Thermoelectric properties and electronic structure of p-type Mg2Si and Mg2Si0.6Ge0.4 compounds doped with Ga

Mg₂Si:Ga_x and Mg₂Si_0.6Ge_0.4:Ga_x (x = 0.4% and 0.8%) solid solutions have been synthesized by direct melting in tantalum crucibles and hot pressing. The effect of Ga doping on the thermoelectric properties has also been investigated by measurements of thermopower, electrical resistivity, Hall coefficient and thermal conductivity in temperature range from 300 to 850 K. All samples exhibit a p-type conductivity evidenced by positive sign of both thermopower and Hall coefficient in the investigated temperatures. The maximum value of the dimensionless figure of merit ZT was reached for the Mg₂Si_0.6Ge_0.4:Ga(0.8%) compound at 625 K (ZT ∼ 0.36). The p-type character of thermoelectric behaviours of Ga-doped Mg₂Si and Mg₂Si_0.6Ge_0.4 compounds well corroborates with the results of electronic structure calculations performed by the Korringa-Kohn-Rostoker method and the coherent potential approximation (KKR-CPA), since Ga diluted in Mg₂Si and Mg₂Si_0.6Ge_0.4 (on Si/Ge site) behaves as hole donor due to the Fermi level shifted to the valence band edge. The onset of large peak of DOS from Ga impurity at the valence band edge, well corroborates with high Seebeck coefficient measured in Ga-doped samples.     

不同方法合成的LiVPO4F/C的电化学性能（英文）

通过一步固相反应和两步固相反应分别合成LiVPO4F/C,采用XRD、SEM和电化学性能测试对LiVPO4F/C进行性能表征。XRD研究表明一步固相反应合成的LiVPO4F/C与两步固相反应合成的样品一样,均属于三斜晶系结构。SEM研究表明:一步固相反应合成的LiVPO4F/C颗粒比两步固相反应合成的样品颗粒小,一步固相反应合成的 LiVPO4F/C 样品电化学性能得到提高是由于草酸作为还原剂和碳源合成的样品颗粒变小。交流阻抗研究表明步固相反应合成的LiVPO4F/C样品电化学阻抗减小。     

Studies on the one-dimensional platinum atom chain compound Rb3(H3O)0.2[Pt(CN)4](O3SO·H·OSO3)0.5·0.8H2O

The variation of conductivity and thermopower with temperature for Rb₃(H₃O)_0.2[Pt(CN)₄](O₃SO·H·OSO₃)_0.5·0.8H₂O is reported. The abrupt falls in conductivity at low temperature previously reported have been carefully studied and from the non-reproducible nature of the phenomena, it is deduced that these result from cracks in the sample rather than a phase change in the material.     

Magnetic microstructure and the electrical properties of rare-earth Fe-substituted cuprates of the 8-8-20 type

Crystal structure, magnetic microstructure, and electrical properties of cuprates of rare-earth elements with a partial substitution of the atoms of strontium for rare-earth elements (REEs) and iron for copper have been investigated. The detailed analysis of the Mössbauer spectra of cuprates made it possible to assume that the substitution of strontium for REEs in iron-substituted cuprates of neodymium leads to a recharging of part of iron cations, and in praseodymium cuprates, of lanthanide ions. The measurements of electrical conductivity and thermopower of the samples confirmed this assumption.     

Synthesis and characteristics of poly(3-pyrrol-1-ylpropanoic acid) (PPyAA)-Fe3O4 nanocomposite

Poly(3-pyrrol-1-ylpropanoic acid) (PPyAA)-Fe₃O₄ nanocomposite was successfully synthesized by an in situ polymerization of 1-(2-carboxyethyl) pyrrole in the presence of synthesized Fe₃O₄ nanoparticles. Evaluation of structural, morphological, electrical and magnetic properties of the nanocomposite was performed by XRD, FT-IR, TEM, TGA, magnetization and conductivity measurements, respectively. XRD analysis reveals the inorganic phase as Fe₃O₄ and TGA shows about 90 wt% loading of Fe₃O₄ in the nanocomposite. FT-IR analysis indicates a successful conjugation of Fe₃O₄ particles with polypyrrole acetic acid. Magnetization measurements show that polypyrrole acetic acid coating decreases the saturation magnetization of Fe₃O₄ significantly. This reduction has been explained by the pinning of the surface spins by the possible adsorption of non-magnetic ions during the polymerization process. The conductivity and dielectric permittivity measurements strongly depend on the thermally activated polarization mechanism and thermal transition of PPyAA in the nanocomposite structure. Large value of dielectric permittivity (?′) of the nanocomposite at lower frequency is attributed to the predominance of species like Fe²⁺ ions and grain boundary defects (interfacial polarization).     

Thermoelectric properties of rare-earth alloys

The electrical resistivity, thermal conductivity, and thermopower have been measured for a large number of newly synthesized metallic compounds and alloys of simple, transition, and rare-earth elements. The maximum room-temperature values of the thermoelectric figure of merit ZT for the presented systems are about 7%. The temperature dependences of the resistivity and thermoelectric power have been discussed. Particular attention has been given to possible manifestations of the Kondo effect and intermediate valence including those in systems based on silicides and nickelides of cerium.     

氢气流量对大气等离子喷涂TiO2涂层导电性的影响

采用大气等离子喷涂方法制备TiO2涂层,研究氢气流量的变化对TiO2涂层的显微结构、相结构以及导电性的影响.随着氢气流量的增加,TiO2涂层的孔隙率减少,缺氧相增加,涂层的电阻率随之减小.同时在通电升温条件下涂层的电导率随温度的升高而增加.结果表明,大气等离子喷涂TiO2涂层主要由金红石相、锐钛矿相和缺氧相Magneli(TinO2n-1,n=4～10)组成,各相的含量与等离子气中氢气的流量有关.     

Microstructures and properties of rapidly solidified Cu90Zr10-xAlx alloys

Cu_(90)Zr_(10-x)Al_x(x=1, 3, 5, 7, 9; at.%) alloy rods were synthesized based on rapid solidification method. The structure, distribution of elements, mechanical properties and electrical conductivity of the Cu-based alloy samples were studied using X-ray diffraction(XRD), scanning electron microscope(SEM), electro-probe micro-analyzer(EPMA), uniaxial compression test and four-probe technique. The as-cast Cu_(90)Zr_(10-x)Al_x(x=1, 3, 5; at.%) alloy rods with a diameter of 2 mm exhibit good mechanical properties and electrical conductivity, i.e., high compressive yield strength of 812-1513 MPa, Young's modulus of 52-85 GPa, Vickers hardness of 250-420 and electrical conductivity of 11.1%-12.6% IACS(International Annealed Copper Standard). The composite microstructure composed of high density fibrous duplex structure(Cu_5Zr and α-Cu phases) is thought to be the origin of the high strength.     

High-pressure low-temperature electrical properties of polypyrrole doped with p-toluenesulfonate

The electrical properties of polypyrrole doped with p-toluenesulfonate are investigated at temperatures from 300 to 1.2 K and pressures up to 2 GPa. A linear temperature dependence of the thermopower below 150 K supports the intrinsic metallic nature of the samples. The electrical conductivity shows the crossover from nearest-neighbour hopping to variable range hopping at low temperatures. Application of pressure results in a remarkable decrease of the localization strength of the charge carriers and a weaker temperature dependence of the conductivity.     

Transport properties of the YbAl3 compound: On the energy scales of YbAl3 from thermopower data

We report thermopower and resistivity measurements of an YbAl₃ single crystal obtained by the “self-flux” method. Our data reveal Fermi liquid behavior up to T_FL = 35 K. The Kondo temperature, T_K ≈ 450 K, was determined from the high temperature thermopower data. The characteristic temperature, T₀, extracted from the temperature slope of the thermopower in the Fermi liquid regime is higher than the T_K. We discuss a possible explanation of the obtained energy scales of YbAl₃.     

XPS and electrical characterization of BF4−-doped polypyrrole exposed to oxygen and water

X-ray photoelectron spectroscopy and conductivity measurements have been used to investigate electrochemically prepared, BF₄^?-doped, polypyrrole. The effects of storage in atmospheres containing water and oxygen, as well as exposure to liquid water have been studied specifically. The results show that the concentration of the BF₄^? anion originally incorporated in the polymer decreases upon storage, irrespective of the composition of the storage atmosphere. A strong synergetic effect of oxygen and water vapour is observed, which results in a large increase in the rate at which the conductivity is degraded. In the case of exposure to liquid water, it is observed that oxygen dissolved in the water strongly enhances the degradation of the electrical conductivity. The N(1s) core-level spectra show specifically that PPy(BF₄^?) is modified by treatment with oxygen-saturated water in a similar way to that observed earlier after treatment with NaOH solution. The XPS results are interpreted as a deprotonation of the pyrrole nitrogen simultaneous with a rearrangement of the conjugation pattern of the aromatic polymer chain.     

La2O3含量对Al2O3/Cu基复合材料组织与性能的影响

以La₂O₃粉、Al粉、CuO粉为反应物原料、纯铜为基体,采用原位合成技术和近熔点铸造法制备颗粒增强Cu基复合材料,研究La₂O₃对Al-CuO体系制备的Cu基复合材料组织及性能的影响。结果表明：添加La₂O₃可获得纳米Al₂O₃颗粒,且弥散分布于Cu基体中,制备的材料组织更加细小、均匀,其材料的电导率及摩擦磨损性能明显提高。当添加0.6%wtLa₂O₃,复合材料的电导率达到90.2%IACS,磨损量达到最小,相比未添加La₂O₃,其导电率提高10.1%,磨损量减小36.6%。     

不同Ce含量的Nd_(2-x)Ce_xCuO_4(x=0.14,0.15)单晶的输运性质

通过对电子型超导体Nd2-xCexCuO4(x=0.14,0.15)单晶ab面电阻率、热电势及热导的研究,发现x=0.14样品的热电势在42K附近变号,而x=0.15的热电势在整个温区都是正值,但在高温区两个样品的热电势都呈现负斜率,此现象只能归因于系统中同时存在一个电子型的能带和一个空穴型的能带。而且其电阻率行为也能用双能带模型很好的解释。随着x增加,高温区热导增加而低温区的声子峰被压低,表明载流子对热导的贡献在增加,同时声子的散射也在增加。     

Sm0.5Sr0.5CoO3 cathode material from glycine-nitrate process: Formation, characterization, and application in LaGaO3-based solid oxide fuel cells

Cathode material Sm_0.5Sr_0.5CoO₃ (SSC) with perovskite structure for intermediate temperature solid oxide fuel cell was synthesized using glycine-nitrate process (GNP). The phase evolution and the properties of Sm_0.5Sr_0.5CoO₃ were investigated. The single cell performance was also tested using La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolyte and SSC as cathode. The results show that the formation of perovskite phase from synthesized precursor obtained by GNP begins at a calcining temperature of 600 °C. The single perovskite phase is formed completely after sintering at a temperature of 1000 °C. The phase formation temperature for SSC with complete single perovskite phase is from 1000 to 1100 °C. The SrSm₂O₄ phase appeared in the sample sintered at 1200 °C. It is also found that the sample sintered at 1200 °C has a higher conductivity. The electrical conductivity of sample is higher than 1000 S/cm at all temperature examined from 250 to 850 °C, and the highest conductivity reaches 2514 S/cm at 250 °C. The thermal expansion coefficient of sample SSC is 22.8 × 10⁻⁶ K⁻¹ from 30 to 1000 °C in air. The maximum output power density of LSGM electrolyte single cell attains 222 and 293 mW/cm² at 800 and 850 °C, respectively.     

Synthesis, characterization and electrical properties of CdI2 doped Al2O3 and TiO2 superionic conductors

Superionic conductors were prepared by admixing metallic oxides (alumina and titania) with cadmium iodide in different proportions using direct mixing method. The synthesized materials were characterized by various qualitative techniques such as XRD (X-ray diffraction), DSC (differential scanning calorimetry) and SEM (scanning electron microscopy). Pure CdI₂ shows the standard pattern which corresponds to β-phase stable at room temperature, however, the diffractograms of the mixtures shows two phase nature of the materials with no effect of the second phase on the peak positions of the first, i.e. CdI₂. DSC curves also confirmed the formation of composite. SEM micrographs show the presence of great number of space charge regions which are very important in creating a great number of surfaces which in turn act as additional sources of point defects. It was also found that the conductivity of CdI₂ increases with mole fractions of dopants till x = 0.5 for alumina and x = 0.3 for titania. Arrhenius equation was used to study the temperature dependence of electrical conductivity and the activation energy of pure cadmium iodide was found to be 0.792 eV.     

Thermoelectric properties of semi-conducting compound Zn4Sb3

Hot-pressed samples of the semi-conducting compound Zn₄Sb₃ with the stoichiometric composition were prepared and characterized by X-ray and microprobe analysis. Thermoelectric characterization was done through measurements of the electrical and thermal conductivities as well as the Seebeck coefficient between room temperature and 650 K. All samples had p-type conductivity. High thermoelectric figures of merit (ZT) were obtained between 450 and 650 K and a maximum of about 1.3 were obtained at a temperature of 650 K.     

Dielectric relaxation and conduction mechanism in LaNi3/4M1/4O3 (M = Mo, W) at low temperature

In order to investigate the electrical transport in LaNi_3/4Mo_1/4O₃ and LaNi_3/4W_1/4O₃, the dc conductivity and dielectric properties in these polycrystalline materials are investigated in the temperature range from 163 K to 383 K and frequency range from 50 Hz to 1 MHz. The X-ray diffraction patterns of the samples show monoclinic phase at room temperature. The homogeneity of the samples is determined by energy dispersive analysis of X-ray (EDAX) attached with a scanning electron microscope. The temperature dependence of dc conductivity shows the semiconducting nature of the materials. The complex impedance plane plots show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The frequency-dependent electrical data are also analyzed in the framework of ac conductivity formalism. The ac conductivity spectra follow the universal power law. The activation energies required for bulk conduction is 0.143 and 0.165 eV for LNM and LNW respectively. The scaling behaviour of loss tangent suggests that the relaxation describes the same mechanism at various temperatures.     

Preparation of polyaniline–titanium dioxide hybrid materials in supercritical CO2

Polyaniline–titanium dioxide (PANI–TiO₂) hybrid materials were synthesized in supercritical CO₂ using two different methods. In the first method, separately synthesized TiO₂ particles were mixed with aniline to perform polymerization in supercritical CO₂. The second method included the preparation of aniline–TiO₂ hybrids through a sol–gel reaction of titanium isopropoxide in the presence of aniline. Further polymerization of aniline–TiO₂ hybrids in supercritical CO₂ produced PANI–TiO₂ hybrid particles. The final products showed the intrusion of PANI into the internal structure of TiO₂. The PANI–TiO₂ hybrid materials were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), electrical conductivity (EC), Fourier-transform infrared (FT-IR) and X-ray diffraction (XRD) measurements. PANI–TiO₂ nano-composites synthesized with the first method showed a relatively low electrical conductivity of 3.78 × 10⁻² S/cm at 20 °C. TGA suggested that the particles contained 40.6% TiO₂ by mass and showed a strong interaction at the interface of TiO₂ and PANI. The electrical conductivity of the hybrid particles produced using the second method increased to 7.75 × 10⁻² S/cm and the TGA results showed 34.4% TiO₂ by mass. Through SEM and TEM analyses it was confirmed that the PANI has been interpenetrated into the three-dimensional network of the TiO₂ when the second method was used.     

The electrical conductivity and microstructure properties of Ni-doped TiO2 ceramic

The electrical, microstructure and crystal structure properties of Ni-doped TiO₂ were investigated. The microstructure and crystal structure of Ni-doped TiO₂ were analyzed by the scanning electron microscopy and X-ray diffraction techniques. The alternating conductivity (AC) and direct current conductivity (DC) properties of Ni-doped TiO₂ have been investigated. DC conductivity exhibits a semiconductor behavior with the temperature. AC and DC measurements suggest that variable-range hopping (VRH) conduction is dominated by hopping of carriers between localized states at lower temperatures. At higher temperatures, the conduction mechanism of the sample is constant-range hopping charge transport.     

Electrical Properties of Atmospheric Plasma-Sprayed La10(SiO4)6O3 Electrolyte Coatings

In this present work, La₁₀(SiO₄)₆O₃ as a promising electrolyte candidate for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been synthesized and its electrical property was investigated as a function of temperature. In order to improve the density and oxide ion conductivity of La₁₀(SiO₄)₆O₃, the feedstock powder was prepared by sintering the oxide mixture powders at proper sintering temperatures and times. The hexagonal apatite-type ceramic coatings with a typical composition of La₁₀(SiO₄)₆O₃ were deposited by atmospheric plasma spraying (APS) with different hydrogen flow rates. With increasing hydrogen flow rate oxide ion conductivity successively decreases. The highest ionic conductivity of the dense composite electrolyte coatings reaches a value of 2.4 mS/cm at 900 °C in air, which is comparable to other apatite-type lanthanum silicate (ATLS) conductors.