Erosion wear behavior of MgO stabilized ZrO₂ (MgSZ) ceramics was studied at elevated temperature by a self-made solid particle impact erosion wear testing apparatus. Volume erosion wear rate of MgSZ ceramics was measured at up to 1400°C with an impact angle of 90°. The effects of erosion temperature on erosion wear behavior and mechanism for different temperature ranges have been discussed. The results indicate that volume erosion wear rate of MgSZ ceramics increased with temperature. Specifically, volume erosion wear rate increased at a rate of 1.87 × 10⁻⁴ from room temperature to 600°C, 5.99 × 10⁻⁴ from 800 to 1000°C, and tended to be constant from 1000 to 1400°C. Volume erosion wear rate reached its maximum value of 0.60 mm³/g at around 1000°C. The increase in erosion wear rate is related to the decrease in mechanical performance of MgSZ with increasing temperature. When MgSZ ceramics were impacted by corundum particles, the main material removal mechanism was found to be plastic deformation from room temperature to 600°C and crack crisscross leading to flaky exfoliation of material from 1000 to 1400°C. Between 600 and 800°C, a transition region from plastic deformation to flaky exfoliation was found.

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Frequency selective surface (FSS) based on ceramic materials is very promising due to its high temperature bearing capacity along with stealth properties for high-speed aircraft. In this paper, modified silica ceramic, which is compatible for High Temperature Co-fired Ceramic (HTCC) technology, was investigated. The flexural strength of the Li₂O–K₂O–Al₂O₃ doped silica ceramic reaches 163.65 MPa at a sintering temperature of 1325°C, which greatly surpasses that of conventional fused silica. The maximum density of the ceramic is 2.113 g/cm³. The dielectric constant is 4.37 and the dissipation factor is 0.0038 at 14 GHz. Based on the modified silica ceramic, a Jerusalem element FSS was designed and optimized. Results show that the Jerusalem element FSS owes its advantages to high transmission coefficient, appropriate bandwidth, flat pass band and stability with different polarizations.

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Magnesium phosphate glasses exhibit unusual properties and were classified as ‘anomalous phosphate glasses’, because magnesium is attributed to a variation of the oxygen coordination number from 6 to 4. Magnesium in phosphate glasses acts as an intermediate oxide and its role was determined, relating to the phosphate chain length. In the present work, MgO–P₂O₅–TiO₂/Nb₂O₅ glasses with Mg/P ratio between 1.00 and 1.36 were successfully prepared by a melt–quenching method. Magnesium in the glasses worked as a network former to form P–O–Mg bonds, which are cross-linked short phosphate chains that improved the glass-forming ability. Intermediate oxides (i.e., TiO₂ and Nb₂O₅) in the glasses also cross-linked short phosphate chains to form P–O–Ti/Nb bonds. The chemical durability of the glasses decreased with an increase in the Mg/P ratio, because magnesium, which entered the phosphate network, weakened the glass network to induce hydrolysis. The dissolution rate of Ti⁴⁺ and Nb⁵⁺ ions showed a decreasing tendency with an increase in the Mg/P ratio. The surfaces of the glasses were considered to be covered with gel-like oxide layers containing titanium or niobium and phosphate.

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Glass-ceramics based on nepheline crystal (Na₃(Na,K)[Al₄Si₄O₁₆]) system was modified to satisfy the thermal and optical properties required for a band-pass filter (BPF) in telecommunication systems using optical fibers. The suitable coefficient of thermal expansion was achieved in a glass-ceramic containing more potassium oxide than the conventional nepheline glass-ceramics, in nepheline–kalsilite (K[AlSiO₄]) binary system. An addition of the moderate amount of nucleating agents is a key parameter to obtain high transparency of the glass-ceramics. The optimized nepheline–kalsilite glass-ceramic showed higher mechanical strength as compared with the monolithic glassy material used in the same application.

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The synergistic effects of CeO₂-supported bimetallic Ni–Cu, Co–Cu, and Ni–Fe catalysts on the reduction properties, crystal structure, and catalytic performance during steam reforming of ethanol were investigated. Both metals in the bimetallic catalysts were reduced at lower temperatures than were the metals in the associated monometallic catalysts, and they formed alloy crystallites. It was confirmed from activity tests of the monometallic catalysts that Ni and Co were relatively active components and that Cu and Fe were less active. The combination of Ni and Co with Cu (Ni–Cu/CeO₂ and Co–Cu/CeO₂) resulted in increases in H₂ and CO₂ yields and inhibition of carbon deposition during reactions at 673 K. On the other hand, the incorporation of Ni with Fe (Ni–Fe/CeO₂) showed a lower activity than did Ni/CeO₂ at 673 K but exhibited a higher H₂ yield and higher resistance to carbon deposition at 873 K, in which case NiFe alloys were formed. These results indicate the advantages of alloying a catalytically active metal with a less active metal during steam reforming of ethanol.

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Sm₂O₃/SmFeO₃ mixed powders were applied to a chemo-resistive VOC (volatile organic compound) gas sensor. The sensor response to 30 ppm toluene gas increased with increasing the Sm₂O₃ content up to 30 wt %, but decreased by further adding. The addition of Sm₂O₃ up to 30 wt % also enhanced the catalytic activity for toluene oxidation, as the result of the sensor response. The amount of toluene adsorption increased with increase in the surface Sm concentration. It was concluded that adding Sm₂O₃ increased the amount of adsorbed VOCs, resulting in the enhancement of the sensor response and the catalytic activity. Furthermore, adding Sm₂O₃ remarkably shortened the recovery time from the VOCs to air. For the ethanol sensing, adding Sm₂O₃ was only effective on shortening the recovery time.

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Double-layer electrodes using TiO₂-P25 as the first layer and SrTiO₃ or BaTiO₃ as the second layer were prepared to improve photovoltaic performance of dye-sensitized solar cells (DSCs), since SrTiO₃ and BaTiO₃ have more negative conduction bands than that of TiO₂. TiO₂-anatase second layer with the similar particle size to these double oxides was also prepared as a comparison. Crystal structure, microstructure, film thickness, amount of dye adsorption, J–V curves and IPCE spectra were characterized. Open-circuit voltage (V_OC) of the DSCs with the SrTiO₃ or BaTiO₃ second layer was improved due to the inhibition of electron–hole recombination by the second layer at the top side of the TiO₂ first layer. Elongation of the electron life time due to the band-structure matching might be another reason of the increase in V_OC. By using the second layer, short-circuit current density (J_SC) was also slightly improved (∼4%), possibly due to the increase of electrode thickness and light confinement effect for >∼650 nm. As a result, the DSC using BaTiO₃ second layer electrode had the largest conversion efficiency of 5.71% with an enhancement of 11.3% compared to that of TiO₂-P25 single-layer electrode.

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0.7BiFeO₃–0.3BaTiO₃ + 1 mol % MnO₂ + x mol % Co₂O₃ multiferroic ceramics were fabricated by an ordinary sintering technique and the effects of Co doping on the microstructure, multiferroic and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure with rhombohedral symmetry. The addition of a small amount of Co₂O₃ enhances the ferroelectricity, ferromagnetism, piezoelectricity and temperature stability of the ceramics. The ceramic with x = 1.0 possesses enhanced piezoelectricity (d₃₃ = 134 pC/N), good ferroelectricity (P_r = 19.9 µC/cm²) and increased high depolarization temperature (T_d = 475°C). The 1 mol % Co₂O₃ doping greatly improves the ferromagnetic property of the ceramics and the optimum remnant magnetization M_r of 0.191 emu/g of the ceramic is obtained at x = 1.0. These results show that the ceramic with x = 1.0 is a promising candidate for lead-free high-temperature piezoelectric and room-temperature multiferrioc materials.

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We present the results of experiments that assess the viability of the polymerizable complex method to synthesize sodium bismuth titanate Na_0.5Bi_0.5TiO₃ (NBT) while preventing sodium and bismuth from evaporating. To synthesize NBT with the stoichiometric composition and no sodium and bismuth deficiencies, it is of vital importance to direct our attention to preventing the evaporation of sodium and bismuth, which can easily occur in high-temperature sintering. X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG–DTA) of precursors synthesized by the polymerizable complex method revealed a crystallization temperature located at a temperature between 300 and 400°C. The ¹³C NMR results show the peak intensity derived from residual organics decreased with an increase in the calcining temperature. The complete single phase in NBT was obtained at a temperature higher than 600°C. From ferroelectric hysteresis loops, values of the remanent polarization were larger for the samples synthesized by the polymerizable complex method than for those by the solid-state reaction method. This result indicates that the NBT samples synthesized by the polymerizable complex method retain their stoichiometric compositions even if they are calcined at high temperatures below the melting point of NBT, which is supported by the results of Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES).

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Carbon contamination caused during spark-plasma-sintering (SPS) processing was investigated in the MgAl₂O₄ spinel by Raman spectroscopy. Although the carbon contamination became remarkable around the sample surfaces directly contacting the carbon paper, it sensitively changes with the SPS conditions, particularly for the heating rate. For the slow heating rate of 10°C/min, the carbon contamination can be detected around the surface regions rather than inside. For the high heating rate, however, a large amount of the carbon contamination was detected even inside in addition to the significant contamination around the surfaces even though the sintering temperature is the same and the processing time is shorter as compared to those of the slow heating rate. The present results suggest that the carbon contamination is not caused by diffusion processes, but caused by evaporation of the carbon phase from the carbon paper/dies, which were used in the SPS process. For the high heating rates, the carbon evaporation is enhanced due to the rapid heating and goes into the samples through open pore channels. The evaporated carbon is encapsulated into the closed pores during the heating process and remains along the grain junctions as glassy carbon.

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Li⁺-doped cubic Gd_1.88Eu_0.12O₃ phosphors were synthesized at 1200°C in air by co-precipitation (CP) and solid state reaction (SS) methods. X-ray diffraction analysis revealed that, regardless of synthetic method, the average crystallite size for Li⁺-free Gd_1.88Eu_0.12O₃ was approximately 400 nm, then increased with the amount of Li⁺ and at 20 mol %, reached about 2.3 µm. Under excitation of the charge transfer band of Eu³⁺ at 245 nm, Gd_1.88Eu_0.12O₃ exhibited a dominant photoluminescence (PL) red emission peak at 611 nm assigned to the electric dipole transition ⁵D₀→⁷F₂ of Eu³⁺. The red emission peak intensity increased consistently with the amount of Li⁺-doping, while CP method was found to be effective in improving the red emission intensity at lower amounts of Li⁺-doping from 0 to 8 mol %. Cathodoluminescence (CL) property was studied by mounting the synthesized phosphor on a vacuum fluorescent display (VFD) operated at an anode voltage of 50 V. The Gd_1.88Eu_0.12O₃ exhibited a similar spectrum with an intense red emission peak at 611 nm, and the highest luminance intensity for the CL red emission was achieved for 8 mol % Li⁺-doped Gd_1.88Eu_0.12O₃ synthesized by SS method. The evaluation results of PL and CL properties suggested that, besides the crystallite size of Gd_1.88Eu_0.12O₃, dispersion property of Eu³⁺ ions in the host Gd₂O₃ was an important factor for improving luminescent properties of Gd_1.88Eu_0.12O₃. Moreover, under the present VFD operating condition at the low excitation voltage, it was thought to be essential for improving CL emission intensity to maintain a sufficient surface area of Gd_1.88Eu_0.12O₃.

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The effect of Zr addition into malic acid complex was examined for the purpose of the improvement of microstructure and specific surface area of CaFe₂O₄. The CaFe₂O₄ phase could be obtained for both unadded and Zr-added (5 and 10 mol % with respect to Fe) system by calcination of precursor derived from malic acid complex at 700°C which is almost 200°C lower than that of conventional solid-state reaction method. Among the examined products, only the 5 mol % Zr-added product revealed characteristic smaller grains connected three dimensional porous structures resulting in higher specific surface area compared with unadded and 10 mol % Zr-added products. XPS measurements revealed that there are no notable changes in valence state for all constituent elements. The obtained final product of 5 mol % Zr-added CaFe₂O₄ is worth further investigate for various application from a view point of improved higher specific surface area and characteristic microstructure as well as the functionality of the material itself.

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