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.     

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.     

Investigation on temperature dependence of photoluminescence in Sr1.7Eu0.3MxCeO4.15+x/2 (M = Li, Na, K, x = 0, 0.3) red phosphors

The temperature-dependent luminescence of Sr_1.7Eu_0.3M_xCeO_4.15+x/2 (M = Li⁺, Na⁺, K⁺, x = 0, 0.3) samples was investigated and discussed in the temperature range from 303 to 573 K. It is found that the thermal quenching temperature of samples decreases with Li⁺-/Na⁺-doping but increases with the incorporation of K⁺. We suggest that these observations are resulted from two factors. One is that the incorporation of Li⁺/Na⁺/K⁺ ions reduces the strength of potential field at the O²⁻ sites, and then results in a red-shift of the Eu-O charge transfer band. The other is that Δr expands with Li⁺-/Na⁺-doping but shrinks with K⁺-doping. We consider that it is a feasible way to adjust the temperature-dependent luminescence properties of materials by introducing appropriate impurities.     

Photoluminescent properties of LiSrxBa1−xPO4:RE (RE = Sm, Eu) f-f transition phosphors

Rare-earth ions (Sm³⁺ or Eu³⁺) doped LiSr_xBa_1−xPO₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) f-f transition phosphor powders were prepared by a high temperature solid-state reaction. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the phase structure of the sample changes from LiBaPO₄ to LiSrPO₄ when x changes from 0 to 1.0. The excitation spectra indicate that only direct excitation of rare earth ions (Sm³⁺ or Eu³⁺) can be observed. The doped rare earth ions show their characteristic emission in LiSr_xBa_1−xPO₄, i.e., Eu³⁺⁵D₀-⁷F_J (J = 0, 1, 2, 3, 4), Sm³⁺⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2), respectively. The dependence of the emission intensities of the LiSr_xBa_1−xPO₄:Sm³⁺ and LiSr_xBa_1−xPO₄:Eu³⁺ phosphors on the x value and Ln³⁺ (Ln³⁺ = Sm³⁺, Eu³⁺) concentration is also investigated.     

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.     

Synthesis and electrochemical performance of Li(Ni0.8Co0.15Al0.05)0.8(Ni0.5Mn0.5)0.2O2 with core-shell structure as cathode material for Li-ion batteries

The core-shell structure cathode material Li(Ni_0.8Co_0.15Al_0.05)_0.8(Ni_0.5Mn_0.5)_0.2O₂ (LNCANMO) was synthesized via a co-precipitation method. Its applicability as a cathode material for lithium ion batteries was investigated. The core-shell particle consists of LiNi_0.8Co_0.15Al_0.05O₂ (LNCAO) as the core and a LiNi_0.5Mn_0.5O₂ as the shell. The thickness of the LiNi_0.5Mn_0.5O₂ layer is approximately 1.25 μm, as estimated by field emission scanning electron microscopy (FE-SEM). The cycling behavior between 2.8 and 4.3 V at a current rate of 18 mA g⁻¹ shows a reversible capacity of about 195 mAh g⁻¹ with little capacity loss after 50 cycles. High-rate capability testing shows that even at a rate of 5 C, a stable capacity of approximately 127 mAh g⁻¹ is retained. In contrast, the capacity of LNCAO rapidly decreases in cyclic and high rate tests. The observed higher current rate capability and cycle stability of LNCANMO can be attributed to the lower impedance including charge transfer resistance and surface film resistance. Differential scanning calorimetry (DSC) indicates that LNCANMO had a much improved oxygen evolution onset temperature of approximately 251 °C, and a much lower level of exothermic-heat release compared to LNCAO. The improved thermal stability of the LNCANMO can be ascribed to the thermally stable outer shell of LiNi_0.5Mn_0.5O₂, which suppresses oxygen release from the host lattice and not directly come into contact with the electrolyte solution. In particular, LNCANMO is shown to exhibit improved electrochemical performance and is a safe material for use as an electrode for lithium ion batteries.     

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.     

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⁺.     

Luminescence and energy transfer of Mn and Tb in Y3Al5O12 phosphors

Mn²⁺ is an excellent luminescent ion with variable color from green, yellow to red in different hosts and has been widely utilized in recent years. The luminescent intensity of Mn²⁺ in many hosts is so low that the correlative application is restricted. In the present paper, two methods, i.e. employing a charge compensator and introducing a sensitizer, were adopted to enhance the luminescence of Mn²⁺ in Y₃Al₅O₁₂ (YAG). By employing Si⁴⁺ as a charge compensator, the doping content of Mn²⁺ (x) in Y₃Mn_xAl_5−2xSi_xO₁₂ can be lifted up to 0.4. Mn²⁺ in YAG emits orange light in a broad band. The peak wavelength shifts from 586 to 593 nm with the increasing x. The luminescent intensity of Mn²⁺ reaches its maximum when x = 0.1. Co-doping Tb³⁺ into Mn²⁺ doped YAG, the sensitization effect of Tb³⁺ on Mn²⁺ was observed clearly. The resonance energy transfer from Tb³⁺ to Mn²⁺ occurs because there is a well overlapping between emission spectrum of Tb³⁺ and excitation spectrum of Mn²⁺. A reasonable explanation for the sensitization effect of Tb³⁺ on the luminescence of Mn²⁺ was brought forward.     

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.     

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.     

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.     

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.     

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.     

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.     

An investigation on hydrogen storage kinetics of nanocrystalline and amorphous Mg2Ni1−xCox (x = 0-0.4) alloy prepared by melt spinning

In order to improve the hydrogen storage kinetics of the Mg₂Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg₂Ni_1−xCo_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and spun alloys are characterized by XRD, SEM and TEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-spun alloys is tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves are plotted by an electrochemical workstation. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg₂Ni-type alloy. Furthermore, the substitution of Co for Ni, instead of changing major phase Mg₂Ni, leads to forming secondary phases MgCo₂ and Mg. Both the melt spinning treatment and Co substitution significantly improve the hydrogen absorption and desorption kinetics. The high rate discharge ability, the hydrogen diffusion coefficient and the limiting current density of the alloys significantly increase with raising both the spinning rate and the amount of Co substitution.     

Preparation and electrical properties of perovskite ceramics in the system BaBi1−xSbxO3 (0 ≤ x ≤ 0.5)

The effect of the composition on the electrical properties of BaBi_1−xSb_xO₃ (0 ≤ x ≤ 0.5) negative temperature coefficient (NTC) thermistors was studied. Major phases present in the sintered bodies of BaBi_1−xSb_xO₃ (0 < x < 0.5) ceramics were BaBi_0.5Sb_0.5O₃ compounds with a rhombohedral structure and BaBiO₃ compounds with a monoclinal structure. Most pores were located in the grains of BaBiO₃ and BaBi_0.5Sb_0.5O₃ ceramics. It was apparent that the ρ₂₅ and B_25/85 constant of the thermistors increased with increasing Sb content.     

First principles study of structural, electronic and magnetic properties of Mg1−xMnxTe alloys

Density functional FP-LAPW + lo calculations have been performed to study the structural, electronic and magnetic properties of Mg_1−xMn_xTe for compositional parameter x = 0.25, 0.50, 0.75 and 1. Our calculations reveal the occurrence of ferromagnetism in these compounds in which the transition-metal atom is ordered in a periodical way thereby interacting directly with the host atoms. Results extracted from electronic band structure and density of states (DOS) of these alloys show the existence of direct energy band gap for both majority- and minority-spin cases, while the total energy calculations confirm the stability of ferromagnetic state as compared to anti-ferromagnetic state. The total magnetic moment for Mg_1−xMn_xTe for each composition is found to be approximately 5 μ_B, which indicates that the addition of Mn content does not affect the hole carrier concentration of the perfect MgTe compound. Moreover, the s-d exchange constant (N₀α) and p-d exchange constant (N₀β) are also calculated which are in accordance with a typical magneto-optical experiment. The estimated spin-exchange splitting energies originated by Mn 3d states energies, i.e. Δ_X(s-d) and Δ_X(p-d), show that the effective potential for minority-spin is more attractive than that of the majority-spin. Also, the p-d hybridization is found to cause the reduction of local magnetic moment of Mn and produce small local magnetic moments on the nonmagnetic Mg and Te sites.     

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.     

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).