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The effects of nitride (AlN, BN, TiN) addition on the electrical, thermal, and mechanical properties of porous SiC-nitride composites were investigated within a porosity range of 40–74 %. The electrical conductivity was predominantly controlled by chemistry rather than porosity, whereas the thermal conductivity was more susceptible to changes in porosity. These results suggest that the electrical conductivity of porous SiC ceramics can be tuned independently from the thermal conductivity by nitride addition. At constant thermal conductivity (∼5 Wm−1 K-1), the electrical conductivity of the baseline specimen (6.3 × 10-3 Ω-1 cm-1) could be: (1) increased by an order of magnitude (8.3 × 10-2 Ω-1 cm-1) by adding AlN and (2) decreased by an order of magnitude (7.0 × 10-4 Ω-1 cm-1) by adding BN. Typical electrical conductivity and thermal conductivity values of the porous SiC-10 vol% TiN composite were 5.3 × 10-1 Ω-1 cm-1 and ∼14.0 Wm−1 K-1, respectively, at 51 % porosity.

The properties of porous SiC ceramics were investigated as a function of Si/C content. The addition of C to SiC decreased the electrical resistivity, thermal conductivity, and compressive strength of the porous SiC ceramics for an increase in C content from 0 to 50 wt%. In contrast, the addition of Si to SiC increased both electrical resistivity and compressive strength and decreased thermal conductivity for an increase in Si content from 0 to 30 wt%. The addition of 5 wt% C increased the electrical conductivity, compressive strength, and thermal conductivity of porous SiC ceramics because of the partial densification of SiC by the removal of silica via carbothermal reduction. The current results suggest that both the electrical and thermal conductivities of porous SiC ceramics can be adjusted in the range of 9.0 × 10−2 –3.9 × 101 Ω cm and 1.3–31.4 W/(m·K), respectively, by controlling the Si or C content.

SiC-4 vol% BN composites were hot-pressed at 2050°C for 4 h at 40 MPa in a N2 atmosphere using micron-sized β-SiC and h-BN starting powders with 1 vol% sintering additives. Four batches were prepared using four different types of additive systems, i.e. Y2O3-Sc2O3, Yb2O3-CaO, Yb2O3-MgO, and Al2O3-AlN-Y2O3. The electrical, thermal, and mechanical properties of the SiC-4 vol% BN composites, which are primarily limited by the intrinsic weakness of h-BN and by the point defects (BC and AlSi) created by the dissolution of B and Al in the SiC lattice, were successfully tuned with the use of different additive systems. The electrical conductivity of SiC-4 vol% BN composites improved ~fivefold, i.e. from 2.6 (Ω·cm)−1 for the Al2O3-AlN-Y2O3-containing specimen to 13.9 (Ω·cm)−1 for the Y2O3-Sc2O3-containing specimen, owing to grain-growth-assisted N-doping and the elimination of Al-derived acceptors. Thermal conductivity was altered by 16% with the use of different additive systems. Fracture toughness dramatically increased from 4.3 MPa∙m1/2 in Yb2O3-CaO-containing specimens to 7.3 MPa∙m1/2 in Y2O3-Sc2O3-containing specimens. The electrical conductivity, thermal conductivity, flexural strength, and fracture toughness of SiC-4 vol% BN composite sintered with 1 vol% Y2O3-Sc2O3 were 13.9 (Ω·cm)−1, 82.0 W·m−1 K−1, 505 MPa, and 7.3 MPa∙m1/2, respectively.

The effects of porosity on the electrical and thermal conductivities of porous SiC ceramics, containing Y2O3–AlN additives, were investigated. The porosity of the porous SiC ceramic could be controlled in the range of 28–64 % by adjusting the sacrificial template (polymer microbead) content (0–30 wt%) and sintering temperature (1800–2000 °C). Both electrical and thermal conductivities of the porous SiC ceramics decreased, from 7.7 to 1.7 Ω−1 cm−1 and from 37.9 to 5.8 W/(m·K), respectively, with the increase in porosity from 30 to 63 %. The porous SiC ceramic with a coarser microstructure exhibited higher electrical and thermal conductivities than those of the ceramic with a finer microstructure at the equivalent porosity because of the smaller number of grain boundaries per unit volume. The decoupling of the electrical conductivity from the thermal conductivity was possible to some extent by adjusting the sintering temperature, i.e., microstructure, of the porous SiC ceramic.

Highly densified silicon carbide ceramics were fabricated by hot-pressing β-SiC powders with Sc2O3–Y2O3 and Al2O3–Y2O3 additives. The Sc2O3 and Al2O3 contents of the additives were varied while maintaining a constant Y2O3 content. For the same Y2O3 content (0.849 wt%), the electrical conductivity (σ) of the ceramics decreased to 2.3 × 102, 4.5 × 101, and 5.3 Ω-1 cm−1 with an increase in the Sc2O3 content to 0.259, 0.519, and 1.038 wt%, respectively. Similarly in the case of Al doping, the σ of the ceramics decreased to 1.2, 7.9 × 10−1, and 1.2 × 10−1 Ω−1 cm−1 with an increase in the Al2O3 content to 0.219, 0.437, and 0.874 wt%, respectively, at a fixed Y2O3 content of 0.967 wt%. This decrease in σ can be primarily attributed to the increase in the concentration of the deep acceptors generated by Sc or Al doping in the SiC lattice. The ScSi and AlSi acceptors compensated the NC donors, leading to a decrease in the carrier density of the ceramics. The lower σ of the Al-doped specimens than that of the Sc-doped ones can be attributed to their lower carrier mobility.

Mixing and crystallization are strongly influenced by fluid flow and kinetics in a stirred vessel. Computation fluid dynamics (CFD) simulation is a powerful tool to predict transient behaviors of s...

Silicon carbide (SiC) bicrystals were prepared by diffusion bonding, and their grain boundary was observed using scanning transmission electron microscopy. The n-type electrical conductivity of a SiC single crystal was confirmed by scanning nonlinear dielectric microscopy (SNDM). Dopant profiling of the sample by SNDM showed that the interface acted as an electrical insulator with a ~2-μm-thick carrier depletion layer. The carrier depletion layer contained a higher number of oxygen impurities than the bulk crystals due to the incorporation of oxygen from the native oxide film during diffusion bonding. Density functional theory calculations of the density of states as a function of the bandgap also supported these findings. The existence of a carrier depletion layer was also confirmed in a p-type polycrystalline SiC ceramic. These results suggest that the electrical conductivity of SiC ceramics was mostly affected by carrier depletion near the grain boundary rather than the grain boundary itself.

CoFe2O4 has been attracting attention for its ferrimagnetism applicable to spin transfer, resonance imaging, drug delivery etc. CoFe2O4 thin films were synthesized on Si(100) substrates by using a sol–gel deposition process. The CoFe2O4 specimen produced by post-annealing in air at 800 °C showed flat surface and polycrystalline grains with no secondary phase. The specimen exhibited magnetic hysteresis curve with magnetization up to 415 emu/cm3 and coercivity of 1.7 kOe. Such a large magnetization implies migration of a number of Co2+ ions from octahedral to tetrahedral sites of the spinel lattice. The distribution of Co2+ ions among tetrahedral and octahedral sites of CoFe2O4 was estimated by curve-fitting analysis on the Raman scattering spectrum of the specimen. The result suggests 30% of the Co2+ ions residing in the tetrahedral sites. The coexistence of Co2+ ions in both tetrahedral and octahedral sites of CoFe2O4 was also detectable by using Co 2p X-ray photoelectron spectroscopy.

Raman spectroscopy was used to measure the solubility of the metastable form of β-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (β-HNIW) in organic binary solvent mixtures. The distinct Raman spectra peaks of the solid, solute, solution, and solvent were investigated. Peaks that were not overlapping each other were used to develop a calibration curve. Then, linear relationships between solution concentration and Raman intensity were used to measure the solubility of β-HNIW in binary solvent mixtures during the dissolving process. The solubility of β-HNIW in binary solvent mixtures (ethyl acetate + n-hetpane, ethyl acetate + 1,1,2-trichloroethane, ethyl acetate + cyclohexane, ethyl acetate + toluene, ethyl acetate + diethyl ether, and ethyl acetate + petroleum ether) was investigated. The temperature ranged from 283.15 K to 333.15 K at atmospheric pressure. The solubility of β-HNIW in binary solvent mixtures decreases with increasing temperature. In order to correlate the solubility of β-HNIW,...

Silicon carbide (SiC) is an electrical semiconductor with a wide bandgap. Recently, highly conductive liquid-phase sintered SiC (LPS-SiC) ceramics have been developed by the successful dopi...

In this study, experimental work was carried out for the production of microsized hexanitrohexaazaisowurtzitane (HNIW) in a 500 L draft tube baffled (DTB) crystallizer. Acetone and isopropanol were...

SiC–BN composites were fabricated by conventional hot-pressing from β-SiC and h-BN nanopowders with 2 vol% yttria as a sintering additive. Electrical and thermal properties of the composites were investigated as a function of initial BN content. Owing to the nanosize of the starting powders, the grain-growth-assisted N-doping of the SiC lattice was significantly enhanced during liquid-phase sintering, yielding the highest-reported electrical conductivity of ~124 (Ω cm)−1 for a SiC–4-vol% BN composite. The typical values of electrical resistivity and thermal conductivity of the SiC–4-vol% BN composite at room temperature were 8.1 × 10−3 Ω cm and 92.4 W m−1 K−1, respectively.

Defects of cyclotrimethylene trinitramine (RDX) crystals prepared by cooling crystallization in various mixed solvents were studied. A normal RDX and a reduced sensitivity RDX were compared with recrystallized RDX crystals in terms of thermal analysis by differential scanning calorimetry, matching refractive index, scanning electron microscopy, bulk density, and gas chromatography. Activation energy was calculated by thermal analysis using Kissinger’s plot and correlated with supersaturation, bulk density, and inclusion fraction. The quality of the RDX crystallized in various solvents was examined by the activation energy, which is expressed as a function of the supersaturation. Formation of crystals with smooth and flawed faces can be interpreted by the relationship between supersaturation and activation energy, which enables discrimination between a reduced sensitivity RDX and normal RDX. In high supersaturation, nucleation of new layers occurs at the edges and corners of the crystal, and layered growth...

Highly conductive SiC-Ti2CN composites were fabricated from β-SiC and TiN powders with 10 vol% Y2O3-AlN additives via pressureless sintering. The effect of initial TiN content on the microstructure, and electrical and mechanical properties of the SiC-Ti2CN composites was investigated. It was found that all specimens could be sintered to ≥98% of the theoretical density. The electrical resistivity of the SiC-Ti2CN composites decreased with increasing initial TiN content. The SiC-Ti2CN composites prepared from 25 vol% TiN showed the highest electrical conductivity (∼1163 (Ω cm)−1) for any pressureless sintered SiC ceramics thus far. The high electrical conductivity of the composites was attributed to the in situ-synthesis of an electrically conductive Ti2CN phase and the growth of N-doped SiC grains during pressureless sintering. The flexural strength, fracture toughness, and Vickers hardness of the composite fabricated with 25 vol% TiN were 430 MPa, 4.9 MPa m1/2, and 23.1 GPa, respectively, at room temperature.

The electrical and thermal conductivities of bulk barium-added silicon oxycarbide (SiOC-Ba) ceramics are investigated. The SiOC-Ba ceramics exhibited improved electrical and thermal conductivities upon increasing the sintering temperature from 1450 °C to 1650 °C. Precipitation of graphitic carbon clusters observed by Raman spectroscopy and high-resolution transmission electron microscopy is attributed to the phase separation during the fabrication process. The increase in the electrical conductivity can be rationalized in terms of an increase in the density of the sp2 C C bonds within the carbon clusters. The increase in the thermal conductivity is mainly attributed to the formation of interconnected graphitic clusters in the SiOC matrix and SiC embedded in the clusters. The electrical and thermal conductivities of the SiOC-Ba ceramics sintered at 1650 °C are 14.0 Ω−1 cm−1 and 5.6 W/m K, respectively, at room temperature. The electrical conductivity of SiOC-Ba sintered at 1550 °C is 5.3 Ω−1 cm−1 and 7.0 Ω−1 cm−1 at 2 and 300 K, respectively.

Pressure and molecular-weight dependences of acoustic mode behaviors of polystyrene polymeric material were investigated by using Brillouin spectroscopy. The longitudinal, the transverse and the bulk sound velocities were measured over a wide pressure range from ambient pressure to more than 10 GPa for five polystyrene polymers whose molecular weight ranging from 3700 to 979200. The longitudinal and the bulk sound velocities displayed nearly the same pressure dependence for all polystyrenes indicating that the effective free volume is very similar in five polystyrene polymers despite the huge change in the molecular weight. The Poisson's ratio slightly increased with decreasing molecular weight.

Polymorphism and crystal size of 2,4,6,8,10-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW) were simultaneously controlled in drowning-out crystallization. Effect of antisolvent to solvent ratio on solubility and polymorphism was studied. Polymorph transformation, interfacial tension, maximum supersaturation, and scale-up of crystallization were investigated. To crystallize the small size of e-form HNIW, the supersaturation level was studied using the solvents isopropyl alcohol (IPA) and acetone (ACT). The polymorphic forms β and e were selected by controlling the supersaturation and mass fraction of the mixture solvent. By controlling the concentration, temperature, and solvent/anti-solvent ratio, e-form of a micron size was recrystallized. In this study, the optimal conditons to prepare 4-60 m sized e-form were established on a laboratory-scale. Based on the laboratory experiments, a commercial-scale process was performed successfully.

A polycrystalline SiC ceramic prepared by pressureless sintering of α-SiC powders with 3 vol% Al 2 O 3 -AlN-Y 2 O 3 additives in an argon atmosphere exhibited a high electrical resistivity of ~10 13 Ω cm at room temperature. X-ray diffraction revealed that the SiC ceramics consisted mainly of 6H- and 4H-SiC polytypes. Scanning electron microscopy and high resolution transmission electron microscopy investigations showed that the SiC specimen contained micron-sized grains surrounded by an amorphous Al-Y-Si-O-C-N film with a thickness of ~4.85 nm. The thick boundary film between the grains contributed to the high resistivity of the SiC ceramic.

The acoustic properties of three polystyrene polymers with different molecular weights were investigated as a function of temperature by using Brillouin light scattering. The longitudinal sound velocity showed a change in the slope, which depended on the molecular weight, at the glass transition temperature. The absorption coefficient exhibited a maximum above the glass transition temperature, and the maximum temperature became higher as the molecular weight was increased. Comparison with previous acoustic studies on polystyrene indicate that a substantial frequency dispersion caused by strong coupling between the longitudinal acoustic waves and the segmental motions exists in the high-temperature range.

SiC-Zr 2 CN composites were fabricated from β-SiC and ZrN powders with 2 vol% equimolar Y 2 O 3 -Sc 2 O 3 additives via conventional hot pressing at 2000 °C for 3 h in a nitrogen atmosphere. The electrical and thermal properties of the SiC-Zr 2 CN composites were investigated as a function of initial ZrN content. Relative densities above 98% were obtained for all samples. The electrical conductivity of Zr 2 CN composites increased continuously from 3.8 × 10 3 (Ωm) −1 to 2.3 × 10 5 (Ωm) −1 with increasing ZrN content from 0 to 35 vol%. In contrast, the thermal conductivity of the composites decreased from 200 W/mK to 81 W/mK with increasing ZrN content from 0 to 35 vol%. Typical electrical and thermal conductivity values of the SiC-Zr 2 CN composites fabricated from a SiC-10 vol% ZrN mixture were 2.6 × 10 4 (Ωm) −1 and 168 W/m K, respectively.

SiC-BN composites were fabricated by conventional hot-pressing from β-SiC and h-BN powders with 2 vol% Y 2 O 3 as a sintering additive. Electrical, mechanical, and thermal properties of SiC-BN composites were investigated as a function of the BN content in the starting materials. The addition of BN suppressed the grain growth of the SiC and triggered the β → α phase transformation of the SiC in SiC-BN composites. A minimum electrical resistivity of 3.7 × 10 −2 Ω cm was obtained for the SiC-4 vol% BN composite (SBN4). This low electrical resistivity was ascribed to N-doping in the SiC lattice, which acts as a donor for supplying electrons to the conduction band. Typical values for the electrical conductivity, fracture toughness, flexural strength, and thermal conductivity of the SBN4 at room temperature were 27 Ω −1 cm −1 , 4.1 MPa m 1/2 , 566 MPa, and 87 W/m K, respectively. The SiC-4 vol% BN composite can be electrical discharge machined to form complex shapes.

Hydrostaticity of poly(methyl methacrylate) (PMMA) loaded in a diamond anvil cell (DAC) was investigated up to ∼10 GPa under two conditions, i.e., with and without pressure-transmitting medium. When PMMA was loaded in the DAC without methanol-ethanol mixture, one of the most widely-used pressure-transmitting media, hydrostatic pressure condition was not fulfilled having a pressure gradient. However, the Brillouin frequency shift of the longitudinal acoustic mode of PMMA exhibited nearly the same pressure dependence regardless of the loading condition whether it was loaded with or without the methanol-ethanol mixture. This suggests that the equation of state (pressure-density relationship) of PMMA, which is calculated by using the Brillouin frequency shift, can be obtained reliably without any pressure medium at pressures less than the solidification pressure of the liquid.

Bulk SiC ceramics were fabricated by spark plasma sintering, and the effects of Y 2 O 3 addition on the structural and electrical properties were investigated. Raman spectroscopy revealed that SiC specimens with low Y 2 O 3 content (0.01 and 0.05 wt%) contained a graphitic phase (1580 and 2710 cm −1 ) which was insignificant for high Y 2 O 3 content (1.0 and 5.0 wt%). Carbon-rich SiC specimens exhibited p-type conduction character, while others exhibited n-type character. The p- and n-type SiC specimens had electrical resistivities around 10 −2 Ω cm but exhibited photoluminescence spectra quite different from each other. The p-type character is primarily attributable to silicon vacancies (V Si ), while the n-type character is ascribed to nitrogen substitution in carbon sites (N C ) of the zincblende lattice. The change in conduction type with yttria addition in the SiC specimen can be understood in terms of a competition between the densities of V Si and N C .

Dense SiC–Ti2CN composites were fabricated from β-SiC and 4 vol% TiN powders with 2 vol% equimolar Y2O3–RE2O3 (RE = Sm, Gd, Lu) additives by conventional hot pressing. Electrical and mechanical properties of the SiC–Ti2CN composites were investigated with a variation of sintering additive composition. Relative densities of ∼99.9% were achieved for all specimens. All specimens exhibited electrical resistivities on the order of ∼10−5 Ω m. These low electrical resistivities were attributed to heavy nitrogen doping in the SiC lattice (carrier density ∼1020 cm−3). Typical electrical resistivity, flexural strength, fracture toughness, and Vickers hardness values of the SiC–Ti2CN composite sintered with 2 vol% Y2O3–Lu2O3 additives were 2.2 × 10−5 Ω m, 722 MPa, 4.6 MPa m1/2, and 25 GPa, respectively.

The effects of the polytype of SiC starting powders on the thermal, electrical, and mechanical properties of pressureless sintered SiC ceramics with a new additive system (6.5 vol% Y2O3-Sc2O3-AlN) were investigated. Powder mixtures prepared from α- or β-SiC powders were sintered at 1950 °C for 6 h in a nitrogen atmosphere without an applied pressure. We found that both specimens could be sintered to >96% of the theoretical density without an applied pressure. The SiC ceramic fabricated from β-SiC powders showed lower electrical resistivity, higher thermal conductivity, and better mechanical properties than that from α-SiC powders. The flexural strength, fracture toughness, hardness, electrical resistivity and thermal conductivity values of the SiC ceramics fabricated from β-SiC powders were 520 MPa, 5.1 MPa m1/2, 25.0 GPa, 6.7 × 10−1 Ω cm and 110 Wm−1 K−1 at room temperature, respectively. The new additive system achieved the highest thermal conductivity in pressureless liquid-phase sintered SiC ceramics.

The effects of carbon addition on the electrical properties of silicon-oxycarbide (SiOC) ceramics were investigated. The electrical resistivity of the dense bulk SiOC specimen decreased gradually from 4.9 × 10−1 Ω cm to 4.5 × 10−2 Ω cm with increasing carbon content from 0 to 16 wt% at room temperature. Raman spectroscopy investigation revealed the existence of a graphite phase characterized by a carbon-carbon sp2-bond with increasing density with increasing C content in the SiOC specimen. The decrease in electrical resistivity with increasing C content can be explained in terms of an increase in the density of conductive sp2-bonds promoted by carbon precipitation in an amorphous SiOC matrix. The resistivities of the SiOC specimens exhibited slow increases with decreasing temperature in the 2–300 K range, the slowest one (16 wt% C) being 4.5 × 10−2 Ω cm (300 K) and 5.2 × 10−2 Ω cm (2 K).

This study examines the synthesis of SiC whisker on graphite felt through the non-catalytic VS CVD (Vapor Solid Chemical Vaporized Deposition) mechanism in order to investigate its potential as a filter to replace the conventional DPF (Diesel Particulate Filer). Since the CVD process is conducted mostly in high temperature exceeding 1000 °C, many restrictions exist in selecting the substrate. Graphite felt is a filter form of non-woven fabric. The graphite felt was selected as a suitable substrate material for this study based on the VS CVD mechanism due to its relatively low cost, high heat resistance, and high flexibility. The appropriate SiC whisker structure of the nanoscale was grown on the graphite felt that exhibited the fore-mentioned characteristics. This enhanced the filtration performance of the bare graphite felt filter more than two times without compromising the gas permeability. Additionally, thermal oxidation resistance was elevated by at least 200 °C more than the bare graphite felt, thereby indicating the transfer of a part of the desirable chemical properties of the SiC.

The elastic properties of a biocompatible silk film were investigated under temperature and pressure variations by using Brillouin spectroscopy. The Brillouin frequency shift decreased monotonically upon heating and showed a sudden change at the glass transition temperature. The existence of water molecules in the film increased the longitudinal modulus by approximately 10% and induced a relaxation peak in the hypersonic damping at ~60 ◦ C. The pressure dependences of the sound velocities of the longitudinal and the transverse acoustic modes and the refractive index were determined for the first time at pressures up to ~15.5 GPa. All these properties increased upon compression; these changes indicated that the free volume in the silk film collapsed at a pressure of about 3 GPa.

Co-doped lithium manganese oxide (LiCo x Mn 2-x O 4 ) cathodes were prepared as thin films via a sol-gel process to investigate the effects of the octahedral Co substitution on electrochemical properties. X-ray diffraction and scanning electron microscopy results showed that the polycrystalline films (x ≤ 0.3) were composed of phase-pure grains with the sizes distributed mainly in 100–200 nm range. The cubic lattice parameters of the spinel LiCo x Mn 2-x O 4 samples decreased gradually with increasing Co composition. X-ray photoelectron spectroscopy data indicated that cobalt ions in LiCo x Mn 2-x O 4 exist as Co 3+ mostly. The electrochemical investigations of LiCo x Mn 2-x O 4 cathodes include cyclic voltammetry, cycling performance, charge-discharge profile, and rate capability in the 3.5–4.3 V potential range. The x = 0.05 cathode exhibited initial discharge capacity close to that of LiMn 2 O 4 cathode and less capacity fading than LiMn 2 O 4 after extended charge-discharge cycles (>200). The x = 0.1 cathode exhibited a reduction in initial discharge capacity by ∼10% but the capacity was retained up to ∼300 cycles. The improved capacity retention of LiCo x Mn 2-x O 4 cathodes is attributable to the improved structural stability by octahedral Co 3+ substitution for suppressing Mn 3+ -related Jahn-Teller distortion and cathode dissolution into electrolyte.

Cocrystals of salicylic acid (derived from reaction between aspirin and coformers) with 4,4′dipyridyl, nicotinamide, isonicotinamide, N,N′-diacetylpiperazine and piperazine have been examined with intent to improve physicochemical properties of antipyretic agent. All of the resulting cocrystals, salicylic acid/4,4′dipyridyl (2:1), salicylic acid/nicotinamide (1:1), salicylic acid/isonicotinamide (1:1), salicylic acid/piperazine (1:0.5) and salicylic acid/ N,N′-diacetylpiperazine (2:1) (derived from reaction between aspirin and piperazine) are obtained solution cooling/evaporation experiments. The structural analysis has shown that the well-known COOH⋅⋅⋅N heterosynthon was considered the key element in the cocrystals design strategy. The carboxylic acid⋅⋅⋅pyridine hydrogen bond is an often used supramolecular synthon. The results from X-ray Powder Diffraction, DSC, Raman and single-crystal X-ray analysis revealed the formation of cocrystal of salicylic acid with several coformers.

The effect of grain growth on electrical properties of SiC ceramics sintered with a new additive system (Gd2O3–Y2O3) was investigated. Hot-pressing of β-SiC with 3 vol% Gd2O3–Y2O3 in a nitrogen atmosphere resulted in highly conductive SiC ceramics (∼10−2–10−3 Ω cm), whereas hot-pressing of the same specimen in an argon atmosphere resulted in semi-insulating SiC ceramics (∼108 Ω cm). This difference was due to the nitrogen (N) doping in SiC ceramics in the former case. The N-doping in SiC ceramics was achieved by grain growth of SiC grains via a solution-reprecipitation mechanism. The electrical resistivity of N-doped SiC ceramics decreased with an increase in grain size of SiC ceramics if there is no β → α phase transformation of SiC. The lowest electrical resistivity obtained was 8.9 × 10−3 Ω cm after 6 h sintering at 2000 °C under an applied pressure of 40 MPa in nitrogen.

Acoustic properties of glycerol was investigated in a wide pressure range from ambient pressure to 30.9 GPa by using a multi-pass Fabry–Perot interferometer and a diamond anvil cell. Pressure dependences of the sound velocity and the Brillouin linewidth showed substantial changes at low pressures below ~4 GPa. This was attributed to the coupling between the main structural relaxation process and the longitudinal acoustic waves. The pressure dependence of the refractive index and the density of glycerol could be obtained by using two scattering geometries and the Lorentz–Lorenz relation.

Composites of SiC–BN consisting of uniformly distributed plate-shaped hexagonal BN grains and nitrogen-doped α-SiC grains were fabricated by conventional hot-pressing in an argon atmosphere without sintering additives. The effects of the BN content on the electrical, structural, thermal, and mechanical properties of the SiC–BN composites were investigated. The electrical resistivity showed a minimum at a BN content of 10 vol%, which is attributable to N substitution for C sites in the 6H–SiC lattice, which acts as donors for supplying carriers to the conduction band. The thermal conductivity of the composites showed a decreasing trend with increasing BN content, indicating that the presence of the SiC/BN interface discourages phonon conduction in the composites. The electrical resistivity, thermal conductivity, flexural strength, fracture toughness, and hardness of the SiC–10 vol% BN composite were 9.3 × 105 Ω × cm, 74.4 W/m K, 559 MPa, 3.6 MPa m1/2, and 23 GPa, respectively.

We applied high-pressure Brillouin light spectroscopy to study the mechanical properties of representative amorphous polymers: polyetherimide (PEI), polyethersulfone (PES), and unplasticized polyvinylchloride (PVC). The pressure dependence of optical and elastic properties such as refractive indices and acoustic phonon velocities was obtained by employing both a forward, symmetric scattering and a backscattering geometry up to ~11 GPa. While PEI and PES showed longitudinal and transverse acoustic phonon modes simultaneously at above a certain pressure, PVC showed only one longitudinal acoustic phonon mode, which limited the access to further information. For PEI, PES, and PVC films, we successfully calculated pressure-dependent Poisson's ratios, bulk moduli, shear moduli, Young's moduli, and density-pressure isotherms. Furthermore, by using the Lorentz-Lorenz equation, we corroborated the conventional assumption that the mean polarizability of polymeric materials is nearly constant even when pressure is applied.