Preparation and thermoelectric transport properties of Ba-, La- and Ag- doped Ca3Co4O9 oxide materials

The Ba-, La- and Ag-doped polycrystalline Ca2.9M0.1Co4O9 (M=Ca, Ba, La, Ag) thermoelectric bulk samples were prepared via citrate acid sol-gel synthesis method followed by spark plasma sintering technique. The bulk samples were characterized and analyzed with regard to their phase compositions, grain orientations as well as microstructures. The high temperature thermoelectric transport properties of the bulk samples were studied in detail. All bulk samples were found to be single-phased with modified body texture. The electrical resistivity was modulated as a result of carrier concentration modification, however the carrier transport process was not influenced; the Seebeck coefficient was deteriorated simultaneously. The total thermal conductivity was remarkably reduced, on account of the decreasing of phonon thermal conductivity. The thermoelectric properties of the Ba-, La-, and Ag-doped bulk samples were optimized, and the Ba-doped Ca2.9Ba0.1Co4O9 system was found to have the highest dimensionless figure of merit ZT0.20 at 973K, which was remarkably higher than that of the un-doped sample.     

Effect of Y-filling on thermoelectric properties of CoSb3

The CoSb3 and Y0.18Co4Sb12 compounds were synthesized by a metallurgical route. Their bulk materials were prepared by the hot-pressed process under vacuum. Thermoelectric properties of the samples were measured by the thermoelectric measurement system and the laser flash diffusivity apparatus. The carrier type conversion of hot-pressed CoSb3 was found at about 530 K, while the conversion was missed for the Y0.18Co4Sb12 sample. Electrical conductivity of the Y0.18Co4Sb12 sample increased due to the increase of carrier concentration, and its thermal conductivity decreased due to the enhancement of phonon scattering. The value of ZT, figure of merit, for the Y0.18Co4Sb12 sample was obviously enhanced due to positive contribution of the electrical conductivity and the thermal conductivity.     

Effect of erbium substitution on thermoelectric properties of complex oxide Ca3Co2O6 at high temperatures

Polycrystalline particles of Ca3-xErxCo2O6 （x=0.0, 0.15, 0.3, 0.45 and 0.6） were synthesized using sol-gel method combined with Low Temperature Sintering procedure （LTS） to evaluate the effect of Er substitution on the thermoelectric properties of Ca3Co2O6. The crystal structure and microstructure were investigated using X-ray diffraction, infrared spectroscopy and scanning electron microscope. The electrical conductivity and Seebeck coefficient of the complex oxides were measured from 300 to 1073 K. The results showed that all the sampies were p-type semiconductors. The electrical conductivity increased with the increase in temperature. Er substitutions at Ca site affected carrier concentrations and carder mobility, resulting an increase in Seebeck coefficient and decrease in electrical conductivity. The power factor of Ca2.85Er0.15Co2O6 reached 10.66 μw/mK^2 at 1073 K.     

HPHT synthesis and electrical transport properties of SmxCo4Sb12

Samarium-filled skutterudites SmxCo4Sb12(x=0.5,1.0) skutterudite thermoelectric(TE) materials with enhanced power factor were prepared by high-pressure and high-temperature(HPHT) technique.The microstructure properties were characterized with X-ray diffraction and scanning electron microscopy.The electrical resistivities and Seebeck coefficients of those samples were measured in the temperature range of 300-723 K,and the samples of SmxCo4Sb12 showed n-type conduction.The Seebeck coefficient in absolute valu...     

Crystal Structures and Thermoelectric Properties of Sm-Filled Skutterudite Compounds Smy Fex Co4 - x Sb12

Polycrystalline samples of Sm partially filled skutterudites SmyFexCo4-xSb12 were prepared by melting and Spark Plasma Sintering technique. The results of Rietveld refinement showed that the obtained SmyFexCo4-xSb12 samples possessed filled skutterudite structures. The thermal parameter （B） of Sm is larger than that of Sb, Fe, and Co, indicating that Sm ＂rattled＂ in Sb-icosahedron voids. The effects of filling atom Sm on thermoelectric properties of these compounds were investigated. With the increase of Sm filling fraction （y）, electrical conductivity decreased, Seebeck coefficient increased and had a maximum value when y was 0.38; thermal conductivity reduced and had a minimum value when y was 0. 32. At 750 K, the highest figure of merit of 0.68 was obtained for Sm0.32Fe1.47Co2.53Sb12.     

Influences of Nd~（3＋） doping on structure and electrochemical performance of layered Li_（1.05）V_3O_8

Nd3+-doped Li1.05V3O8 was synthesized by liquid-state reactions combined calcination.The influences of Nd3+ doping on physical and electrochemical performances of Li1.05V3O8 were investigated using X-ray diffraction (XRD),cyclic voltammograms,a.c.impedance and galvanostatic charge-discharge tests,etc.Results indicated that Nd3+-doped products had well developed crystal structure of layered LiV3O8 and uniform particle size distribution.Nd3+ doping with a proper amount improved the initial discharge capacity,discharge voltage and ion conductivity of the cathode material to some extent.Nd3+ did not participate in the electrochemical reactions and was beneficial to stability of the crystal structure during cycling.     

Effect of different dopants on the long lasting phosphorescence behavior of CaTiO_3：Pr~（3＋）

In order to improve the luminescence properties of CaTiO3:Pr3+, a series of CaTiO3:Pr3+, such as CaTi0.97Nb0.03O3:Pr3+, Ca0.8Zn0.2TiO3: Pr3+, Ca0.8Zn0.2Ti0.97Nb0.03O3:Pr3+ and B3+-doped Ca0.8Zn0.2Ti0.97Nb0.03O3: Pr3+ were prepared through conventional solid state reaction method. The results of the photoluminescence excitation and emission spectra showed that all the samples emitted red phosphorescence at 612 nm originating from 1D2 to 3H4 emission of Pr3+ under the 337 nm excitation. When examined by the X-ray diffraction (XRD), all the samples presented a predominant phase of CaTiO3 (JCPDS# 42-423) except Zn2+-doped samples which also revealed another phase of Zn2Ti3O8 (JCPDS# 73-579). The results of the afterglow decay curves showed that co-doping Zn2+ ions, Nb5+ ions or adding a small amount of B3+ into Ca0.8Zn0.2Ti0.97Nb0.03O3:Pr3+ were effective in improving the photoluminescence properties of CaTiO3:Pr3+ phosphor. Thermoluminescence results showed that the trap existing in all the samples was the same as in CaTiO3:Pr3+ and doping singly Nb5+ or Zn2+ hardly changed the trap depth but co-doping Nb5+ and Zn2+ could modify the trapping level from 0.63 to 1.26 eV distinctively. In addition, adding a certain amount of B3+ into CTO-PZN could also deepen the trap depth.     

Luminescent properties of praseodymium doped Y_2O_3 and LaAlO_3 nanocrystallites and polymer composites

Luminescent properties of Y2O3 and LaAlO3 nanopowders doped with Pr3+ ions and PMMA-based composite materials doped with these powders were reported.The set of active nanopowders differing in praseodymium ions concentration was prepared using sol-gel method and carefully characterized with respect to emission properties in the visible spectral range.In particular,the excitation and emission spectra were measured together with fluorescence decay profiles and the differences between optical properties of thes...     

Effect of metal doping into Ce0.5Zr0.5O2 on catalytic activity of MnOx/Ce0.5-xZr0.5-xM0.2xOy/Al2O3 for benzene combustion

The research investigated the effect of doping two metals separately or together into Ce0.5Zr0.5O2 on the catalytic activity of MnOx/Ce0.5–xZr0.5–xM0.2xOy/Al2O3 (M=Y, Mn, Y and Mn) for catalytic combustion of benzene. The prepared catalysts were characterized by X-ray diffraction (XRD), surface area analysis, oxygen storage capacity (OSC), and H2-temperature programmed reduction (H2-TPR). Cata-lytic test was performed on a conventional fixed bed flow reactor. The characterization results revealed that Y and Mn ions entered into the ceria-zirconia mixed oxides framework, which improved the textural properties and greatly promoted the MnOx dispersion on the support surface. The complete conversion temperature of benzene on MnOx/Ce0.4Zr0.4Y0.1Mn0.1Oy /Al2O3 was 563 K, and the selectivity of carbon dioxides was 99%. This catalyst could be applied in a wide range of GHSV and wide concentration condition, showing great potential for application.     

Effects of grain boundary ternary alloy doping on corrosion resistance of(Ce,Pr,Nd)-Fe-B permanent magnets

To satisfy the application of different environments,grain boundary doping is commonly used in the preparation of sintered magnets to improve the coercivity and the corrosion resistance.In this paper,the alloys were prepared by mixing different ratios of the master alloy(Ce,Pr,Nd)-Fe-B and the sintering aid(Pr,Nd)-Al.The coercivity of sintered(Ce,Pr,Nd)-Fe-B magnet is substantially enhanced by doping 2 wt%of(Pr,Nd)-Al,while the maximum energy product decreases slightly.We systematically investigated the corrosion behavior and micro structure of the sintered magnets in order to determine the mechanism of the degradation.The sintered(Ce,Pr,Nd)-Fe-B magnets with 2 wt% of(Pr,Nd)-Al addition exhibit the decreasing corrosion rate compared with others,due to the distribution of intergranular phases.The electrode potential difference between the main phase and the RE-rich phase is reduced by the addition of Al,improving the potential and stability of RE-rich phase due to the higher electrode potential of Al than that of Nd,Pr or Ce.In addition,the element distribution of the magnets doped by(Pr,Nd)-Al indicates that the Al-rich shell formed at the marginal area of the Ce-rich phase improves its stability.Therefo re,intergranular adding te rnary(Pr,Nd)-Al alloy powders results in both high coe rcivity and good corrosion resistance synchronously.     

Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy

Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction(XRD),EPMA,scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS).The results showed that the dendrites sizes of α phase were decreased by the Nd addition.When the amount of addition Nd was 1.6 wt.%,the alloy with the smallest α phase was obtained.The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front.Furthermore,the compound Al 2 Nd generated by the reaction of Al and Nd,which distributed at the phase boundary and inside β phase,could also restrain the growth of α phase.Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy,however,excessive Al 2 Nd might also become crack source and decrease the elongation.     

Effects of different ligands on luminescence properties of LaF3：Nd nanoparticles

A series of neodymium-doped lanthanum fluoride nanoparticles(NPs) were synthesized with hydrothermal method,and the effects of several ligands on the luminescence properties of the NPs were investigated.The X-ray diffraction(XRD) results indicated that the crystal phases of the modified NPs coincided with the standard spectrum.The transmission electron microscopy(TEM) showed that the samples were of similar size,shape and dispersibility.The infrared spectra suggested that the content of -OH groups as quenchers on the NPs surfaces decreased after modification.Compared with NPs modified by branched paraffin ligands,NPs conjugating ring-contained modifiers had less quenching effect and possessed stronger fluorescence intensity and longer fluorescence lifetime.     

Effects of NH3 annealing on interface and electrical properties of Gd-doped HfO2/Si stack

Effects of NH3 rapid thermal annealing(RTA) on the interface and electrical properties of Gd-doped HfO2(GDH)/Si stack were investigated.The process of NH3 annealing could significantly affect the crystallization,stoichiometric properties of GDH film and the interface characteristic of GDH/Si system.NH3 annealing also led to the decrease of interface layer thickness.The leakage current density of Pt/GDH/p-Si MOS capacitor without RTA was 2×10-3 A/cm2.After NH3 annealing,the leakage current density was about one order of magnitude lower(3.9×10-4A/cm2).The effective permittivity extracted from the C-V curves was～14.1 and ～13.1 for samples without and with RTA,respectively.     

Effects of Host Doping on Spectral and Long-Lasting Properties of Sm^3＋ -Doped Y2O2S

Gd- or Lu-doped long afterglow red phosphor Y2O2S：Sm^3＋ was synthesized using the high temperature flux fusion method. The obtained phosphors were analyzed using X-ray diffraction to determine the crystal structure, and the phase analyses show that the product is in single phase. The luminescence spectra and decay curve were measured on a Hitachi F-4500 fluorescence spectrophotometer. The decay time was determined on an ST-900PM weak light photometer. The analyses show that host doping of Lu improves both luminescence and decay time of the materials. The concentration of doped Lu and Sm was varied in order to determine the optimal condition and to synthesize the product with the best properties. The mechanism of the long afterglow was also briefly discussed.     

Effects of Nd, Sm, Gd, Dy, Er Dopant on Electrical Properties of BaTiO3 Ceramics

BaTiO3 ceramics doped with various quantities of Nd2O3, Sm2O3, Gd2O3, Dy2O3 and Er2O3 were prepared respectively ( the adulterate concentrations were 0. 001,0. 002, 0. 003, 0.005, 0. 007 mol fraction) through a sol-gel method and their electrical properties were researched. It is found that each adulteration of Nd2O3, Sm2O3 Gd2O3,Dy2O3 and Er2O3 all can make the resistivity of BaTiO3 ceramics decline , especially Sm2O3 and Gd2O3. When the addition of Sm2O3 is 0. 001 mol, the resistivity is the smallest, declining from 4.0 × 1012 to 6.5 × 103 Ω different kind of rare earth exhibits different regularity. The grain resistance of BaTiO3 ceramics doped with Sm2O3 or Gd2O3 exhibits a NTC effect, at the same time the grain boundary resistance has a PTC effect, and the grain boundary resistance is much larger than the grain resistance, so the PTC effects of BaTiO3 ceramics doped with Sm2O3 or Gd2O3 originate from the grain boundary. The additions of Nd2O3 , Gd2O3 or Er2O3 make the dielectric constant and the dielectric loss of BaTiO3 ceramics change evidently, especially Nd2O3. The dielectric constant is larger than that of pure BaTiO3 ceramics, on the other hand, the dielectric loss is much lower, which is useful in capacitor fields.     

Thermoelectric properties of LaFe_3CoSb_(12) skutterudite materials with different nanostructures

Nanostructures with different morphologies could profoundly influence the electron and phonon transport in thermoelectric materials and thus their properties could be improved by tuning the nanostructures.The LaFe3CoSb12 skutterudite nano powders with differentmorphologies were fabricated via a hydro/solvo thermal route.The microstructures of the hot-pressed LaFe3CoSb12 bulks were characterizedthrough X-ray diffraction(XRD) and scanning electron microscopy(SEM) and the effects of the nanostructures on the thermoelectric properties were investigated by measuring the electrical conductivity,the Seebeck coefficient and the thermal conductivity.The results suggestedthat the mixed morphology of nanorods and nanospheres could enhance the electrical conductivity largely although the Seebeck coefficientwas decreased and the thermal conductivity was increased slightly.Differently,a higher Seebeck coefficient,a lower thermal conductivity anda lower electrical conductivity could be obtained for the LaFe3CoSb12 bulk with a single morphology of nanospheres.Consequently,the figure of merit of LaFe3CoSb12 bulk with a mixed morphology of nanorods and nanospheres could be increased by about 59% as compared tothat with a single morphology of nanospheres.     

Synthesis and luminescence properties of BaWO4：Pr^3＋ microcrystal

BaWO4:Pr3+ (hereafter BWO:Pr) microcrystals were prepared via a hydrothermal route, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation and emission spectra. The as-prepared products with different morphologies of egg-shape rod, olive-like, and quasi-sphere were obtained by the addition of the surfactants and chelating agents. The emis-sion spectra of BWO:Pr microcrystals showed the strong red emission (642 nm) assigned to the Pr3+ ions of 3P0→3F2 transition with blue ex-citation (484.6 nm, 3H4→3P0).     

Influence of lanthanum doping on performance of LiFePO4 cathode materials for lithium-ion batteries

Using solid-state synthesis method,a series of samples of lanthanum doped Li1-xLaxFePO4(x=0.0025,0.005,0.0075,0.01) were prepared.Each cathode structural and electrochemical properties were investigated using X-ray diffractometry(XRD),scanning electron microscopy(SEM),electrochemical impedance spectroscopy(EIS) and charge/discharge cycling.Nanopowders material with single-phase could be obtained.The reversible capacity could be drastically improved by the introduction of La.The optimum cells with Li0.99La0....     

Effects of cerium doping position on physicochemical properties and catalytic performance in methanol total oxidation

The physicochemical properties of Pd and PdPt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N₂ adsorption-desorption, XPS and FT-IR. The catalytic performance for methanol total oxidation was examined to study the effects of Ce adding position. CeO₂Al₂O₃TiO₂ (CAT) catalysts that Ce is directly introduced into support show higher reactivity and CO₂ selectivity than CeO₂/Al₂O₃TiO₂ (Ce/AT) samples in which Ce is loaded by impregnation method. The characterization results reveal that the Ce doping position does not cause obvious otherness of basic crystalline phase and mesoporous structure of support. However, the Ce doping position affects the pore shapes of support and then influences the pore diameter. CAT catalysts possess more abundant adsorbed oxygen and more Ti³⁺ can transform the more gaseous oxygen into the active oxygen species on the catalyst surface, which is beneficial to the reaction. The AlOTi bridges in CAT facilitate the cooperation of Al and Ti species, which further speeds up the reaction rate.     

Microstructure and mechanical properties of Mg-7Zn-3Al alloy with Nd and Y additions

The effects of combined addition of 0.6 wt.% Nd and 0.4 wt.% Y on the microstructure and mechanical properties of Mg-7Zn-3Al alloy were investigated.The results indicated that the Nd and Y addition led to obvious dendrite coarsening.However,it could modify the morphology and distribution of-Mg 32(Al,Zn) 49 intermetallics.Moreover,Al 2 REZn 2 phase could be introduced into the alloy with the Nd and Y addition.With the effective second-phase strengthening,the ultimate tensile strength and elongation in as-cast state can be improved by the Nd and Y addition.After ageing treatment,the alloy with the Nd and Y addition exhibited better precipitation strengthening effects by forming finer MgZn 2 and Mg 32(Al,Zn) 49 precipitates into the-Mg matrix.As a result,the yield and ultimate strength of Mg-7Zn3Al-0.6Nd-0.4Y alloy could be increased to 182 and 300 MPa by peak-ageing treatment.