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[en] The transport property () and flux motion together with the superconductivity of Fe Se2 single crystals are studied. In the transport measurement, contrasting behavior is observed under two different magnetic field orientations, i.e., and , which is ascribed to different vortex configurations. In the flux motion study, the tail of the well fits the description of the vortex-glass (VG) critical behavior, which is confirmed by VG scaling. The strong pinning nature of FeSe2 implies great sustainability under high magnetic fields and the potential for practical application of the system. The relation under T c follows Arrhenius thermally activated flux flow (TAFF) behavior. The existence of a crossover behavior in a magnetic field is discovered via the magnetic dependence of the effective pinning barrier, which is related to the change in pinning strength of the point defects and the entanglements of the flux lines. Finally, a vortex phase diagram is proposed based on the evolution of upper critical field and other dynamic characteristics. (paper)
[en] Research highlights: → The YBA glass has been studied as potential SOFC sealants. The resistivity of the YBA glass below 800 oC is over 9.1 x 104 Ω cm which can fulfill the requirement of SOFC. The YBA glass has a CTE of 11.64 x 10-6 K-1 near other SOFC components below 873 K and it becomes flexible over that temperature. It was proved the YBA glass adhere well to YSZ and other SOFC components according to the SEM photos. Preliminary results demonstrated that the YBA glass was the most promising sealant for planar SOFC. - Abstract: A glass based on Y2O3-BaO-SiO2-B2O3-Al2O3 (named YBA) has been investigated as sealant for planar solid oxide fuel cells (SOFCs). The YBA glass has been systematically characterized by differential thermal analysis, dilatometer, scanning electron microscopy, impedance analysis, and open circuit voltage to examine their suitability as sealant. The coefficient of thermal expansion of YBA is 11.64 x 10-6 K-1 between 323 and 873 K. The resistivity is 9.1 x 104 Ω cm at 800 oC. The glass sealant is found to be well adhered with other cell components, such as electrolytes and stainless steels, at an optimum sealing temperature of 800 oC. All measured results showed that the YBA glass appears to be a promising sealant for SOFCs.
[en] The transport and thermoelectric properties together with annealing of the new layered Bi-chalcogenide LaOBiHgS3 are studied. On the transport part, the insulating behavior of the as-grown sample is evidently depressed by post annealing. A hump-like abnormality appears around 170 K. The thermoelectric performance of the sample is observably improved by the annealing, mainly because of the enhanced electrical conductance. The present results suggest that the physical properties of LaOBiHgS3 are sensitive to post annealing and the possible micro adjustments that follow, indicating the layered Bi-chalcogenide family to be an ideal platform for designing novel functional materials. (paper)
[en] MnTiO3 ceramics were prepared via the traditional solid-state reaction route. The low-temperature (100-330 K) dielectric properties of MnTiO3 have been systematically investigated in the frequency range from 100 Hz to 5 MHz. Our results showed that MnTiO3 exhibits intrinsic dilectric response in a wide temperature range up to 200 K. A relaxation appears near room temperature. This relaxation can be enhanced by annealing treatment in oxygen and weakened in nitrogen. Reducing the sample thickness gradually leads to the disappearance of the relaxation. Based on these experimental facts, the relaxation was ascribed to be a Maxwell-Wagner relaxation due to surface-layer effect.
[en] Gd0.5Na0.5TiO3 ceramic samples were prepared by the solid-state reaction method. Incipient ferroelectricity was confirmed in the sample. Dielectric properties were investigated at temperatures from room temperature to 1073 K and the frequency range of 20 Hz–10 MHz. By means of electric modulus and impedance analysis, the sample was found to show two thermally activated relaxations with the high-frequency (low-temperature) one being the relaxation caused by hopping motion of oxygen vacancies and the low-frequency (high-temperature) one being the interfacial relaxation
[en] Double-perovskite Ba2YMoO6 ceramics were prepared via the solid-state reaction route. Their dielectric properties were investigated as a function of temperature (100 °C≤T≤800 °C) and frequency (300 Hz≤f≤5 MHz). In the temperature below 600 °C, two thermally activated dielectric relaxations can be well identified. The low-temperature relaxation was ascribed to be a dipolar relaxation caused by oxygen vacancy diffusion, and the high-temperature relaxation is found to be a Maxwell–Wagner relaxation due to surface-layer effect
[en] The electrical and dielectric properties of MgF2 single crystals were investigated in the temperature range of 11–800 °C and the frequency range of 20 Hz–10 MHz using impedance and modulus spectroscopy. Impedance analysis revealed that MgF2 shows intrinsic dielectric properties below ∼500 °C. A thermally activated relaxation at higher temperatures was observed, which was ascribed to be a Debye-type relaxation caused by the mobility of fluorine interstitials. The result indicates that MgF2 holds great promising applications as gate dielectric, substrate materials, and buffer layer in silicon technology.
[en] Upon annealing polycrystalline La0.67Ba0.33MnO3 bulk samples in flowing 95%Ar:5%H2 mixed gas at 700oC for different time, the insulator-metal transition temperature, TP and the amplitude of AC magnetic susceptibility were decreased first, then increased, finally decreased again. While the resistivity was increased monotonically. This anomalous behavior was explained by the combinational effects of oxygen loss and Ba ion vacancies caused by the segregation of Ba ion related impurity phase
[en] Polycrystalline perovskite La0.8Tb0.2MnO3 (LTMO) with an orthorhombic phase was synthesized by conventional solid-state reaction. The magnetic and electric properties of La0.8Tb0.2MnO3 were examined. The striking finding is that the material exhibits giant magnetoresistance at room temperature as high as -31.8% and -35.7% under the low magnetic fields of 100 and 1000 Oe, respectively. This result suggests that La0.8Tb0.2MnO3 has a promising potential in future device developments
[en] Highlights: • The SrSc0.175Nb0.025Co0.8O3-δ perovskite was evaluated for proton conducting SOFC. • Polarization resistance of SSNC decreased obviously via introducing H2O in gas phase. • The symmetrical cell showed the lowest Rp of 0.26 Ω cm−2 at 600 °C in 3% H2O-air. • This study suggests that in situ creation of H+ is possible at the SSNC cathode. - Abstract: Proton-conducting solid oxide fuel cells (H+-SOFCs) have attracted considerable interest recently. However, the overall cell performance of H+-SOFCs is still low due to the lack of a promising cathode material. In this study, SrSc0.175Nb0.025Co0.8O3-δ (SSNC) was synthesized for evaluation as a cathode material in H+-SOFCs based on a BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte. The chemical compatibility and stability of the SSNC cathode with the BZCY electrolyte in humidified air were studied. In addition, the electrochemical behavior of the SSNC cathode on the BZCY electrolyte was investigated using SSNC/BZCY/SSNC symmetrical cells at 600 °C in dry air and humidified air at various H2O partial pressures. Promising electrocatalytic activity was observed for the SSNC cathode in humidified air. The area specific resistance obtained on symmetrical cells at 600 °C in a 10% H2O-air atmosphere was 0.26 Ω cm2. A promising peak power density of 498 mW cm−2 was obtained using an anode-supported cell with a 46 μm-thick BZCY electrolyte layer at 700 °C.