Yoshio Sakka

National Institute for Materials Science | NIMS · Materials Processing Unit

Nanocomposites with nanoparticles dispersed as the second phase have been reported to have improved mechanical properties. In spite of this potential processing methods to produce these nanocomposites are not well established. In this study, Al2O3/mullite/SiC nanocomposites were prepared by the reaction sintering of green compacts prepared by slip...

In order to clarify the orientation dependent deformation behavior of the MAX phase ceramics, compressive deformation behavior was examined in a textured Ti3SiC2 (TSC) at a high temperature of 1200°C. Depending on the relationship between the texture and loading directions, both the deformation behavior and microstructure were strongly influenced,...

In order to clarify plastic deformation behavior and mechanism of fracture energy absorption of Ti3SiC2, Vickers indentation tests were conducted for Ti3SiC2 sintered bodies with various textured orientations. Textured Ti3SiC2 sintered bodies were fabricated by slip casting in a strong magnetic field and spark plasma sintering (SPS), and their orie...

To clarify the effect of constraint conditions on the kink formation, fabrication process of the texture and porosity controlled Ti3SiC2 polycrystals was investigated and microstructural evolution during high temperature deformation was examined in it under high temperature uniaxial compression tests at 1200°C. Dense textured Ti3SiC2 sintered body...

A green chemical precipitation route was used to yield a hydrated basic sulfate precursor upon calcination at 1000°C into a series of (Y,Gd)2O2SO4:Dy particles. The phosphors exhibited characteristic Dy3+ emissions from 4F9/2→6HJ (J = 15/2, 13/2, 11/2) transitions under ultraviolet light excitation; the quenching concentration of Dy3+ was determine...

To clarify the effect of constraint conditions on the kink formation, fabrication process of the texture and porosity controlled Ti3SiC2 polycrystals was investigated and microstructural evolution during high temperature deformation was examined in it under high temperature uniaxial compression tests at 1200℃. Dense textured Ti3SiC2 sintered body w...

A series of (Lu0.99‐x Er0.01Yb x )2O3 and (Lu0.99‐x Er0.01Yb x )2O2S (x = 0‐0.1) phosphor particles were prepared to investigate their upconversion luminescence properties. Under 980 nm pumping laser, the two phosphors both exhibit strong green emission at ∼520‐573 nm and weak red emission at ∼648‐688 nm arising from ⁴S3/2/²H11/2→⁴I15/2 and ⁴F9/2→⁴...

Lanthanum silicate oxyapatite (LSO) has a very high oxide-ion conductivity along the c-axis of its hexagonal crystal. The effect of the crystal orientation in LSO ceramics on the anisotropy of their electrical and mechanical properties has not been studied systematically because centimeter-scale ceramics with different degrees of crystal orientatio...

Amorphous bimetallic borides are an emerging class of catalytic nanomaterial that has demonstrated excellent catalytic performance due to its glass-like structure, abundant unsaturated active sites, and synergistic electronic effects. However, the creation of mesoporous Earth-abundant bimetallic metal borides with tunable metal proportion remains a...

Porous metallic aerogels are a new class of cutting-edge materials useful in catalysis because they combine high conductivity with low density and high surface area. However, the exploration of transition metal-based aerogels with core-shell architectures remains a fundamental challenge. Here, we report a one-step auto-programmed synthesis method t...

Supplementary Information for D. Demirskyi, T. Nishimura, T.S. Suzuki, Y. Sakka, O. Vasylkiv & K. Yoshimi (2020): High-temperature toughening in ternary medium-entropy (Ta1/3Ti1/3Zr1/3)C carbide consolidated using spark-plasma sintering, Journal of Asian Ceramic Societies, https://doi.org/10.1080/21870764.2020.1840703

In order to clarify plastic deformation behavior and mechanism of fracture energy absorption of Ti3SiC2, Vickers indentation tests were conducted for Ti3SiC2 sintered bodies with various textured orientations. Textured Ti3SiC2 sintered bodies were fabricated by slip casting in a strong magnetic field and spark plasma sintering (SPS), and their orie...

The elastic properties of a single-crystalline Ti3SiC2 MAX phase with a nanolayered crystal structure, comprising Ti-Si and two distinct Ti-C bonding layers, that had remained unclear because of the difficulty in growing large single crystals, were studied. Rather than unavailable large single crystals, polycrystalline samples with a crystallograph...

We report for the first time the effect of temperature on the mechanical properties of (Ta1/3Ti1/3Zr1/3)C carbide. Flexural strength and fracture toughness were investigated using the three-point bending technique in argon. Using commercially available carbide powders with an equimolar ratio and performing spark plasma consolidation at 1973°C, we o...

The aerosol gas deposition (AGD) is a low temperature method for film formation. No heating procedure exists in the AGD process during the formation of the AGD films, where even ceramic films can be fabricated. We have demonstrated the advanced AGD with the practical application of a room temperature film-forming device for ceramics that can form a...

Generating high surface area mesoporous transition metal boride is challenging but interesting because incorporation of boron atoms can generate lattice distortion to form amorphous metal boride which shows unique properties in catalysis. Here we report the first synthesis of mesoporous cobalt boron amorphous alloy colloidal particles using soft te...

The solid solution formation and consolidation of the (Ta,Zr,Nb)C single-phase ceramic made from commercial TaC, ZrC and NbC powders prepared by spark plasma sintering at the temperature of 1920 °C was investigated. Phase analysis and lattice parameter measurements by X-ray diffraction showed multi-stage formation of the single-phase high-entropy-t...

In the current review paper, we provide the experimental evidences for the controlled structure of diamond cubic silicon nanocrystals (SiNCs) which enhances their photoluminescence quantum yields (PLQYs). Hydrogen-terminated Si provides a basic surface for further modification. Their enhancement was performed by a simple ligand exchange between the...

Reinforcement of ceramic composites using carbon nanotubes (CNT) has been extensively studied for materials such as Al2O3, Si3N4 and tetragonal ZrO2. Knowledge concerning CNT composites based on a matrix of cubic zirconia (8YZ) is in short supply, however. This paper presents a study on the addition of 1 wt% CNT to an 8YZ matrix. CNT was functional...

Polycrystalline transparent magneto-optical Ho2O3 ceramics were successfully fabricated by vacuum sintering using the self-reactive resultant HoOF as a sintering aid. They had an in-line transmittance of 72.0% at 1550 nm and the wavelength-dependent Verdet constants of -182±8, -46±3, and -22±2 rad/Tm at 633, 1064 and 1550 nm (approximately 1.3 time...

High‐optical‐quality ternary [(Y1‐xGdx)0.99Dy0.01]2O3 (x=0 and 0.4) ceramics were successfully fabricated by vacuum sintering with in‐line transmittances of 71.4‐75.1% at 574 nm, the wavelength of Dy3+ emission (the 4F9/2 → 6H13/2 transition). Substitution of Gd3+ for Y3+ significantly affected the photoluminescent and scintillant properties of the...

Ceramics with highly controlled microstructures at all levels from micrometer to nanometer order are required to improve their properties. To realize such ceramics, advances in powder processing are indispensable. Powder processing involves the preparation of fine particles, surface modification, consolidation, and sintering. The colloidal processi...

Electric current activated/assisted sintering (ECAS) is a growing class of versatile techniques for sintering particulate materials. Nowadays, most of the scientific attention is focused on pulsed electric current sintering known as spark plasma sintering (SPS). SPS has been successfully applied to electrically conductive and low-electrical-conduct...

Spark plasma sintering (SPS), which can precisely control such sintering conditions as temperature, heating rate, the extent of uniaxial loading, and the holding time under a vacuum, has great potential for fabricating various types of functional materials. In particular, the high densification rates attained by this technique enable suppressed gra...

Here we show an electrophoretic deposition process for a uniform coating of glass substrate surface with fluorescent silicon nanocrystals (SiNCs). The NCs with ∼35% of photoluminescence quantum yields (PLQYs) were synthesized by thermal disproportionation of hydrogen silsesquioxane, followed by hydrosilylation of 1-decence. Next, the hollow-silica...

In ceramic forming techniques high particles packing can provide better properties of the final ceramic products. The high quality of the material coupled with the shape complexity of the ceramic product is still challenging. The aim of this work was the optimization and preparation of the ceramic samples based on two alumina powders of different p...

β‐sialon:Eu²⁺ phosphor particles were successfully coated by TiO2 nanoparticles via the sol‐gel method. The TiO2‐coated β‐sialon:Eu²⁺ phosphor had a significantly improved photoluminescence (PL) performance under the 365 nm excitation, due to the localized surface plasmon resonance (LSPR) at the interface between the TiO2 coating layer and phosphor...

To add new functions and improve the performance of advanced ceramics, highly controlled microstructure is required. The microstructure control of the hierachical, graded, laminated, or oriented microstructures at all levels from micrometer to nanometer order is a well-known example. To satisfy the requirements, advances in powder processing are in...

Ti3SiC2 is a typical Mn+1AXn (MAX) phase ceramic and exhibits both metal-like and ceramic-like properties. To improve these properties, texturing and Al2O3 addition were performed. The commercial Ti3SiC2 powder used contained approximately 10 mass% TiC phase. Textured Ti3SiC2 was prepared by slip casting in a strong magnetic field (MF) followed by...

Although yttria-stabilized zirconia (YSZ) is prevalent as ceramic electrolyte in solid oxide fuel cells (SOFCs), a trend to switch to lower operating temperatures requires the replacement of YSZ. Lanthanum silicate oxyapatite (LSO) is one of encouraging materials for satisfying this requirement. The design of SOFCs and SOFC stacks demands the knowl...

Oxidation resistance of textured Ti3AlC2 ceramics was measured in the temperature range 1273–1573 K. It was found that the oxidation was markedly anisotropic and the samples exhibited a better oxidation resistance when tested along a direction transverse to the c-axis. This behavior was attributed to the rapid diffusion of Al within its basal plane...

Here we show an electrophoretic deposition process for a uniform coating of glass substrate surface with fluorescent silicon nanocrystals (SiNCs). The NCs with ~35% of photoluminescence quantum yields (PLQYs) were synthesized by thermal disproportionation of hydrogen silsesquioxane, followed by hydrosilylation of 1-decence. Next, the hollow-silica...

The high-temperature phase of lanthanum germanate is useful due to its high oxide ion conductivity. While the transition from the high- to low-temperature phase could be suppressed by yttrium substitution in lanthanum sites, full stabilization of the high-temperature phase was difficult to achieve by yttrium substitution under conditions of differe...

The surface modification on the β-sialon:Eu²⁺ phosphor particles was successfully achieved by the SiO2 coating via a sol-gel method. The photoluminescence (PL) intensity of the phosphor was effectively enhanced and dominantly depending on the homogeneity of the SiO2 coating. It was found that more homogeneous and smooth SiO2 coating was responsible...

The development of inversion domain networks consisting of basal-plane and pyramidal-plane inversion domain boundary (b-IDB and p-IDB) interfaces within grains in Sn-Al dual-doped ZnO (Zn0.98Sn0.01Al0.01O) polycrystalline ceramics has been confirmed using transmission electron microscopy. The atomic structure of the b-IDB and p-IDB interfaces has b...

Lanthanum silicate oxyapatite (LSO) is a promising ion conductive ceramic material, which has higher oxygen ion conductivity at intermediate temperatures (600-800°C) compared to yttria-stabilized zirconia. Its mechanical properties, though important for any of its applications, have been scarcely reported. In this study, we compare apparent densifi...

Carbon contamination during the SPS processing was investigated in the spinel, alumina and zirconia. The carbon contamination changes with the SPS conditions and the target materials. At the high heating rate of 100. °C/min, the contamination occurred over the entire area in the spinel, but only around the surface areas in the alumina and zirconia....

Highly transparent hydroxyapatite ceramics were fabricated by using the electrically conductive SiC mold during spark plasma sintering. Compared to the conventional graphite mold, the SiC mold lowered the sintering temperature by 50°C at least. The in-line transmission of the sintered ceramics is 82% at a wavelength of 600 nm. The high transmission...

In this study, we report that the deposition rate of films is indicated to be strongly related to the preheating conditions of source powder mixture of ZrO2 and NiO. A stable luminescence was observed clearly during film fabrication. In an aerosol gas deposition method, the source powder is charged during transport by the mutual friction of particl...

Ti3SiC2 is a typical Mn+1AXn (MAX) phase ceramics and shows unique metallic-like and ceramic-like properties. To improve these properties, texturing and Al2O3 addition have been conducted. The commercial Ti3SiC2 powder used contains approximately 10 wt% TiC phase. Textured Ti3SiC2 was prepared by slip cast in strong magnetic fields followed by spar...

For attaining high-strain-rate superplasticity (HSRS) in ceramic materials, prerequisites are described on the basis of existing knowledge about high-temperature plastic deformation and intergranular cavitation mechanisms. The knowledge suggests that a combination of grain-size refinement to 100-200 nm or smaller and enhanced diffusion caused by do...

We present a study of sulfonitric treatment and its effect on MWCNTs at different temperatures (90, 110, 130 and 150°C) using DRX, XPS, FTIR, Raman spectroscopy, TEM and zeta potential. It was found that oxidation starts with the C-C and C-H bonds generating different oxidized groups from alcohol to carboxylic acid, following a sequential oxidation...

This is the first comprehensive review on inherent anisotropic features of transition metal diboride (MB2) and their implementation for tailoring the microstructure and properties of MB2-based Ultra-high temperature Ceramics (UHTCs). The emphasis is on the processing approaches, microstructures, and properties of self-reinforced and/or textured MB2...

Conventional ceramic processing techniques do not produce ultrafine grained materials. However, since the mechanical and optical properties are highly dependent on the grain size, advanced processing techniques are needed to obtain ceramics with a grain size smaller than the wavelength of visible light for new laser sources. As an empirical study f...

Carbon contamination from the carbon paper/dies during spark-plasma-sintering (SPS) processing was examined in the MgAl2O4 spinel. The carbon contamination sensitively changes with the heating rate during the SPS processing. At the high heating rate of 100°C/min, the carbon contamination having organized structures occurred over almost the entire a...

Capture movie of the actual procedure for the R//CPE connected model in the J. Ceram. Soc. Jpn., 124, 945-949 (2016).

Capture movie of the actual procedure for the R//C connected model in the J. Ceram. Soc. Jpn., 124, 945-949 (2016).

Submicron-sized particles of vaterite, containing carbamate-functionalised siloxane (V–Si), were prepared as the precipitant of radioactive strontium in the treatment of wastewater. The particles consisted of 10–22 nm-sized vaterite crystallites with preferred-orientation towards (00l) plane; a highly charged plane. The crystallites were suggested...

Hexagonal (Gd0.95RE0.05)PO4·nH2O nanowires ~300 nm in length and ~10 nm in diameter have been converted from (Gd0.95RE0.05)2(OH)5NO3·nH2O nanosheets (RE = Eu, Tb) in the presence of monoammonium phosphate (NH4H2PO4) and ethylene diamine tetraacetic acid (EDTA). They were characterized by X-ray diffraction, thermogravimetry, electron microscopy, and...

Bulk niobium diboride ceramics were consolidated by spark plasma sintering (SPS) at 1900°C. SPS resulted in dense specimens with a density of 98% of the theoretical density and a mean grain size of 6 μm. During the SPS consolidation, the hexagonal boron nitride (h-BN) was formed from B2O3 on the powder particle surface and residual adsorbed nitroge...

Tribological property of c-axis textured shell-like Ti3AlC2 ceramic was investigated using reciprocating sliding balls (SUS304) under loads of 1, 5, and 9 N. It was found that the textured top surface (TTS), corresponding to the (000l) plane, shows the lowest mean coefficient of friction in comparison with those measured on the textured side surfac...

TiO2/reduced graphene oxide (rGO) nanocomposites were prepared via a facile one-step hydrothermal method using TiCl3 as the TiO2 precursor. Cetyltrimethyl ammonium bromide (CTAB) was introduced as a stabilizer for GO in solution. The effects of GO content, Ti³⁺ concentration and urea additive on phase constituent and morphology of the TiO2 crystall...

The atomic and electronic structures of inversion domain boundaries in Mn-Al dual-doped ZnO (Zn0.89Mn0.1Al0.01O) have been investigated. Using atomic-resolution scanning transmission electron microscopy, a head-to-head c-axis configuration and cation stacking sequence of αβαβ|γ|αβαβ along the c-axis were observed at the basal-plane inversion domain...

A large amount of multi-walled carbon nanotubes (MWCNTs) (10 vol%) were uniformly and intimately dispersed within ZrB2 ceramic matrix using an aqueous hetero-coagulation approach followed by spark plasma sintering (SPS) at 1700 °C. Addition of MWCNTs inhibited grain growth, increased the relative density from 89% to 97%, and resulted in a composite...

Siloxane-containing vaterite (SiV) microparticles were prepared with controlling the degree of aminopropyl-functionalization in the siloxane; they are aiming for applications as bone regenerative devices. The aim of this work was to evaluate the structure at siloxane/vaterite interphase and to control the solubility of particles by the structural t...

(Tb1-xCex)3Al5O12 yellow phosphors (0≤x≤0.05) were calcined from their coprecipitated carbonate precursors, and the effects of the temperature and atmosphere (air and H2) of calcination on the sequence of phase evolution and the characteristics of the powders were investigated in detail. The activation energy for the crystallite growth during calci...

The synthesis of a layered Ln2(OH)4SO4·nH2O material (Ln-241) with a smaller lanthanide ion (Dy³⁺) was successfully achieved through the optimization of the hydrothermal conditions, and the effect of lanthanide contraction on the chemical composition, phase structure, and crystallite/particle morphology of the products was investigated and discusse...

Fully dense transparent alumina is obtained after spark plasma sintering at 1000°C by using the electrically conductive SiC molding set. Compared to the conventional graphite set, the new mold material lowered the sintering temperature by 150°C for full densification. The SiC set has a lower electrical conductivity than that of the graphite set, wh...

Effects of the ceramic powder size used for suspension as well as several processing parameters in suspension plasma spraying of YSZ were investigated experimentally, aiming to fabricate highly segmented microstructures for thermal barrier coating (TBC) applications. Particle image velocimetry (PIV) was used to observe the atomization process and t...

This study develops a fabrication technique to obtain Fe-free and Fe-bearing (Fe:Mg = 1:9) olivine aggregates not only with high density and fine grain size but with crystallographic preferred orientation (CPO). A magnetic field (≤12 T) is applied to synthetic, fine-grained (~120 nm), olivine particles dispersed in solvent. The alignment of certain...

Ti3SiC2 is a typical Mn+1AXn (MAX) phase ceramics and shows unique metallic-like and ceramic-like properties. To improve these properties, texturing and oxide addition have been conducted. Textured Ti3SiC2 and 10 vol% Al2O3/Ti3SiC2 were prepared by slip cast in strong magnetic fields followed by SPS at 1350°C. The Lotgering orientation factor of te...

We briefly review our recent works on addressing the dispersion obstacle of carbon nanotubes (CNTs) in a ceramic material and on the in situ characterization of the direct reinforcing mechanism and properties of multi-walled CNTs when intimately embedded in a ceramic matrix. In particular, we discuss the new reinforcing mechanism at the nanoscale r...

Solid solution of Gallo-titanogallate type KxGa8Ga8+xSn16-xO56 (1.2 ≤ x ≤ 1.6) and Hollandite type K2Ga2Sn6O16 were prepared by the solid state reaction method. Then, the most suitable process for obtaining dense sintered body was studied by conventional heat-treatment of uniaxial pressed pellet, hot isostatic pressing (HIP) and spark plasma sinter...

A new program for electrochemical impedance analysis has been developed based on the expanded measurement model. The main feature of this program is that it allows the user to easily estimate the equivalent circuit, as well as an initial guess of the fitting parameters, through a graphic user interface (GUI). The function to illustrate the partial...

Lanthanum silicate oxyapatite ((LSO, La9.33+2x(SiO4)6O2+3x)(0<x<0.33)) is an oxygen-ion conductor that offers some advantages over the typical yttria-stabilized zirconia (YSZ) used in SOFCs. LSO has higher oxygen-ion conductivity than YSZ at temperatures below 873K.The powder was synthesized from reagent grade La2O3 and SiO2 powders. Presents an av...

Introduction Kramers-Kronig (KK) transform test is well known to check the linearity, causality, and stability of measured impedance spectrum. ¹⁾ By contrast, satisfaction of the KK transform indicates that the measured impedance spectrum can be reproduced by adequate equivalent electrical circuit using lumped parameter elements. Although the conve...

【Introduction】 Lanthanum silicate oxyapatite (LSO) has attracted attention as a new solid electrolyte for solid oxide fuel cell due to its high oxygen-ion conductivity and chemical stability [1] . Magnesium oxide has been reported as the effective dopant to improve the oxygen-ion conductivity of the LSO [2] . It has been revealed that non-doped LSO...

Sn-Al co-doped polycrystalline ZnO ceramics were prepared by sintering in air. Phase and microstructure analysis was performed by X-ray diffraction and SEM-EDS and thermoelectric properties were measured. XRD analysis showed a ZnO primary phase as well as secondary phase peaks due to the formation of a Zn2SnO4 spinel phase or SnO2(ZnO:Sn-Al)m inter...