Electrical properties of binder-free thick film BaYxBi1−xO3 NTC thermistors

The microstructure and electrical properties of BaY_xBi_1−xO₃ thick film negative temperature coefficient thermistors, fabricated by screen printing, were investigated. The sintered thick films were the single-phase solid solutions of the BaY_xBi_1−xO₃ compounds with a monoclinic structure. The added Y₂O₃ led to a significant decrease in the grain size of the thermistors. The resistivity and coefficient of temperature sensitivity for the BaY_xBi_1−xO₃ (0 ≤ x ≤ 0.15) thick film NTC thermistors decreased first with increasing x in the range of x < 0.04 and then increased with further increase in x.     

Resistivity, thermopower, and thermal conductivity of nickel doped compounds Cr1−xNixSb2 at low temperatures

Substitutional compounds Cr_1−xNi_xSb₂ (0 ≤ x ≤ 0.1) were synthesized, and the effect of Ni substitution on transport and thermoelectric properties of Cr_1−xNi_xSb₂ were investigated at the temperatures from 7 to 310 K. The results indicated that the magnitudes of the resistivity and thermopower of Cr_1−xNi_xSb₂ decreased greatly with increasing Ni content at low temperatures, owing to an increase in electron concentration caused by Ni substitution for Cr. Experiments also showed that the low-temperature lattice thermal conductivity of Cr_1−xNi_xSb₂ decreased substantially with increasing Ni content due to an enhancement of phonon scattering by the increased number of Ni atoms. As a result, the figure of merit, ZT, of lightly doped Cr_0.99Ni_0.01Sb₂ was improved at T > ∼230 K. Specifically, the ZT of Cr_0.99Ni_0.01Sb₂ at 310 K was approximately ∼29% larger than that of CrSb₂, indicating that thermoelectric properties of CrSb₂ can be improved by an appropriate substitution of Ni for Cr.     

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.     

Luminescence studies of Ba1−xMg2−y(PO4)2:xEu, yMn phosphor

The phosphors BaMg₂(PO₄)₂ doped with Eu²⁺ and Mn²⁺ solely or doubly were prepared by solid state reaction, and their luminescent properties were also investigated. Under the excitation of 322 nm, it has been observed a broad blue emission band centered at 417 nm and a red emission band centered at about 665 nm, resulting from Eu²⁺ and Mn²⁺, respectively. Resonance-type energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly overlapping the emission spectra of Eu²⁺ and the excitation spectra of Mn²⁺. According to the changes of relative intensities of Eu²⁺ and Mn²⁺ emission, efficiencies of energy transfer were calculated. Based on the principle of energy transfer, the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺.     

Effect of the impurity LixNi1−xO on the electrochemical properties of 5 V cathode material LiNi0.5Mn1.5O4

The formation of impurity Li_xNi_1−xO when synthesizing spinel LiNi_0.5Mn_1.5O₄ using solid state reaction method, and its influence on the electrochemical properties of product LiNi_0.5Mn_1.5O₄ were studied. The secondary phase Li_xNi_1−xO emerges at high temperature due to oxygen deficiency for LiNi_0.5Mn_1.5O₄ and partial reduction of Mn⁴⁺ to Mn³⁺ in LiNi_0.5Mn_1.5O₄. Annealing process can diminish oxygen deficiency and inhibit impurity Li_xNi_1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi_0.5Mn_1.5O₄ that contains Li_xNi_1−xO can deliver about 120 mAh g⁻¹.     

Relationships between Zr substitution for Ti and microwave dielectric properties in Mg(ZrxTi1−x)O3 ceramics

The influence of Zr substitution for Ti on the microwave dielectric properties and microstructures of the Mg(Zr_xTi_1−x)O₃(MZ_xT) (0.01 ≤ x ≤ 0.3) ceramics was investigated. The quality factors of Mg(Zr_xTi_1−x)O₃ ceramics with x = 0.01-0.05 were improved because the solid solution of a small amount of Zr⁴⁺ substitution in the B-site could increase density and grain size. An excess of Zr⁴⁺ resulted in the formation of a great deal of secondary phase that declined the microwave dielectric properties of MZ_xT ceramics. The temperature coefficient of resonant frequency (τ_f) of Mg(Zr_xTi_1−x)O₃ ceramics slightly increased with increasing Zr content, and the variation in τ_f was attributed to the formation of secondary phases.     

Structural, elastic and electronic properties of Mg(Cu1−xZnx)2 alloys calculated by first-principles

The structural, elastic and electronic properties of Mg(Cu_1−xZn_x)₂ alloys (x = 0, 0.25, 0.5,and 0.75) were investigated by means of first-principle calculations within the framework of density functional theory (DFT). The calculation results demonstrated that the partial substitution of Cu with Zn in MgCu₂ leaded to an increase of lattice constants, and the optimized structural parameters were in very good agreement with the available experimental values. From energetic point of view, it was found that with increase of Zn content the structural stability of Mg(Cu_1−xZn_x)₂ alloys decreased apparently. The single-crystal elastic constants were obtained by computing total energy as a function of strain, and then the bulk modulus B, shear modulus G, Young's modulus Y and Poisson's ratio ν of polycrystalline aggregates were derived. The calculated results showed that among the Mg(Cu_1−xZn_x)₂ alloys, MgCuZn exhibited the largest stiffness, while Mg₂Cu₃Zn showed the best ductility. Finally, the electronic density of states (DOSs) and charge density distribution were further studied and discussed.     

CuIn1−xAlxS2 thin films prepared by sulfurization of metallic precursors

CuIn_1−xAl_xS₂ thin films (x = 0, 0.09, 0.27, 0.46, 0.64, 0.82 and 1) with thicknesses of approximately 1 μm were formed by the sulfurization of DC sputtered Cu-In-Al precursors. All samples were sulfurized in a graphite container for 90 min at 650 °C in a 150 kPa Ar + S atmosphere. Final films were studied via X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-Raman spectroscopy. It was found that all samples were polycrystalline in nature and their lattice parameters varied slightly nonlinearly from {a = 5.49 Å, c = 11.02 Å} for CuInS₂ to {a = 5.30 Å, c = 10.36 Å} for CuAlS₂. No unwanted phases such as Cu_2−xS or others were observed. Raman were recorded at a room temperature and the most intensive and dominant A₁ phonon frequency varied nonlinearly from 294 cm⁻¹ (CuInS₂) to 314 cm⁻¹ (CuAlS₂).     

Structural, morphological and optical properties of Bi2−xSbxSe3 thin films grown by electrodeposition

Ternary single-phase Bi_2−xSb_xSe₃ alloy thin films were synthesized onto Au(1 1 1) substrates from an aqueous solution containing Bi(NO₃)₃, SbCl₃, and SeO₂ at room temperature for the first time via the electrodeposition technique. The electrodeposition of the thin films was studied using cyclic voltammetry, compositional, structural, optical measurements and surface morphology. It was found that the thin films with different stoichiometry can be obtained by controlling the electrolyte composition. The as-deposited films were crystallized in the preferential orientation along the (0 1 5) plane. The SEM investigations show that the film growth proceeds via nucleation, growth of film layer and formation of spherical particles on the film layer. The particle size and shape of Bi_2−xSb_xSe₃ films could be changed by tuning the electrolyte composition. The optical absorption spectra suggest that the band gap of this alloy varied from 0.24 to 0.38 eV with increasing Sb content from x = 0 to x = 0.2.     

Effect of non-magnetic doping on multi-step magnetization behavior of Dy50−xAlxAg50

The electrical transport and magnetization measurements have been carried out on Al-doped polycrystalline intermetallic compounds Dy_50−xAl_xAg₅₀ (x = 0, 0.3, 0.6, 1.2, 1.8) in a pulsed high magnetic field, in which multi-step magnetization is observed. Partial substitute of non-magnetic Al³⁺ for Dy³⁺ ions in the compounds increases the critical magnetic fields and the relative area of the magnetic hysteresis loop, which result from the pinning effect, lattice distortion, the change of coupling strength and dilution effect related to the Al³⁺ doping.The experimental results indicate that non-magnetic Al³⁺ ions and induced amorphous phase can pin the rotation and/or growth of magnetic domains, thus, the critical magnetic field can be enhanced by doping non-magnetic ions in the magnetic materials, especially in the permanent magnet materials.     

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.     

Combustion synthesis of Ti3Si1−xAlxC2 solid solutions from TiC-, SiC-, and Al4C3-containing powder compacts

Preparation of the Ti₃Si_1−xAl_xC₂ solid solution with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS) using TiC-, SiC-, and Al₄C₃-containing powder compacts. Due to the variation of reaction exothermicity with sample stoichiometry, the combustion temperature and reaction front velocity decreased with increasing Al content of Ti₃Si_1−xAl_xC₂ for the TiC- and Al₄C₃-added samples, but increased for the samples with SiC. In contrast to the formation of Ti₃(Si,Al)C₂ as the dominant phase for the TiC- and SiC-added samples, TiC was identified as the major constituent in the final products of samples adopting Al₄C₃. In addition, the evolution of Ti₃(Si,Al)C₂ was improved by increasing the Al content of the TiC- and SiC-added powder compacts, but deteriorated considerably upon the increase of Al₄C₃ in the Al₄C₃-containing sample.     

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.     

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.     

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⁺.     

Bismuth-containing semiconductors: Linear and nonlinear optical susceptibilities of GaAs1−xBix alloys

Using all electron full potential - linearized augmented plane wave (FP-LAPW) method the linear and nonlinear optical susceptibilities of cubic GaAs_1−xBi_x alloys with x varying between 0.25 and 0.75 with increment of 0.25 are investigated. We have applied the generalized gradient approximation (GGA) for the exchange and correlation potential. In addition the Engel-Vosko generalized gradient approximation (EVGGA) was used. The reflectivity, refractivity, absorption coefficient and the loss function of these ternary alloys were investigated. The absorption coefficient shows that GaAs_0.25Bi_0.75 possess the highest coefficient among the investigated alloys which supports our previous observation that the band gap decreases substantially with increasing Bi content and the materials with very small energy band gap possess the highest absorption coefficient. The investigation of the linear and nonlinear optical susceptibilities of GaAs_1−xBi_x shows a strong band gap reduction as commonly found experimentally.     

Mechanical and phonon properties of the superhard LuB2, LuB4, and LuB12 compounds

We have studied structural, elastic, and lattice dynamical properties of the LuB_2, LuB_4, and LuB₁₂ compounds by using the plane-wave pseudopotential approach to the density-functional theory within the generalized gradient approximation. We have considered three different crystal structures of LuB_x: LuB₂ (P6/mmm), LuB₄ (P4/mbm), and LuB₁₂ (Fm-3m). The most stable structure is found to be tetragonal (P4/mbm) structure. The comparative results on the basic physical parameters such as lattice constants, bulk modulus, bond distances, elastic constants, shear modulus, Young's modulus, and Poison's ratio are reported. Also, we have predicted that LuB₄ and LuB₁₂ compounds are potential superhard materials. Furthermore, the phonon dispersion curves and corresponding phonon density of states (DOS) are computed for considered phases. Our structural and some other results are in agreement with the available experimental and other theoretical data.     

Influence of partial substitution of Ge on crystallization kinetics, microstructure and magnetic property of Fe44Co44−xZr7B5Gex alloys

Partial substitution of Ge for Co in Fe₄₄Co₄₄Zr₇B₅ amorphous alloy is found to have a large influence on crystallization kinetics and magnetic property of the alloy. Activation energy of nanocrystallization of FeCo phase (primary crystallization) decreases by 90 kJ/mol with 4 at.% Ge substitution, while that of precipitations of Zr-type phase from a residual amorphous phase (secondary crystallization) increases by 106 kJ/mol. The suppression of the secondary crystallizations stabilizes the FeCo nanocrystals embedded in the residual amorphous phase for the Fe₄₄Co_44−xZr₇B₅Ge_x until higher temperatures. It is proposed that the stabilization mechanism is attributed to preferential partitioning of Ge in the residual amorphous phase revealed by scanning transmission electron microscopy analysis. Microstructure and coercivity for the annealed alloys are also presented in combination with the effect of the Ge substitutions.     

Magnetomechanical properties of epoxy-bonded Sm1−xNdxFe1.55 (0 ≤ x ≤ 0.56) pseudo-1-3 magnetostrictive particulate composites

Pseudo-1-3 magnetostrictive particulate composites consisting of light rare earth (Sm and Nd)-based magnetostrictive Sm_1−xNd_xFe_1.55 particles with the Nd content x of 0-0.56 and randomly distributed sizes of 10-180 μm embedded and aligned in a passive epoxy matrix are fabricated using the particulate volume fraction of 0.5. The quasistatic magnetomechanical properties of the composites are investigated and the results are compared with their monolithic alloys for various x. The composites exhibit similar qualitative trends in properties with the alloys for all x. The Sm_0.92Nd_0.08Fe_1.55 composite shows a large unsaturated magnetostriction λ of −530 ppm at 500 kA/m and a high piezomagnetic coefficient d₃₃ of −2.0 nm/A at 100 kA/m as a result of the magnetocrystalline anisotropy compensation between Sm³⁺ and Nd³⁺ ions in the Sm_0.92Nd_0.08Fe_1.55 alloy.     

Preparation, structure and electrical conductivity of the pyrochlore-type phase Sm2Zr2O7 codoped with bivalent magnesium and trivalent dysprosium cations

The pyrochlore-type phases with the compositions of SmDy_1−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.20) have been prepared by pressureless-sintering method for the first time as possible solid electrolytes. The structure and electrical conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics have been studied by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy measurements. SmDy_1−xMg_xZr₂O_7−x/2 (x = 0, 0.05, 0.10) ceramics exhibit a single phase of pyrochlore-type structure, and SmDy_1−xMg_xZr₂O_7−x/2 (x = 0.15, 0.20) ceramics consist of pyrochlore phase and a small amount of the second phase magnesia. The total conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics obeys the Arrhenius relation, and the total conductivity of each composition increases with increasing temperature from 673 to 1173 K. SmDy_1−xMg_xZr₂O_7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest total conductivity value is about 8 × 10⁻³ S cm⁻¹ at 1173 K for SmDy_1−xMg_xZr₂O_7−x/2 ceramics.