Submicron-size SiC ceramics were sintered to densities >97% of the theoretical density by adding 5 wt % in situ-synthesized nano-size SiC and 2 wt % AlNRE 2 O 3 (RE = Y, Er). The SiC ceramics showed very low electrical resistivity in an order of 10 ¹4 ³·m. This low electrical resistivity was attributed to the smaller amount (2 wt %) of sintering additives addition and their microstructural characteristics, i.e., growth of nitrogn-doped SiC grains and the confinment of non-conducting Y-and Er-containing phases in the junction areas.©2011 The Ceramic Society of Japan. All rights reserved.Key-words : SiC, Sintering, Electrical resistivity [Received June 15, 2011; Accepted September 20, 2011] Silicon carbide (SiC) ceramics with a small amount of additives or without additives have attracted considerable attention for use in semiconductor processing, nuclear fusion reactors, and high temperature thermomechanical applications because of their excellent chemical and thermal stability and good mechanical properties.1)8) In the early 1980 s, Omori and Takei 9) reported an innovative approach to fully densify SiC at temperatures as low as 1850°C via liquid-phase sintering by adding rare earth oxides to the starting powder. Since this innovative work, interest in liquidphase sintered (LPS)-SiC has grown continuously, becausae LPSSiC ceramics show better mechanical properties than solid-state sintered SiC ceramics. sintered SiC ceramics with 3 wt % RE 2 O 3 AlN additives (RE = Sc, Lu, Y). SiC ceramics sintered with a smaller amount of additives would be more beneficial for applications in semiconductor processing and nuclear fusion reactors because of their better chemical and thermal stability.In this study, the sinterability of SiC ceramics with 2 wt % additives (RE 2 O 3 AlN, RE = Y, Er) was investigated with or without 5 wt % in-situ-synthesized nano-size SiC addition. The electrical resistivity of the resulting SiC ceramics was also investigated.For SiC with 2 wt % additives, submicron ¢-SiC (Ultrafine, Betarundum, Ibiden Co. Ltd.), polysiloxane (1036 kg/m 3 , GE Toshiba Silicones Co., Ltd., Tokyo, Japan), phenol resin (1090 kg/m 3 , Kangnam Chemical Co. Ltd., Incheon, Korea), Y 2 O 3 (99.9%, Kojundo Chemical Lab Co. Ltd., Sakado, Japan), Er 2 O 3 (99.9%, Kojundo Chemical Lab Co. Ltd., Sakado, Japan) and AlN (grade B, H. C. Starck, Berlin, Germany) were mixed at the weight ratio shown in Table 1 by ball milling using SiC balls and a polypropylene jar for 24 h in ethanol. The AlN:RE 2 O 3 molar ratio was 3:2. The mixtures were dried, sieved (60 mesh), pressed uniaxially and heat-treated at 200°C for 2 h in air to cross-link the polysiloxane in the mixture. The compact was heat-treated at 1450°C for 1 h and hot-pressed at 2050°C for 6 h under 40 MPa in an atmospheric pressure of nitrogen.The relative densities of the hot-pressed specimens were determined using the Archimedes method. The theoretical densities of each specimen were calculated according to the rule

Electrically and thermally conductive SiC ceramics were fabricated by hot-pressing ¢-SiC, 2 or 4 vol % TiN, and 2 vol % Y 2 O 3 powder mixtures in a nitrogen atmosphere. X-ray diffraction data indicated that the specimens consisted mostly of ¢-SiC grains and traces of ¡-SiC and Ti 2 CN clusters. Highly-conductive Ti 2 CN clusters segregated between SiC grains contributed to reduce the electrical resistivity of the TiN-doped SiC specimens. The high thermal conductivity of the TiN-doped SiC specimens was attributed to the lack of solubility of Ti and Y in the SiC lattice and the suppression of a massive ¢¼¡ phase transformation in SiC. The electrical resistivity and thermal conductivity of the SiC with 2 vol % TiN specimen were 2.4 © 10 ¹3 ³·cm and 174.1 W/m·K, respectively.

Structural transformation and the related variation in magnetic and optical properties of Co 3−x Fe x O 4 thin films grown by a sol-gel method have been investigated as the Fe composition varies up to x=2. The normal spinel phase is dominant below x=0.55 and the inverse spinel phase grows as x increases further. Conversion electron Mössbauer spectroscopy (CEMS) measurements indicate that the normal spinel phase have octahedral Fe 3+ ions mostly while the inverse spinel phase contain octahedral Fe 2+ and tetrahedral Fe 3+ ions. For higher Fe composition (x >1.22), Co 2+ ions are found to substitute the octahedral Fe 2+ sites. The measured optical absorption spectra for the Co 3−x Fe x O 4 films by spectroscopic ellipsometry support the CEMS interpretation.

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Conductive nickel-cobaltite (Ni x Co 3-x O 4 ) thin films were synthesized on Al 2 O 3 substrates by using a solgel process for varying Ni composition x (B 1.0). X-ray diffraction data indicated that the polycrystalline Ni x Co 3-x O 4 samples have cubic spinel (Fd 3m) structure with the lattice constant increasing slightly with increasing Ni composition (by 0.5 % for x = 1.0 compared to that of Co 3 O 4 ). X-ray photoelectron spectroscopy data indicated that the Ni ions in nickel-cobaltite have multi-valence (Ni 2? and Ni 3? ). The temperature-dependent electrical resistivity (q) data of the nickel-cobaltite samples were measured in the 4-300 K range in comparison with Co 3

Cr-based chalcogenide spinels, which do not have heterovalency and distortioninduced ions such as manganese oxides with perovskite structure, have demonstrated the existence of colossal magnetoresistance. In order to investigate the magnetotransport phenomena and magnetic properties of sulfospinels Zn x Fe 1−x Cr 2 S 4 , polycrystalline Zn x Fe 1−x Cr 2 S 4 samples were synthesized in the 0≤x≤0.2 range by a solid reaction method. The crystal structure for x=0.05, 0.1, and 0.2 turned out to be cubic at room temperature by X-ray diffraction measurement. In magnetoresistance measurement, Zn x Fe 1−x Cr 2 S 4 samples indicate that this system is semiconducting below about 150 K. The temperature of maximum magnetoresistance is almost consistent with Curie temperature. The isomer shift and the electric quadrupole shift of Zn x Fe 1−x Cr 2 S 4 samples by Mössbauer experiment show that Fe 2+ ions occupy the tetrahedral site in the spinel structure. As the Zn ions are substituted for Fe ions, the Jahn-Teller relaxation slows down and the electric quadrupole shift increases. The magnetotransport phenomena of Zn x Fe 1−x Cr 2 S 4 is related to Jahn-Teller effect and half-metallic electronic structure, which are different from the double exchange interactions of the manganite La-Ca-Mn-O system or the triple exchange interactions of sulfospinel Cu x Fe 1−x Cr 2 S 4 .

Porous silicon carbide ceramics were prepared from a polysiloxane, carbon black, SiC filler, sacrificial templates (co-polymer microbeads) and Al2O3-Y2O3 additives by a carbothermal reduction and subsequent sintering process. The effect of the sintering temperature on the microstructural development and structural characteristics of the porous ceramics was examined by scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The polysiloxane-derived silicon carbide (PDSC) specimens showed a more homogeneous pore distribution than the powder-processed ones. Both the PDSC and powder-processed specimens contained only β -SiC when sintered at 1700°C. On the other hand, the PDSC specimens sintered at 2000°C revealed the formation of free Si clusters, detected by XRD and Raman spectroscopy, whereas the powderprocessed ones showed only the SiC phases. The formation of such Si clusters was effectively suppressed by adding an excess of carbon during the synthetic process. Raman spectroscopy revealed the existence of carbon layers in the 1700°C-sintered specimens, which were hardly detectable in the 2000°C-sintered ones.

Eu-doped yttria (Y 2¹x Eu x O 3 ) thin-film phosphors were prepared using a solgel process with post-annealing at 900°C. The Y 2¹x Eu x O 3 samples showed cubic bixbyite structure with a gradual increase in the lattice constant (¯0.5%) as x increases (¯0.22). The Eu-doped films exhibited strong photoluminescence (PL) near 2 eV at room temperature with well-resolved fluorescence peaks being ascribed to spin-flip f-f transitions,) ion. Among the six fluorescence lines, the intensity of the strongest 2.03-eV line (J = 2) varies significantly with the Eu content and its optimum value for the maximum PL strength is likely to be near x = 0.1. The Eu-doped films on the Al 2 O 3 substrates exhibited significantly higher PL intensities than those on the Si substrates despite no significant difference in structural properties between the two species being observed. It can be understood by comparing the change of complex refractive index for the Y 2¹x Eu x O