis and electric current activated sintering technique for the design of techniques applied on powder body with establishing morpho-structural and compositional features, which lead to the fabrication of bulk ceramics with superior characteristics.
Features：
- multipurpose deformation-resistant UHTC carbides, borides, nitrides and composites
- sufficient balance between ultra-high hardness, ultra-strength, toughness and modulus
- morpho-structural and compositional features with superior characteristics.
- gas turbine operation in a combined cycle power plants
Feasible study：Deformation-resistant UHTC high-entropy ceramics and composites becoming extremely attractive. Light, ultra-hard bulk B4C-based composites with hierarchical superstructure with deformation resistivity from RT to 2000°C (Fig. 1(a)) exhibit change in the deformation mechanism from brittle fracture to plastic deformation, and flexural strength far exceeding 1000MPa at 1800 - 2000°C (Fig. 1(b, c)). Depending on the loading rate, B4C-based ceramic showed 1000 - 8400MPa strength at 2000°C (Fig. 1(b)). Bulk ultrastrong TiB2-B4C ceramic exhibits a mean flexural strength of 1000MPa up to 1800°C, and further increasing to 1760MPa at 2000°C. Recently produced bulk, ultrahard, tough, deformation-resistant Ta diboride, Ta monoboride, Zr-Ta multiboride, and high-entropy TaB2-ZrB2-TiB2-HfB2.
Summary：The request for new multipurpose deformation-resistant ultra-high temperature ceramics (UHTC), able to act as special engine and vehicle protection, ceramic segmented leading edge components for aerospace, plasma-facing, ceramic parts for solar towers used for gas turbine operation in a combined cycle power plants (grids, superheaters, reheaters, evaporators, steam turbines, condensers, and chimneys) cause the worldwide demand in a new class of ceramic composites of incredible high strength, the sufficient balance between high toughness, hardness, and high-modulus.
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