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1.
Polycrystalline Ca3Co1.8M0.2O6 (M=Mn, Fe, Co, Ni, Cu) and Ca2.7Na0.3Co2O6 were synthesized by solid-state reaction to evaluate the effect of substitution on the thermoelectric properties of Ca3Co2O6. Substitution by Mn, Cu and Na appears to increase carrier density, given that electrical resistivity (ρ) and the Seebeck coefficient (S) were simultaneously reduced. Conversely, Fe substitution seems to reduce carrier density, resulting in a simultaneous increase in S and ρ. Cu and Na substitution resulted in a significant decrease in ρ due to enhancement of grain size and grain boundary connectivity, which could have a strong impact on ρ. Not only the intrinsic substitution effect on the electronic state but also this modification of the microstructure plays an important role in improvement of the thermoelectric power factor, particularly in the case of the Na-substituted sample.  相似文献   

2.
The precursors of Co3O4 and Ag/Co3O4 composites with different Ag contents were synthesized with assistance of (NH4)2CO3 via a facile hydrothermal process. The final samples were fabricated by calcining each precursor at 400 °C according to TG experiment. The as-prepared samples were identified and characterized by thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy, respectively. The results showed that the morphology of Co3O4 and Ag/Co3O4 composites were sheet-like. Ag nanoparticles were dispersed well in the nanosheets. The samples were used as electrocatalysts modified directly on a glassy carbon electrode for p-nitrophenol reduction in a basic solution. The results showed that p-nitrophenol could be reduced at a large peak current but a higher peak potential with Co3O4, at lower potentials with Ag/Co3O4 composites. Ag/Co3O4 composite with 3 % Ag showed more efficiently electrocatalytic activity than other composites. The present method suggested the potential application of Ag/Co3O4 composites in electrocatalysis.  相似文献   

3.
Thermoelectric NaxCo2O4/Ag composites were synthesized by citric acid complex (CAC) method and Ag precipitation from CH3COOAg aqueous solution on the NaxCo2O4 powders. Effects of the synthesis process on microstructure and thermoelectric performance of NaxCo2O4/Ag composites were investigated. When the NaxCo2O4 CAC powders were dipped in CH3COOAg aqueous solution and dried, fine Ag particles less than around 300 nm in size were precipitated on the surface of NaxCo2O4 powders. After the subsequent sintering process, the flaky Ag phase, the length and thickness of which were up to 5 and 1 μm, respectively, existed along interfaces between NaxCo2O4 grains. The sizes of Ag particles obtained in this study were found to be smaller than those of the conventionally prepared NaxCo2O4/Ag composites. The fine dispersion of Ag grains was effective for suppressing the increase in thermal conductivity due to the addition of metallic phase, Ag, and for improving the thermoelectric performance of NaxCo2O4/Ag composites, suggesting that the synthesis technique composed of the CAC method and Ag precipitation from CH3COOAg aqueous solution is significantly important process for thermoelectric NaxCo2O4/Ag composites.  相似文献   

4.
Sheet-like precursors of Co3O4 and Ag/Co3O4 composites with different Ag contents were synthesized with assistance of triethylamine via a hydrothermal process. The final samples were fabricated by calcing each precursor at 400 °C. The as-prepared samples were identified and characterized by thermogravimetric analysis and differential thermal analysis, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy, respectively. The Co3O4 and Ag/Co3O4 composite samples were used as electrocatalysts modified on a glassy carbon electrode for p-nitrophenol reduction in a basic solution. The electrocatalytic results indicated that all the samples showed enhanced electrocatalytic performance for p-nitrophenol by comparing a bare glass carbon electrode, and p-nitrophenol could be reduced by Co3O4 at a high peak current but a rather higher peak potential but be reduced effectively by Ag/Co3O4 composites at lower potential. Ag/Co3O4 composites with 4 % Ag displayed the highest electrocatalytic activity.  相似文献   

5.
Sr3In0.9Co1.1O6, isostructural to Ca3Co2O6, is revealed by the study of the phase relations in the system SrO-InO1.5-CoOx (1000 °C). The structure of Sr3In0.9Co1.1O6 is refined by the combination of powder X-ray and neutron diffraction. Sr3In0.9Co1.1O6 crystallizes in a trigonal lattice with the cell parameters a=b=9.59438(3) Å, c=11.02172(4) Å with the space group R-3c. Its structure possesses 1D (In/Co)O3 chains running along the c-axis constructed by alternating face-sharing CoO6 octahedra and (In0.9Co0.1)O6 trigonal prisms. The co-occupation of In3+ and Co3+ at the trigonal prismatic site is evidenced by elementary analysis and determined by the structure refinement. Sr3In0.9Co1.1O6 is paramagnetic, and the susceptibility is consistent with the occupation of Co3+ at 10% of the trigonal prismatic positions in a high spin state (HS, S=2). The HS Co3+ is well separated by diamagnetic CoO6 octahedra and InO6 trigonal prisms and shows a g factor of 2.0 in the magnetic measurements.  相似文献   

6.
以六水合硝酸钴[Co(NO_3)_2·6H_2O]为钴源、六水合硝酸锌[Zn(NO_3)_2·6H_2O]为锌源、2,2′-硫代二乙酸(C4H6O4S)为硫源,采用溶剂热法制备出了片状的Co_9S_8/ZnS/C复合材料。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和N_2吸附/脱附测试等手段对于片状Co_9S_8/ZnS/C复合材料结构和形貌等进行表征,同时对片状Co_9S_8/ZnS/C复合材料进行了电催化产氧性能测试。结果表明:片状Co_9S_8/ZnS/C复合材料的起始过电位为390 mV,塔菲尔斜率为144 mV·dec~(-1),具有高的电催化产氧性能。  相似文献   

7.
In the Ca-Co-Zn-O system, we have determined the tie-line relationships and the thermoelectric properties, solid solution limits, and structures of two low-dimensional cobaltite series, Ca3(Co, Zn)4O9−z and Ca3(Co,Zn)2O6−z at 885 °C in air. In Ca3(Co,Zn)4O9−z, which has a misfit layered structure, Zn was found to substitute in the Co site to a limit of Ca3(Co3.8Zn0.2)O9−z. The compound Ca3(Co,Zn)2O6−z (n=1 member of the homologous series, Can+2(Co,Zn)n(Co,Zn)′O3n+3−z) consists of one-dimensional parallel (Co,Zn)2O66− chains that are built from successive alternating face-sharing (Co,Zn)O6 trigonal prisms and ‘n’ units of (Co,Zn)O6 octahedra along the hexagonal c-axis. Zn substitutes in the Co site of Ca3Co2O6 to a small amount of approximately Ca3(Co1.95Zn0.05)O6−z. In the ZnO-CoOz system, Zn substitutes in the tetrahedral Co site of Co3O4 to the maximum amount of (Co2.49Zn0.51)O4−z and Co substitutes in the Zn site of ZnO to (Zn0.94Co0.06)O. The crystal structures of (Co2.7Zn0.3)O4−z, (Zn0.94Co0.06)O, and Ca3(Co1.95 Zn0.05)O6−z are described. Despite the Ca3(Co, Zn)2O6−z series having reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical resistivity values of its members are too high to achieve high figure of merit, ZT.  相似文献   

8.
Single crystals of Ca3CuRhO6, Ca3Co1.34Rh0.66O6 and Ca3FeRhO6 were synthesized by high temperature flux growth in molten K2CO3 and structurally characterized by single crystal X-ray diffraction. While Ca3Co1.34Rh0.66O6 and Ca3FeRhO6 crystallize with trigonal (rhombohedral) symmetry in the space group , Z=6: Ca3Co1.34Rh0.66O6a=9.161(1) Å, c=10.601(2) Å; Ca3FeRhO6a=9.1884(3) Å, c=10.7750(4) Å; Ca3CuRhO6 adopts a monoclinic distortion of the K4CdCl6 structure in the space group C2/c, Z=4: a=9.004(2) Å, b=9.218(2) Å, c=6.453(1) Å, β=91.672(5). All crystals of Ca3CuRhO6 examined were twinned by pseudo-merohedry. Ca3CuRhO6, Ca3Co1.34Rh0.66O6, and Ca3FeRhO6 are structurally related and contain infinite one-dimensional chains of alternating face-sharing RhO6 octahedra and MO6 trigonal prisms. In the monoclinic modification, the copper atoms are displaced from the center of the trigonal prism toward one of the rectangular faces adopting a pseudo-square planar configuration. The magnetic properties of Ca3CuRhO6, Ca3Co1.34Rh0.66O6, and Ca3FeRhO6 are discussed.  相似文献   

9.
The two crystallographically non-equivalent Co atoms of the quasi-one-dimensional crystal structure of Ca3Co2O6 form chains with alternating, face-sharing polyhedra of Co2O6 trigonal prisms and Co1O6 octahedra. This compound forms a substitutional solid-solution phase with Sc, in which the Sc atoms enter the Co2 sublattice exclusively. The homogeneity range of Ca3Co2−vScvO6 (more specifically Ca3Co1Co21−vScvO6) extends up to v≈0.55. The crystal structure belongs to space group Rc with lattice parameters (in hexagonal setting): 9.0846(3)?a?9.1300(2) Å and 10.3885(4)?c?10.4677(4) Å. The magnetic moment decreases rapidly with increasing amount of the non-magnetic Sc solute in the lattice.  相似文献   

10.
The calcium cobalt oxide CaCo2O4 was synthesized for the first time and characterized from a powder X-ray diffraction study, measuring magnetic susceptibility, specific heat, electrical resistivity, and thermoelectric power. CaCo2O4 crystallizes in the CaFe2O4 (calcium ferrite)-type structure, consisting of an edge- and corner-shared CoO6 octahedral network. The structure of CaCo2O4 belongs to an orthorhombic system (space group: Pnma) with lattice parameters, a=8.789(2) Å, b=2.9006(7) Å and c=10.282(3) Å. Curie-Weiss-like behavior in magnetic susceptibility with the nearly trivalent cobalt low-spin state (Co3+, 3d, S=0), semiconductor-like temperature dependence of resistivity (ρ=3×10−1 Ω cm at 380 K) with dominant hopping conduction at low temperature, metallic-temperature-dependent large thermoelectric power (Seebeck coefficient: S=+147 μV/K at 380 K), and Schottky-type specific heat with a small Sommerfeld constant (γ=4.48(7) mJ/Co mol K2), were observed. These results suggest that the compound possesses a metallic electronic state with a small density of states at the Fermi level. The doped holes are localized at low temperatures due to disorder in the crystal. The carriers probably originate from slight off-stoichiometry of the phase. It was also found that S tends to increase even more beyond 380 K. The large S is possibly attributed to residual spin entropy and orbital degeneracy coupled with charges by strong electron correlation in the cobalt oxides.  相似文献   

11.
Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67(Ca0.65Ba0.35)0.33MnO3 and xPd-La0.67(Ca0.65Ba0.35)0.33MnO3 (abbreviated by xAg-LCBMO and xPd-LCBMO) composites. Both Pd and Ag addition induce a decrease in resistivity and an increase in temperature at which the resistivity reaches its maximum. This is mainly due to the improvement of grain boundaries caused by the segregation of good conductive metal grains on the grain boundaries/surfaces. In addition, both Pd and Ag addition induce a large enhancement of room temperature magnetoresistance (RTMR). Note that 27% molar ratio of Ag addition induces a large RTMR of about 70%, about ten times larger than pure LCBMO, whereas 27% molar ratio Pd addition brings a much larger RTMR of about 170%. The large enhancements of MR can be attributed to the decrease in resistivity of the samples caused by the good conductive metal. On the other hand, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries plays a very im-portant role in the increase in MR, which induces a large number of spin clusters in Pd-added samples.  相似文献   

12.
The new mixed oxide having composition close to Ca7Co3Ga5O18 was synthesized from CaCO3, Co3O4 and Ga2O3 at 1150 °C in air and studied by neutron and synchrotron X-ray powder diffraction, selected-area electron diffraction and high-resolution electron microscopy. The structure was refined, using time-of-flight (TOF) neutron powder diffraction data, in space group F432, with and Z=8, to RF=0.7%. It is considerably disordered, with four different tetrahedral sites randomly occupied by Co and Ga atoms at a ratio of 1:2. The tetrahedra form a disordered (Co1/3Ga2/3)O2 3D-framework inside which isolated CoO6 octahedra, surrounded by 8 Ca atoms, are located. The structure is related to the ordered structure of Ca14Al10Zn6O35. Electron diffraction patterns confirmed the symmetry and unit cell and revealed no diffuse scattering. High-resolution electron microscopy images showed the absence of extended structural defects.  相似文献   

13.
A new complex oxide with the cation ratio Ca:Co: Ga=2:0.8:1.2 has been synthesized in air at 1150oC. The cobalt atoms adopt oxidation states 2+ and 3+ in equal amounts giving an oxygen content corresponding to the composition Ca2Co0.8Ga1.2O4.8. It crystallizes in F-centered cubic structure with a=15.0558 Å. Conductivity measurements performed at high temperatures revealed that the temperature increase gives a charge disproportionation of Co3+ species resulting in a small concentration of Co4+ species and thus a small p-type conductivity in the oxide. A decrease of the oxygen pressure promotes oxygen depletion from the oxide and a deterioration of the conductivity. The electric properties are interpreted within a small polaron conduction mechanism. An unusually large mobility activation energy of 0.45 eV can be explained by a large spatial separation of cobalt cations in the structure.  相似文献   

14.
张霞  陈莉  周春彬 《无机化学学报》2010,26(11):1934-1938
借助于PANI的还原性质,PANI/Fe2O3复合载体与AgNO3发生表面氧化还原反应,合成了Ag/PANI/Fe2O3复合纳米粒子。TEM和XRD结果表明,立方晶系纳米银的平均粒径10nm。FTIR结果表明,Ag与PANI及Fe2O3复合载体之间不存在化学键合作用,但由于PANI与Ag之间的电子相互作用,Ag/PANI/Fe2O3复合纳米粒子的FTIR吸收峰发生蓝移。Ag/PANI/Fe2O3复合纳米粒子对于间硝基苯磺酸钠的硼氢化钠还原反应表现出良好的催化活性,30min内间硝基苯磺酸钠的转化率达到86.77%。  相似文献   

15.
The effects of doping cobalt oxides with different amounts of ZrO2 and ThO2 (1.5–9 mol%) on the thermal stability of Co3O4 and the re-oxidation of CoO by O2 to Co3O4 were investigated. The techniques employed were DTA, with a controlled rate of heating and cooling, X-ray diffraction, and IR spectrometry.The results obtained by DTA revealed that the addition of both Th4+ and Zr4+ (up to 6 mol%) exerted no appreciable effect on the thermal stability of Co3O4. Increasing the amount of the dopant ions to 9% resulted in no further change in the thermal stability of Co3O4 in the case of Th4+, and an increase of 16% in case of Zr4+-doping. However, ThO2-doping of cobalt oxide was accompanied by an enhancement in the reactivity of CoO towards re-oxidation by O2 to Co3O4 to an extent proportional to the amount of dopant oxide.The X-ray investigation of ZrO2-doped cobalt oxides calcined in air at 1000°C revealed the presence of highly crystalline and stable zirconia in the cubic form. Such a stable phase could not be obtained at temperatures below 2370°C in the absence of stabilizing agents.X-ray and IR investigations of different solids showed the presence of free thoria and zirconia together with new thorium—cobalt and zirconium—cobalt compounds. However, the slow cooling of Zr-treated cobalt oxides from 1000°C to room temperature led to the decomposition of the newly formed compound. The d-spacings and absorption bands of the newly formed compounds were determined.  相似文献   

16.
A series of bulk polycrystalline La0.7Ca0.2Sr0.1MnO3 (LCSMO)-Ag composites were prepared by electroless plating process and several kinds of physical properties have been studied systemically. According to the results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electromagnetic transport properties, we can see that Ag-added segregated at the surfaces or interfaces of LCSMO grains. The metal-insulator transition temperature (TP) and Curie temperature (Tc) were almost unchanged but ρ decreased with increasing plating time. We also observed Ag-added can significantly enhance the magnetoresistance (MR) near TP under a low applied field (3000 Oe) and the room temperature MR reached to 35% under 20 kOe, which is encouraging for practical applications. We can suggest that improved grain boundary effect by Ag-added is responsible for the enhancement.  相似文献   

17.
Electrolysis of suspensions of Co3O4 particles in Pb2+-containing electrolytes has been used for depositing PbO2 + Co3O4 composite layers on Ni rotating dise anodes. A sufficiently high angular speed of the electrode is necessary to obtain layers of homogeneous thickness and Co3O4 concentration. The volume fraction of Co3O4 particles in the deposit α reaches a limiting value of ca. 0.1 when the volume fraction of particles in suspension C exceeds 0.008. The current density j has little effect on α as long as it is in the range 1 to 20 mA cm−2; if j increases further, α decreases.PbO2 + Co3O4 composite layers have been studied as electrode materials for the oxygen evolution reaction (mainly in NaOH solution). The overpotential and Tafel slope decrease upon increasing α. At a fixed potential, j is roughly proportional to OH concentration. The PbO2 + Co3O4 electrode performance is fairly stable at 25°C but declines with time at higher temperature.  相似文献   

18.
Granular Ag-added La0.7Ca0.3MnO3 (LCMO) samples were prepared by a sol-gel chemical route. Significant enhancements in Curie temperature (TC), metal−insulator transition (Tp) and magnetoresistance (MR) effects near room temperature are observed in as-obtained samples. 10 wt% addition of Ag in LCMO causes TC shift from 272 to 290 K, Tp boost up for more than 100 K and resistivity decrease by more than 3 orders of magnitude. X-ray diffraction patterns, thermal analysis and energy dispersive analysis of X-rays evidently show the existence of metal silver in LCMO matrices. High-resolution electron microscopy illustrates a well crystallization for LCMO grains in existence of Ag. It is argued that improved grain boundary effect and better crystallization caused by Ag addition are responsible for the enhancements.  相似文献   

19.
Substitution of Li+ into Co3O4 and ZnCo2O4 gives rise to the solid solution series LixM1?xCo2O4 (M = Co2+ or Zn2+) having the spinel structure upto x = 0.4. X-Ray diffraction intensities show that the spinel solid solutions are likely to have the following cation distributions: (Co2+)t[Li+xCo3+2?3xCo4+2x]0O4 and (Zn2+1?xCo2+x)t[Li+xCo3+2?3xCo4+2x]0O4. Electrical resistivity and Seebeck coefficient data indicate that the electron transport in these systems occurs by a small-polaron hopping mechanism.  相似文献   

20.
Two new potassium uranyl molybdates K2(UO2)2(MoO4)O2 and K8(UO2)8(MoO5)3O6 have been obtained by solid state chemistry . The crystal structures were determined by single crystal X-ray diffraction data, collected with MoKα radiation and a charge coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least square method on the basis of F2 for all unique reflections, with R1=0.046 for 136 parameters and 1412 reflections with I?2σ(I) for K2(UO2)2(MoO4)O2 and R1=0.055 for 257 parameters and 2585 reflections with I?2σ(I) for K8(UO2)8(MoO5)3O6. The first compound crystallizes in the monoclinic symmetry, space group P21/c with a=8.250(1) Å, b=15.337(2) Å, c=8.351(1) Å, β=104.75(1)°, ρmes=5.22(2) g/cm3, ρcal=5.27(2) g/cm3 and Z=4. The second material adopts a tetragonal unit cell with a=b=23.488(3) Å, c=6.7857(11) Å, ρmes=5.44(3) g/cm3, ρcal=5.49(2) g/cm3, Z=4 and space group P4/n.In both structures, the uranium atoms adopt a UO7 pentagonal bipyramid environment, molybdenum atoms are in a MoO4 tetrahedral environment for K2(UO2)2(MoO4)O2 and MoO5 square pyramid coordination in K8(UO2)8(MoO5)3O6. These compounds are characterized by layered structures. The association of uranyl ions (UO7) and molybdate oxoanions MoO4 or MoO5, give infinite layers [(UO2)2(MoO4)O2]2− and [(UO2)8(MoO5)3O6]8− in K2(UO2)2(MoO4)O2 and K8(UO2)8(MoO5)3O6, respectively. Conductivity properties of alkali metal within the interlayer spaces have been measured and show an Arrhenius type evolution.  相似文献   

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