Electronic transport properties of Te-doped CoSb<Subscript>3</Subscript> skutterudites prepared by hot pressing

Te-doped CoSb₃ (CoSb_3−yTe_y) skutterudites were prepared by hot pressing and their electronic transport properties examined. A single δ-phase was successfully obtained. The Seebeck and Hall coefficients confirmed that all the Te-doped CoSb₃ showed n-type conduction. The Te atoms successfully acted as electron donors by substitution of the Sb atoms. The carrier concentration increased an order of 10²⁰ cm⁻³ by Te doping, whereas the carrier mobility decreased as the doping content increased. The Seebeck coefficient and electrical resistivity decreased with an increase in the Te content. The doping considerably reduced the thermal conductivity due to electron-phonon scattering. The lattice contribution was dominant over the electronic contribution.     

Surface modification of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> with Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> for lithium ion batteries

Cr 2 O 3-coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials were synthesized by a novel method. The structure and electrochemical properties of prepared cathode materials were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The measured results indicate that surface coating with 1.0 wt% Cr 2 O 3 does not affect the LiNi 1/3 Co 1/3 Mn 1/3 O 2 crystal structure (α-NaFeO 2 ) of the cathode material compared to the pristine material, the surfaces of LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples are covered with Cr 2 O 3 well, and the LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with Cr 2 O 3 has better electrochemical performance under a high cutoff voltage of 4.5 V. Moreover, at room temperature, the initial discharging capacity of LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with 1.0 wt.% Cr 2 O 3 at 0.5C reaches 169 mAh·g 1 and the capacity retention is 83.1% after 30 cycles, while that of the bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 is only 160.8 mAh·g 1 and 72.5%. Finally, the coated samples are found to display the improved electrochemical performance, which is mainly attributed to the suppression of the charge-transfer resistance at the interface between the cathode and the electrolyte.     

Effects of Sc doping on electrical conductivity of BaZrO<Subscript>3</Subscript> protonic conductors

BaZr1-xScxO3-0.5x (x=0.07,0.10,0.13,0.16) powders were prepared by solid-state reaction method,and ZnO was used as sintering aid.Samples with different amount of ZnO additive were sintered at 1450 ℃ for 6 h in air.Single cubic perovskite phase proton conductors were obtained.Conductivity was measured by electrochemical workstation.It was shown that Sc doping could increase conductivity through enhancing the carrier concentration in the material,but excessive Sc content might decrease the carrier concentration because of its charge compensation.ZnO had an influence on carrier concentration and mobility and affected the electrical conductivity.2 mol％ ZnO and 13 mol％ ScO1.5 doped sample showed the highest DC conductivity of 3.6 × 10-3 S·cm-1 tested at 800 ℃ in wet hydrogen atmosphere.     

Enhancement of room-temperature magnetoresistance in La<Subscript>0.6</Subscript>Dy<Subscript>0.1</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The samples of La0.6Dy0.1Sr0.3MnO3/(Ag2O)x/2(x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.25, and 0.30) were prepared by using the solid-state reaction method.Their magnetic property, transport behavior, transport mechanism and magnetoresistance effect were studied through the measurements of magnetization-temperature(M-T) curves, ρ-T curves and the fitting of ρ-T curves.The results indicated that Ag could take part in the reaction when the doping amount is small.However, when the doping amount is compar...     

Electrochemical properties of carbon-coated LiFePO<Subscript>4</Subscript> and LiFe<Subscript>0.98</Subscript>Mn<Subscript>0.02</Subscript>PO<Subscript>4</Subscript> cathode materials synthesized by solid-state reaction

Olivine structured LiFePO4/C (lithium iron phosphate) and Mn2+-doped LiFe0. 98Mn0. 024/C powders were synthesized by the solid-state reaction. The effects of manganese partial substitution and different carbon content coating on the surface of LiFePO4 were considered. The structures and electrochemical properties of the samples were measured by X-ray diffraction (XRD), cyclic voltammetry (CV), charge/discharge tests at different current densities, and electrochemical impedance spectroscopy (EIS). The electrochemical properties of LiFePO4 cathodes with x wt. ％ carbon coating (x=3, 7, 11, 15) at γ=0. 2C, 2C (1C=170 mAh·g-1) between 2. 5 and 4. 3 V were investigated. The measured results mean that the LiFePO4 with 7 wt. ％ carbon coating shows the best rate performance. The discharge capacity of LiFe0. 98Mn0. 02PO4/C composite is found to be 165 mAh·g 1 at a discharge rate, γ=0. 2C, and 105 mAh·g-1 at γ=2C, respectively. After 10cycles, the discharge capacity has rarely fallen, while that of the pristine LiFePO4/C cathode is 150 mAh·g-1 and 98 mAh·g-1 at γ=0. 2 and 2C, respectively. Compared to the discharge capacities of both electrodes above, the evident improvement of the electrochemical performance is observed, which is ascribed to the enhancement of the electronic conductivity and diffusion kinetics by carbon coating and Mn2+-substitution.     

Effect of yttrium doping on the resistivity and magnetoresistance of La<Subscript>0.80</Subscript>Sr<Subscript>0.20</Subscript>MnO<Subscript>3</Subscript>

The temperature and magnetic field dependence of resistivity of crystals of nominal compositions of La_0.75Y_0.05Sr_0.20MnO₃ grown by floating zone method at different growth rates are studied. The yttrium doping is found to result in the decrease of Curie temperature, suppression of the Pnma-R $ \bar 3 $ \bar 3 c structural transition, increase of resistivity and magnetoresistance. It is shown that the physical properties of the manganites studied are determined by not only the nominal composition but also the growth rate.     

Magnetoresistive properties of Ni-doped La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> manganites

La_0.7Sr_0.3Mn_1?x Ni _x O₃ (x = 0, 0.025, 0.050 and 0.075) ceramics were prepared by the conventional solid-state reaction method. The partial substitution of Mn by Ni²⁺ leads to a decrease in cell volume as well as a structural transition from the rhombohedral to the orthorhombic structure. Ni²⁺ doping increases the electrical resistivity, decreases the semiconductor–metal transition temperature (T _ms) and relatively enhances the room temperature magnetoresistance (MR), especially in x = 0.025 and around T _ms. With respect to conduction mechanism, the small polaron hopping (SPH) and the variable range hopping (VRH) models were used to examine conduction in the semiconducting region.     

Dielectric properties of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films deposited onto Ti and TiO<Subscript>2</Subscript> layer

The present study describes the dielectric properties of RF sputtered Ta₂O₅ thin films as a function of the buffer layer and annealing condition. The buffer layers were Ti or TiO₂. And the thin film was annealed in various conditions. The X-ray pattern results showed that the phase of the RF sputtered Ta₂O₅ thin films was amorphous and this state was kept stable to RTA (rapid thermal annealing) even at 700°C. Measurements of the electrical and dielectric properties of the reactive sputtered Ta₂O₅ fabricated in two simple metal insulator semiconductor (MIS) structures, (Cu/Ta₂O₅/Ti/Si/Cu and Cu/Ta₂O₅/TiO₂/Si/Cu) indicated that the amorphous Ta₂O₅ grown on Ti possesses a high dielectric constant (30–70) and high leakage current (10⁻¹–10⁻⁴ A/cm²), whereas a relatively low dielectric constant (−10) and low leakage current (−10⁻¹⁰ A/cm²) were observed in the amorphous Ta₂O₅ deposited on the TiO₂ buffer layer. In addition, the leakage current mechanisms of the two amorphous Ta₂O₅ thin films were investigated by plotting the relation of current density (J) vs. applied electric field (E). The Ta₂O₅/Ti film exhibited three dominant conduction mechanism regimes contributed by the Ohmic emission at low electrical field, by the Schottky emission at intermediate field and by the Poole-Frenkel emission at high field. In the case of Ta₂O₅/TiO₂ film, the two conduction mechanisms, the Ohmic and Schottky emissions, governed the leakage current density behavior. The conduction mechanisms at various electric fields applied were related to the diffusion of Ta, Ti and O, followed by the creation of vacancies, in the rapid thermal treated capacitors.     

Comparative analysis of the kinetics of dissolution of oxides Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> in the iron matrix upon mechanical alloying

The kinetics of low-temperature dissolution of oxides Y₂O₃ and Fe₂O₃ in an iron matrix during mechanical alloying has been studied using electron microscopy. It has been shown that the dissolution rate upon deformation of primary coarse oxides Fe₂O₃ in α iron (and, hence, saturation of the α matrix with oxygen) during treatment in a ball mill for up to 10 h is several times higher than the dissolution rate of Y₂O₃ oxides. The high-temperature (1100°C) annealing of a mechanoalloyed mixture of Fe + 1.5% Y + 1.35% Fe₂O₃ leads to the precipitation of 60% (of the total number of particles) secondary oxides 2–5 nm in size and only of 5–7% secondary nanooxides in a mechanoalloyed mixture of Fe + 2% Y₂O₃.     

Solvothermal synthesis and thermoelectric properties of skutterudite compound Fe（0.25）Ni（0.25）Co（0.5）Sb3

Nanostructured skutterudite-related compound Fe_0.25Ni_0.25Co_0.5Sb₃ was synthesized by a solvothermal method using FeCl₃, NiCl₂, CoCl₂, and SbCl₃ as the precursors and NaBH₄ as the reductant. The solvothermally synthesized powders consisted of fine granules with an average particle size of tens of nanometers. The bulk material was prepared by hot pressing the powders. Transport property measurements indicated a heavily doped semiconductor behavior with n-type conduction. The thermal conductivity is about 1.83 W·m⁻¹·K⁻¹ at room temperature and decreases to 1.57 W·m⁻¹·K⁻¹ at 673 K. The low thermal conductivity is attributed to small grain size and high porosity. A maximum dimensionless figure of merit of 0.15 is obtained at 673 K.     

The distinct role of transition metal doping for LiFePO<Subscript>4</Subscript> cathode material

This study addresses the controversial issue of the effect of metal ion doping on the electrochemical performance of LiFePO₄. Metal doping is claimed to be a possible cause for the capacity improvement of LiFePO₄ as carbon coating. Results obtained inthis study show that dry-milled LiFePO₄ and LiFe_0.9Cr_0.1PO₄ deliver 119 mAh g⁻¹ and 101 mAh g⁻¹, while wet-milled LiFePO₄ and LiFe_0.9Cr_0.1PO₄ deliver 149 mAh g⁻¹ and 138 mAh g⁻¹, respectively. This indicates that the capacity improvement by metal doping is due to the carbonaceous materials produced during fabrication and not by the enhancement of ion diffusion. On the other hand, cycle test results show that metal doping enhances the rate capability at high C-rates by accelerating lithium ion diffusion.     

A new symmetric solid-oxide fuel cell with La0.8Sr0.2Sc0.2Mn0.8O3-δ perovskite oxide as both the anode and cathode

A novel perovskite-type La_0.8Sr_0.2Sc_0.2Mn_0.8O₃ (LSSM) oxide was synthesized and evaluated as the electrode material of a symmetric solid-oxide fuel cell. Characterization was done by electrical conductivity, crystal structure stability, redox stability, catalytic activity for methane oxidation and oxygen electro-reduction. LSSM shows greater electrical conductivity than the typical La_0.8Sr_0.2Cr_0.5Mn_0.5O₃ (LSCM) perovskite oxide under both anode and cathode operating conditions. It also shows excellent chemical and structural stability due to the backbone effect of Sc³⁺ for the perovskite lattice structure. A symmetric electrolyte-supported cell with 0.3 mm thick scandium-stabilized zirconia electrolyte and LSSM as cathode and anode shows peak power densities of 310 and 130 mW cm² at 900 °C, respectively, when operating on wet H₂ and wet CH₄. Stable performance is demonstrated.     

Electron-doped manganites based on CaMnO<Subscript>3</Subscript>

The work is devoted to a review of magnetic, electrical, and optical properties of electron-doped manganites Ca_{1 − x} Ln _x MnO₃ (Ln stands for rare-earth ions) at the concentrations of the doping ions x from 0 to 0.2. The main attention is paid to the data obtained using single crystals containing vacancies in both the anion and cation sublattices. The features of the multiphase state of the Ca_{1 − x} Ln _x MnO₃ manganites (x < 0.2) are discussed.     

Effects of Ce<Superscript>3+</Superscript> doping on the structure and magnetic properties of Mn-Zn ferrite fibers

Ce³⁺-doped Mn-Zn ferrite fibers were successfully prepared by the organic gel-thermal decomposition method from metal salts and citric acid. The composition, structure, and magnetic properties of these ferrite fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The results show that Mn_0.2Zn_0.8Fe_2−x Ce _x O₄ (x = 0–0.04) fibers are featured with an average grain size of 11.6–12.7 nm, with diameters ranging between 1.0 to 3.5 μm and a high aspect ratio (length/diameter). The Ce³⁺ ion doping has not resulted in crystal structural changes of the Mn-Zn ferrite phase and all the as-prepared ferrite fibers have a simple spinel phase structure, although this influences the morphologies of Mn_0.2Zn_0.8Fe_2−x Ce _x O₄ ferrite fibers possibly owing to the lattice distortion and internal-stress. Both the lattice constant and grain size increase slightly with the increase of the Ce³⁺ ion doping content. The soft magnetic properties of Mn-Zn ferrite fibers can be improved by a small amount of Ce³⁺ ion doping with an increase of the saturated magnetization and a decrease of the coercivity.     

Investigation on Oxygen Chemical Diffusion Properties of Perovskite Oxides (La1?x Pr x )0.6Sr0.4Co0.8Fe0.2O3?δ

Perovskite oxide samples of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (x = 0.2, 0.4, 0.6, 0.8) are obtained by solid-state reaction method. The oxygen chemical diffusion properties of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ are determined by electrical conductivity relaxation technique. The results show that the conductivity of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ increases with the increase of oxygen partial pressure. The (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ samples have a high oxygen chemical diffusion coefficient, which decreases linearly with a decrease in temperature and an increase in Pr content. The oxygen chemical diffusion coefficient D _chem remains fairly constant at high PO₂. The oxygen chemical diffusion coefficient is the highest for (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ with x = 0.2, and attains a value of 9.41 × 10⁻⁵ cm² s⁻¹ at 600 °C. This shows the material’s promise as a cathode material for intermediate temperature solid oxide fuel cells.     

Polarization study on doped lanthanum gallate electrolyte using impedance spectroscopy

Alternating current complex impedance spectroscopy studies were conducted on symmetrical cells of the type [gas, electrode/La_1−x Sr _x Ga_1−y Mg _y O₃ (LSGM) electrolyte/electrode, gas]. The electrode materials were slurry-coated on both sides of the LSGM electrolyte support. The electrodes selected for this investigation are candidate materials for solid oxide fuel cell (SOFC) electrodes. Cathode materials include La_1−x Sr _x MnO₃ (LSM), La_1−x Sr _x Co _y Fe_1−y O₃ (LSCF), a two-phase particulate composite consisting of LSM and doped-lanthanum gallate (LSGM), and LSCF + LSGM. Pt metal electrodes were also used for the purpose of comparison. Anode material investigated was the Ni + Ce_0.85Gd_0.15O₂ composite. The study revealed important details pertaining to the charge-transfer reactions that occur in such electrodes. The information obtained can be used to design electrodes for intermediate temperature SOFCs based on LSGM electrolytes. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Effects of dopant content on optical and electrical properties of In<Subscript>2</Subscript>O<Subscript>3</Subscript>: W transparent conductive films

The In2O3:W (IWO) films with different W content were deposited on glass substrate using direct current sputtering method. The structure, surface morphology, and optical and electrical properties were investigated. Results showed that both the carrier concentration and carrier mobility were increased with the doping of W. The IWO film with the lowest resistivity of 1. 0× 10-3 Ω· cm, highest carrier mobility of 43. 7 cm2. W-1. s-1 and carrier concentration of 1. 4× 1020 cm-3 was obtained at the content of 2. 8 wt. ％. The average optical transmittance from 300 nm to 900 nm reached 87. 6％.     

Influence of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the properties of KBT-NBT-BT lead-free piezoelectric ceramics

0.144(K0.5Bi0.5)TiO3-0.85(Na0.5Bi0.5)TiO3-0.006BaTiO3(KBT-NBT-BT) lead-free piezoelectric ceramics were prepared using a conventional solid state method.The influence of Sb2O3 doping on the crystal phase,surface microstructure and properties of the KBT-NBT-BT lead-free piezoelectric ceramics were investigated using X-ray diffraction(XRD),scanning electron microscope(SEM) and other analytical methods.The results show that all compositions are of pure perovskite structure solid states.Sb2O3 doping does not influence the microstructure of KBT-NBT-BT lead-free piezoelectric ceramics obviously in the Sb2O3 doping range of 0.1-0.5 wt.%.Sb2O3 functions as a donor when doped small amount,while functions as a acceptor when doped large amount.The piezoelectric strain constant(d33) increases first and then decreases;the dielectric constant(ε3T3/ε0) and the dielectric loss(tanδ) decrease continuously when the amount of Sb2O3 dopant increases.When the doping amount of Sb2O3 is 0.1 wt.%,the KBT-NBT-BT piezoelectric ceramics with good comprehensive properties are obtained,whose d33,ε3T3/ε0 and tanδ are 147 pC/N,1510 and 4.2%,respectively.     

Effect of Dy doping on magnetism of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>CoO<Subscript>3</Subscript> system

The effect of Dy doping on magnetism of La0. 7Sr0. 3CoO3 system was studied through the measurements of M-T curves and M-H curves. The results show that with Dy content increasing, Tc decreases, M weakens, the coercive force strengthens, and the samples exhibit the abnormal phenomenon that M increases continuously with T decreasing in low temperature range. Research indicates that the variation of magnetism in the system comes from the changes of lattice parameters and magnetic environment caused by Dy doping and from the spin-state transition of Co ions induced by Dy ions.     

Structural, magnetic and electrical transport properties for a series of La1−xSrxFe1−xMnxO3 (0.3 ≤ x ≤ 0.7) compounds

The structural, electrical transport and magnetic properties have been studied for compounds: La_1−xSr_xFe_1−xMn_xO₃ (0.3 ≤ x ≤ 0.7). The lattice parameter, a, first decreases with x, and followed by an increase when Sr²⁺ and Mn⁴⁺ was continuously doped. The cell parameters, b and c, slightly decrease with coupled substitution of Sr²⁺ for La³⁺ and Mn⁴⁺ for Fe³⁺. In the paramagnetic temperature range, formation of magnetic clusters is suggested; the sizes of clusters decrease with x up to 0.5, following that they increase sharply with continuing doping. The electrical behaviors of all specimens demonstrate insulators and the electrical resistivity increases with content of Mn⁴⁺ and Sr²⁺ ions doped. A variable range hopping model is suitable to describe electrical transport process for the compounds at low temperature. At high temperature the electrical transport process can be described by bipolaron model for all compounds.