Fabrication and properties of Ba(Zr1−xCex)0.9Y0.1O2.95/NaCl composite electrolyte materials

Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95/NaCl (x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10⁻² S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen.     

Electrical, magnetic, and Hall properties of AlxCoCrFeNi high-entropy alloys

This investigation explores the electrical and magnetic properties of as-cast, -homogenized, and -deformed Al_xCoCrFeNi (C-x, H-x, and D-x, respectively) alloys at various temperatures from 4.2 to 300 K. Experimental results reveal that carrier density of the alloys is of 10^22-23 cm⁻³. H-x has a carrier mobility of 0.40-2.61 cm² V⁻¹ s⁻¹. The residual electrical resistivity of the alloys varies from 100 to 220 μΩ cm. The temperature coefficient of resistivity (TCR) of H-2.00 is small (82.5 ppm/K). Therefore, defects in the lattice dominate electrical transportation. Some compositions exhibit Kondo-like behavior. At 300 K, H-0.50, H-1.25, and H-2.00 are ferromagnetic, while H-0.00, H-0.25, and H-0.75 are paramagnetic. Al and AlNi-rich phases reduce the ferromagnetism of single FCC and single BCC H-x, respectively. Spin glass behavior of some compositions is also observed. Alloys H-x are of the hole-like carrier type, and ferromagnetic H-x exhibits an anomalous Hall effect (AHE).     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

Hydrothermal synthesis of superconductors Ba1−xKxBiO3 and double perovskites Ba1−xKxBi1−yNayO3

Superconductors Ba_1−xK_xBiO₃ and body-centered double perovskites Ba_1−xK_xBi_1−yNa_yO₃ have been selectively synthesized by a facile hydrothermal route. The appropriate ratio and adding sequence of initial reagents, alkalinity, reaction temperature and time are the critical factors that influence the crystal growth of the compounds. The purity and homogeneity of the crystals were detected by the ICP, SEM, EDX and TEM studies. Magnetic measurements show that the superconducting transition temperatures T_C of Ba_1−xK_xBiO₃ decrease from 22 K (for x = 0.35) to 8 K (for x = 0.55) with increasing the K doping level.     

Nanocrystalline Fe1−xCoxSn2 solid solutions prepared by reduction of salts in tetraethylene glycol

In an effort to improve the electrochemical performance of tin intermetallic phases as electrode active material for lithium-ion batteries, Fe_1−xCo_xSn₂ solid solutions with x = 0.0, 0.25, 0.3, 0.5, 0.6 and 0.8 were prepared by chemical reduction in tetraethylene glycol. Precise control of the synthesis conditions allowed single-phase nanocrystalline materials to be prepared, with particle diameters of about 20 nm and cubic, nanorods, and U-shaped morphologies. The substitution of iron by cobalt induced a contraction of the unit cell volume. The hyperfine parameters of the ⁵⁷Fe Mössbauer spectra were sensitive to the Co/Fe substitution and revealed a superparamagnetic behaviour. In lithium cells nanocrystalline Fe_1−xCo_xSn₂ active materials delivered reversible capacities above 500 mAh g⁻¹ that depended on the composition and cycling conditions. The intermediate compositions exhibit better electrochemical performance than the end compositions CoSn₂ and FeSn₂.     

Thermoelectric properties of Cu1−xPtxFeO2 (0.0 ≤ x ≤ 0.05) delafossite-type transition oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite were synthesized by solid state reaction method for studying thermoelectric properties. The properties of Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the high temperature ranging from 300 to 960 K. The results of Seebeck coefficient, electrical conductivity and power factor were increased with increasing Pt substitution and temperature. The thermal conductivity was decreased from 5.8 to 3.5 W/mK with increasing the temperature from 300 to 960 K. An important results, the highest value of power factor and ZT is 2.0 × 10⁻⁴ W/mK² and 0.05, respectively, for x = 0.05 at 960 K.     

Synthesis, thermal stability and properties of [(Fe1−xCox)72Mo4B24]94Dy6 bulk metallic glasses

A series of [(Fe_1−xCo_x)₇₂Mo₄B₂₄]₉₄Dy₆ (x = 0.1, 0.2, 0.3, 0.4 and 0.5 at.%) bulk metallic glasses (BMGs) in rod geometries with critical diameter up to 3 mm were fabricated by copper mold casting method. This alloy system exhibited good thermal stability with high glass transition temperature (T_g) 860 K and crystallization temperature (T_x) 945 K. The addition of Co was found to be effective in adjusting the alloy composition deeper to eutectic, leading to lower liquidus temperature (T_l). The [(Fe_0.8Co_0.2)₇₂Mo₄B₂₄]₉₄Dy₆ alloy showed the largest supercooled liquid region (ΔT_x = T_x − T_g = 92 K), reduced glass transition temperature (T_rg = T_g/T_l = 0.622) and gamma parameter (γ = T_x/(T_g + T_l) = 0.424) among the present system. Maximum compressive fracture strength of 3540 MPa and micro-Vickers hardness of 1185 kg/mm² was achieved, resulting from the strong bonding structure among the alloy constituents. The alloy system possessed soft magnetic properties with high saturation magnetization of 56.61-61.78 A m²/kg and coercivity in the range of 222-264.2 A/m, which might be suitable for application in power electronics devices.     

The studies of phase relation, microstructure, magnetic transition, magnetocaloric effect in (Gd1−xErx)5Si1.7Ge2.3 compounds

The phase relation, microstructure, Curie temperatures (T_C), magnetic transition, and magnetocaloric effect of (Gd_1−xEr_x)₅Si_1.7Ge_2.3 (x = 0, 0.05, 0.1, 0.15, and 0.2) compounds prepared by arc-melting and then annealing at 1523 K (3 h) using purity Gd (99.9 wt.%) are investigated. The results of XRD patterns and SEM show that the main phases in those samples are mono-clinic Gd₅Si₂Ge₂ type structure. With increase of Er content from x = 0 to 0.2, the values of magnetic transition temperatures (T_C) decrease linearly from 228.7 K to 135.3 K. But the (Gd_1−xEr_x)₅Si_1.7Ge_2.3 compounds display large magnetic entropy near their transition temperatures in a magnetic field of 0-2 T. The maximum magnetic entropy change in (Gd_1−xEr_x)₅Si_1.7Ge_2.3 compounds are 24.56, 14.56, 16.84, 14.20, and 13.22 J/kg K⁻¹ with x = 0, 0.05, 0.1, 0.15, and 0.2, respectively.     

Thermoelectric properties of Bi2SexTe3−x prepared by Bridgman method

Bi₂Se_xTe_3−x crystals with various x values were grown by Bridgman method. The electrical conductivity, σ, was found to decrease with increasing Se content. The highest σ of 1.6 × 10⁵ S m⁻¹ at room temperature was reached at x = 0.12 with a growth rate of 0.8 mm h⁻¹. The Seebeck coefficient, S, was less dependent on Se content, all with positive values showing p-type characteristics, and the highest S was measured to be 240 μV K⁻¹ at x = 0.24. The lowest thermal conductivity, κ, was 0.7 W m⁻¹ K⁻¹ at x = 0.36. The electronic part of κ, κ_el, showed a decrease with increasing Se content, which implies that the hole concentration as the main carriers was reduced by the addition of Se. The highest dimensionless figure of merit, ZT, at room temperature was 1.2 at x = 0.36, which is attributed to the combination of a rather high electrical conductivity and Seebeck coefficient and low thermal conductivity.     

Structural characterization of layered LiNi0.85−xMnxCo0.15O2 with x = 0, 0.1, 0.2 and 0.4 oxide electrodes for Li batteries

We report the synthesis of LiNi_0.85−xCo_0.15Mn_xO₂ positive electrode materials from Ni_0.85−xCo_0.15Mn_x(OH)₂ and Li₂CO₃. XRD and XPS are used to study the effect of Mn-doping on the microstructures and oxidation states of the LiNi_0.85−xCo_0.15Mn_xO₂ materials. The analysis shows that Mn-doping promotes the formation of a single phase. With increasing substitution of Mn ions for Ni ions, the lattice parameter a decreases, while the lattice parameters c and c/a increase. XPS revealed that the oxidation states of Ni, Co and Mn in LiNi_0.85−xCo_0.15Mn_xO₂ compounds (where x = 0.1, 0.2 and 0.4) were +2/+3, +3 and +4. The substitution of Mn ions for Ni ions induces a decrease in the average oxidation state of Ni. Because the substitution of Mn for Ni ions is complex, the extent of the changes between the lattice parameter and L_M-O differ. The occupation of Ni in Li sites is affected by the ordering of Mn⁴⁺ with Ni²⁺ and Mn⁴⁺ with Li⁺.     

Effects of Tl-filling into the voids and Rh substitution for Co on the thermoelectric properties of CoSb3

In order to enhance the thermoelectric (TE) properties of CoSb₃, we tried to reduce the lattice thermal conductivity (κ_lat) by filling Tl into the voids and substitution of Rh for Co. We prepared polycrystalline samples of Tl_x(Co_1−yRh_y)₄Sb₁₂ (x = 0, 0.05, 0.10, 0.15, 0.20 and y = 0.1, 0.2) and examined their TE properties from room temperature to 750 K. All the samples indicated negative values of the Seebeck coefficient (S). Both the electrical resistivity and the absolute values of the S decreased with increasing the Tl-filling ratio. The Tl-filling and Rh substitution reduced the κ_lat, due to the rattling and the alloy scattering effects. The minimum value of the κ_lat was 1.54 W m⁻¹ K⁻¹ at 550 K obtained for Tl_0.20(Co_0.8Rh_0.2)₄Sb₁₂. Tl_0.20(Co_0.8Rh_0.2)₄Sb₁₂ exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.58 at around 600 K.     

Synthesis and thermoelectric properties of the PbSe1−xTex alloys

The PbSe_1−xTe_x alloys with x = 0.2, 0.3, 0.5, 0.85 and 1.0 were prepared by induction melting, ball milling and spark plasma sintering techniques. The thermoelectric properties of the samples were investigated. The XRD analysis indicated that all samples are NaCl-type structure solid solutions Pb(Se,Te) containing nanograins. Increasing Te content resulted in increasing the lattice parameter a. The thermoelectric measurements show that all samples are n-type semiconductors in temperature range from 300 K to 673 K. The electrical resistivity of the doped sample is much smaller than that of pure PbSe, but comparable to that of PbTe. The absolute Seebeck coefficients for the doped sample PbSe_1−xTe_x with x = 0.2, 0.3 and 0.5 range from 150 μV/K at 300 K to 250 μV/K at 673 K, which is much larger than that of pure PbSe (66-138 μV/K), but smaller than that of PbTe (230-310 μV/K) in the same experimental conditions. The thermal conductivity for the doped sample PbSe_1−xTe_x with x = 0.2, 0.3 and 0.5 range from 0.95 to 0.66 W/m K, which is much smaller than that of pure PbSe (2.1-1.3 W/m K) or PbTe (1.4-1.1 W/m K). As a result, the figure of merit for the doped sample can be enhanced. The maximum dimensionless figure of merit ZT of 1.15 was obtained in the sample PbTe_0.5Se_0.5 at 573 K, more than 50% higher than that of pure PbTe prepared in the same condition.     

High temperature thermoelectric properties and energy transfer devices of Ca3Co4−xAgxO9 and Ca1−ySmyMnO3

The high temperature oxide thermoelectric materials of p-type Ca₃Co_4−xAg_xO₉ (denoted as p-Co349/Ag_x) and n-type Ca_1−ySm_yMnO₃ (denoted as n-Mn113/Sm_y) were prepared by the self-ignition method combined with a sintering technique. The influence of doping Ag and Sm on the thermoelectric properties of the corresponding materials was evaluated. The figures of merit, ZT, for the p-Co349/Ag_0.2 and n-Mn113/Sm_0.02 materials reached maxima of 0.20 and 0.15 at 973 K, respectively. The performances of thermoelectric devices constructed with the p- and n-type pairs were evaluated in terms of the maximum output power (P_max) and manufacturing factor. The P_max and volume power density for the four-leg devices reached 36.8 mW and 81.9 mW cm⁻³ at ΔT of 523 K, respectively.     

Microwave dielectric properties of temperature stable Li2ZnxCo1−xTi3O8 ceramics

The Li₂Zn_xCo_1−xTi₃O₈ (x = 0.2-0.8) solid solution system has been synthesized by the conventional solid-state ceramic route and the effect of Zn substitution for Co on microwave dielectric properties of Li₂CoTi₃O₈ ceramics has also been investigated. The microwave dielectric properties of these ceramics show a linear variation between the end members for all compositions. The optimized sintering temperatures of Li₂Zn_xCo_1−xTi₃O₈ ceramics increase with increasing content of Zn. The specimen with x = 0.4 sintered at 1050 °C/2 h exhibits an excellent combination of microwave dielectric properties with ?_r = 27.7, Q_u × f = 57,100 GHz and τ_f = −1.0 ppm/°C.     

Synthesis and characterization of MWCNTs/Co1−xZnxFe2O4 magnetic nanocomposites and their use in hydrogels

A novel magnetic nanocomposite of multiwalled carbon nanotubes (MWCNTs) decorated with Co_1−xZn_xFe₂O₄ nanocrystals was synthesized successfully by an effective solvothermal method. The as-prepared MWCNTs/Co_1−xZn_xFe₂O₄ magnetic nanocomposite was used for the functionalization of P/H hydrogels as a prototype of device to show the potential application of the nanocomposites. The nanocomposites were characterized by X-ray diffraction analysis, transmission electron microscopy and vibrating sample magnetometer. The results show that the saturation magnetization of the MWCNTs/Co_1−xZn_xFe₂O₄ magnetic nanocomposites increases with x when the Zn²⁺ content is less than 0.5, but decreases rapidly when the Zn²⁺ content is more than 0.5. The saturation magnetization as a function of Zn²⁺ substitution reaches a maximum value of 57.5 emu g⁻¹ for x = 0.5. The probable synthesis mechanism of these nanocomposites was described based on the experimental results.     

High-temperature thermoelectric properties of late rare earth-doped Ca3Co4O9+δ

Misfit-layered oxides Ca_3−xLn_xCo₄O_9+δ with Ln = Dy, Er, Ho, and Lu were synthesized using solid state reactions. The resulting samples were hot-pressed (HP) at 1123 K in air for 2 h under a uniaxial pressure of 60 MPa. Thermoelectric properties of Ca_3−xLn_xCo₄O_9+δ were investigated up to 1200 K. Both the Seebeck coefficient and electrical resistivity increase upon Ln substitution for Ca. Among the Ln-doped samples, the magnitude of Seebeck coefficient tends to increase with decreasing ionic radius of Ln³⁺. The Ln-doped samples exhibit a lower thermal conductivity than the non-doped one due to a decrease of their lattice thermal conductivity. The dimensionless figure of merit, ZT, reaches 0.36 at 1073 K for the Ca_2.8Lu_0.2Co₄O_9+δ sample, which is about 1.6 times larger than that for the non-doped counterpart.     

Preparation and characterization of La1−xKxFeO3 (x = 0-1) by self-propagating high-temperature synthesis for use as soot combustion catalyst

This paper proposes La_1−xK_xFeO₃ prepared by self-propagating high-temperature synthesis (SHS) as an alternative to platinum catalysts for promoting diesel soot combustion. The catalytic property of eleven products SHSed with different substitution ratios of potassium (x = 0-1) was experimentally evaluated using a thermobalance. In the mass loss curves of the product, T₅₀ was defined as the temperature at which the weight of the reference soot decreases to half its initial weight. The BET specific surface area of SHSed La_1−xK_xFeO₃ depended on x strongly. All the products showed good oxidation catalytic activity. Despite having the smallest surface area (0.11 m²/g) among the obtained products, La_0.9K_0.1FeO₃ (x = 0.1) was found to be the best catalyst with the lowest T₅₀ (442 °C). T₅₀ of La_1−xK_xFeO₃ decreased with increasing x for x > 0.2. The products with x = 0.6 and 0.8 were the second-best catalysts in terms of their T₅₀. Moreover, average apparent activation energy of La_0.9K_0.1FeO₃ (x = 0.1) calculated by Friedman method using TG was as much as 61 kJ/mol lower than that of Pt/Al₂O₃ catalyst. In conclusion, potassium-substituted SHSed La_1−xK_xFeO₃ can be used as an alternative to Pt/Al₂O₃ for soot combustion.     

Fabrication and properties of p-type K doped Zn1−xMgxO thin film

A series of K doped Zn_1−xMg_xO thin films have been prepared by pulsed laser deposition (PLD). Hall-effect measurements indicate that the films exhibit stable p-type behavior with duration of at least six months. The band gap of the K doped Zn_1−xMg_xO films undergoes a blueshift due to the Mg incorporation. However, photoluminescence (PL) results reveal that the crystallinity decreased with the increasing of Mg content. The fabricated K doped p-type Zn_0.95Mg_0.05O thin film exhibits good electrical properties, with resistivity of 15.21 Ω cm and hole concentration of 5.54 × 10¹⁸ cm⁻³. Furthermore, a simple ZnO-based p-n heterojunction was prepared by deposition of a K-doped p-type Zn_0.95Mg_0.05O layer on Ga-doped n-type ZnO thin film with low resistivity. The p-n diode heterostructure exhibits typical rectification behavior of p-n junctions.     

Structural, optical and electromagnetic properties of Bi1−xHoxFeO3 multiferroic materials

Bi_1−xHo_xFeO₃ (x = 0.00, 0.05, 0.10, 0.15 and 0.20) polycrystalline ceramics were synthesized by a solid-state reaction and their structural, absorption, Raman scattering, impedance and magnetic properties were investigated. The substitution of rare earth Ho for Bi was found to decrease the impurity phase in BiFeO₃ ceramics. There appears an anomalous change in the lattice constants, optical band gap as well as the impedance spectroscopy and magnetization of samples at x = 0.10, suggesting a limit of dissolubility of Ho doped ions in BiFeO₃. Additionally, the Raman measurement performed for the lattice dynamics study of Bi_1−xHo_xFeO₃ samples reveals a band centered at around 1000-1300 cm⁻¹ which is associated with the resonant enhancement of two-phonon Raman scattering in the multiferroic Bi_1−xHo_xFeO₃ samples. Ho-doped BiFeO₃ also showed a ferromagnetic-like behavior with M_r = 1070 × 10⁻⁴ and M_s = 1.60 emu/g for optimum content x = 0.10, which is similar to the solid solution system of BiFeO₃.     

Effect of Ag-doping on crystal structure and high temperature thermoelectric properties of c-axis oriented Ca3Co4O9 thin films by pulsed laser deposition

Ag-doped Ca₃Co₄O₉ thin films with nominal composition of Ca_3−xAg_xCo₄O₉ (x = 0∼0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x ≤ 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca₃Co₄O₉ thin films could reach 0.73 mW m⁻¹ K⁻² at around 700 K, which was about 16% higher than that of the pure Ca₃Co₄O₉ thin film.