Key Engineering Materials Vol. 519

Abstract: The electronic structures of the titanium-doped cubic perovskite ruthenates BaRu_1-xTi_xO₃ with x=0.125, 0.25, 0.375, 0.5, 0.625, 0.75, and 0.875 are investigated using the spin-polarized density functional theory within the pseudopotential plane wave method. It is found that a half-metallic phase appears in the 0.75- and 0.875-doped systems, and the origin of half-metallic property is the decrease of t_2g bandwidth of Ru 4d states with the increase in x. In addition, the energy gap of BaRu_0.25Ti_0.75O₃ is as large as 1.7 eV at the Fermi level in the up-spin density of states, which suggests a stable half-metallic phase can be obtained in the present systems.

Abstract: The thermoelectric properties of Ag-doped and Ag/Sb codoped PbSe, prepared by furnace melting, quenching, ball milling and spark plasma sintering (SPS) techniques, were investigated. The X-ray diffraction (XRD) analysis indicated that all samples crystallize in the NaCl-type structure without noticeable secondary phase. The substitution of Ag¹⁺ ion for Pb²⁺ ion in PbSe caused the compound changed from n-type semiconductor to p-type semiconductor. The lower Ag doped sample Pb_1-xAg_xSe with x = 0.002 remains n-type conduction of PbSe, shows high electrical resistivity and thus low figure of merit (ZT). However, the higher Ag doped samples Pb_1-xAg_xSe with x = 0.004, 0.006, 0.008 exhibit n-type conduction, low electrical resistivity and thus leads to the higher ZT. The maximum ZT of the alloy Pb_0.996Ag_0.004Se reaches 0.66 at 673K, much higher than 0.24 of PbSe at the same temperature. A proper Sb doping in the n-type semiconductor Pb_0.998Ag_0.002Se can remain its n-type semiconductor, modify the carrier concentration, decrease the electrical resistivity and thus enhance the thermoelectric property. The alloy Sb0.002Pb0.998Ag0.002Se shows a ZT value of 0.59 at 573K, much higher than 0.26 of the sample Pb_0.998Ag_0.002Se at the same temperature.

Abstract: LaNiO₃ single layer, LaNiO₃/LaAlO₃ superlattice on vicinal-cut single crystalline LaAlO₃ (100) and LSAT (100) substrates were prepared by pulsed laser deposition technique. Single-phased LaNiO₃ polycrystal target, which is synthesized by sol-gel method, is employed in the thin film deposition process. The structure and physical properties of both the targets and thin films are analyzed. X-ray diffraction results show LaNiO₃ single layer is of c-orientation and textural growth, therefore LaNiO₃/LaAlO₃ forms not superlattice but multilayer. The ultra-violet LITV (laser induced thermoelectric voltage) effects of the LaNiO₃/LaAlO₃ mutilayer and LaNiO₃ single layer were investigated. A comparison study of the influence of LaNiO₃ targets prepared by different sol-gel method on the physical property, and LITV effect of thin films was performed as well.

Abstract: Here we report the thermoelectric properties of a wide–gap chalcopyrite compound AgInSe₂, and observed the remarkable improvement in electrical conductivity σ, due to the bandgap (E_g = 1.12 eV) reduction compared to In₂Se₃. The improvement in σ is directly responsible for the enhancement of thermoelectric figure of merit ZT, though the thermal conductivity is much higher at 500 ~ 724 K. The maximum ZT value is 0.34 at 724 K, increasing by a factor of 4, indicating that this chalcopyrite compound is of a potential thermoelectric candidate if further optimizations of chemical compositions and structure are made.

Abstract: The deposition rate(r) of pyrocarbon deposited from propylene pyrolysis has been explored as a function of residence time (tr=0.2-5s) and deposition temperature (T=1173-1333K) at a constant pressure of 6 kPa. The main feature of r vs. curves was that the deposition rate, firstly increase and then decrease with the residence time. A qualitative chemical model was developed and the kinetic domains were defined for the formation of pyrocarbon. The model could explain the change of deposition rates and kinetic transition due to the occurrence of two different families of ultimate carbon precursor.

Abstract: Manganese oxide (MnO2)/Carbon nanotubes(CNTs) composites were prepared by a home-made microwave heating equipment. The crystal structure, microstructure, electrochemical properties were characterized by XRD and SEM, the discharge capacity and cycling performance were compared. The results show a birnessite-type MnO2 coating can be prepared. In this paper, a microwave-assisted hydrothermal synthesis method was used to synthesize the MnO2/CNTs composites. MnO2 content increases with the increasing of microwave power, which result in the specific capacitances of as-perpared materials increase

Abstract: In this paper, a combination of in-situ polymerization and ultrasonication dispersion method has been successfully utilized to prepare r-GO/carbon sphere/PANI trinary composite. The structural characterizations show that the carbon sphere/PANI composites are wrapped by r-GO sheets in the as-obtained composites. Due to the reinforcing effect coming from r-GO, the efficient charge and ions transport, conductivity, and electrochemical performance of carbon sphere/PANI composite are significantly improved after combining with the r-GO. The r-GO/carbon sphere/PANI composite exhibits the largest specific capacitance of 420 F g-1, about 75% higher than that of carbon sphere/PANI binary composite (240 F g-1). Therefore, such r-GO/carbon sphere/PANI composite can be a potential candidate for high-performance capacitors.

Abstract: Graphene-like carbon materials (GCMs) are prepared by the carbonization of liquid acrylonitrile oligomer (LANO) at 600-1400 °C for 4 h in an Ar atmosphere. LANO undergoes thermal oxidative dehydrogenation and preliminary cyclization by pre-process in air at low temperature (120 °C) and high temperature (220 °C) before the carbonization. Surface chemistry，crystalline and pore structures of the GCMs are characterized by scanning electron microscope (SEM), power X-ray diffraction (XRD) and N2 adsorption respectively. Comparison of the effect of various carbonization temperatures on the electrochemical performance of the electric double layer capacitors (EDLCs) is specifically investigated. The GCMs carbonized at 1300 °C for 4 h shows a fairly good electrochemical performance. The BET surface area of GCM1300 is 81.58 m2/g and the specific capacitance of the GCM1300 is 22.52 F/g in 1 mol/ L Et4NBF4/PC electrolytes.

Abstract: Removed at authors request.

Abstract: Abstract: Manganese zinc ferrite/barium ferrite composite materials were prepared with various content of Z type barium ferrite (0, 10, 20 wt%) using solid state reaction method. The effect of the compositon on the microstructure and electromagnetic properties of the composites are investigated by means of X-ray diffraction, scanning electron microscope and impedance analyzer. The X-ray diffraction patterns reveal that W phase of barium ferrite instead of Z phase appears in the composite sintered as well as the spinel phase. Some small hexagonal grains were observed in the SEM images and the proportion increases with increasing content of barium ferrite. The cut-off frequencies of the composite systematically shift towards high frequency from 2.5 MHz to 32.6 MHz which is attributed to the increasing of W phase. The composites show a higher frequency for the maximum of the impedance as well as a higher value of the impedance at certain frequency which may be benefit for the application at GHz frequency range.