Synthesis and characterization of LiCo0.3−xGaxNi0.7O2 (x = 0, 0.05) as a cathode material for lithium ion battery

The single phase of LiCo_0.3−xGa_xNi_0.7O₂ (x = 0, 0.05) was synthesized by a sol–gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The powders are homogeneous and have a good-layered structure. The synthesized LiCo_0.25Ga_0.05Ni_0.7O₂ exhibits better electrochemical performance with an initial discharge capacity of 180.0 mAh g⁻¹ and a capacity retention of 95.2% after 50 cycles between 2.8 and 4.4 V at 0.2C rate. The study on the structural evolution of the material during the cycling shows that Ga-doping improves the structure stability of LiCo_0.3Ni_0.7O₂ at ambient temperature and 55 °C. Meanwhile, Ga-doping not only suppresses the alternating current (AC) impedance of LiCo_0.3Ni_0.7O₂ but also promotes the Li⁺ diffusion in LiCo_0.3Ni_0.7O₂. Furthermore, thermal stability of the charged LiCo_0.25Ga_0.05Ni_0.7O₂ is improved, which may be attributed to the retard of O₂ evolution in LiCo_0.3Ni_0.7O₂ and the suppression of electrolyte oxidation during cycling by Ga-doping_.     

Doping-induced microstructural, textural and optical properties of In2Ti1−xVxO5+δ semiconductors and their role in the photocatalytic splitting of water

The physicochemical properties of V-doped indium titanates (In₂Ti_1−xV_xO_5+δ, 0.0 ≤ x ≤ 0.2) were investigated by using XPS, powder XRD, UV–vis, SEM and luminescence spectroscopy techniques. The Rietveld refinement of XRD data revealed that even though the V-containing samples were isostructural with In₂TiO₅ (orthorhombic space group Pnma), a systematic x-dependent variation was noticeable in the Ti–O bond lengths in [TiO₆] octahedral units, cell parameters and in the value of δ. XPS results confirmed the coexistence of V⁵⁺ and V⁴⁺ states, leading thereby to an enhancement in oxygen non-stoichiometry in the doped samples. A loading-dependent progressive shift from 400 to 750 nm was also observed in the onset of the absorption edge, indicating a significant narrowing of the band gap. Furthermore, the samples with higher V-content were comprised of the grain clusters having larger size and an irregular shape. The UV–vis, photoluminescence and thermoluminescence studies indicate that the doping-induced lattice defects may give rise to certain closely spaced acceptor/donor energy levels in between the band gap of host matrix. The indium titanates are found to serve as stable photocatalysts for water splitting under visible light, where oxygen was the major reaction product. The role of microstructural and morphological properties in the photocatalytic activity is discussed.     

Thermal expansion properties of Ln2−xCrxMo3O12 (Ln = Er and Y)

Structures and thermal expansion properties of Ln_2−xCr_xMo₃O₁₂ (Ln = Er and Y) have been investigated by X-ray powder diffraction. Rietveld analysis results of Ln_2−xCr_xMo₃O₁₂ indicate that compounds Er_2−xCr_xMo₃O₁₂ (0 ≤ x ≤ 0.3) and Y_2−xCr_xMo₃O₁₂ (0 ≤ x ≤ 0.2) crystallize in orthorhombic structure and exhibit negative thermal expansion, while both monoclinic and orthorhombic compounds Er_2−xCr_xMo₃O₁₂ (1.7 ≤ x ≤ 2.0) and Y_2−xCr_xMo₃O₁₂ (1.8 ≤ x ≤ 2.0) possess positive coefficient of thermal expansion. The coefficients of linear thermal expansion of orthorhombic Ln_2−xCr_xMo₃O₁₂ change from negative to positive with increasing chromium content. Thermogravimetric and differential scanning calorimetry have been used to study the hygroscopicity and the phase transition temperature.     

Microstructures and thermoelectric properties of p-type pseudo-binary AgxBi0.5Sb1.5−xTe3 (x = 0.05–0.4) alloys prepared by cold pressing

The p-type pseudo-binary Ag_xBi_0.5Sb_1.5−xTe₃ (x = 0.05–0.4) alloys were prepared by cold pressing. The thermal conductivities (κ) were calculated from the values of heat capacities, densities and thermal diffusivities measured, and range approximately from 0.66 to 0.56 (W K^− 1 m^− 1) for the Ag_xBi_0.5Sb_1.5−xTe₃ alloy with molar fraction x being 0.4. Combining with the electrical properties obtained in the previous study, the maximum dimensionless figure of merit ZT of 1.1 was obtained at the temperature of 558 K.     

Electrochemical characteristics of Ba0.5Sr0.5Co0.8Fe0.2O3−δ–Sm0.2Ce0.8O1.9 composite materials for low-temperature solid oxide fuel cell cathodes

In this paper, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ–xSm_0.2Ce_0.8O_1.9 (BSCF–xSDC, x = 0–60 wt.%) composite cathodes were prepared by soft chemical methods, and then examined for potential applications in lower temperature solid oxide fuel cells. Both DC polarization and AC impedance spectroscopy measurements indicated that the addition of SDC electrolyte into BSCF remarkably improved the electrochemical properties. The optimum composition was found to be BSCF–30SDC, which exhibited 5.5 times higher polarization current density and 15.1% polarization resistance, compared with the pure-phase BSCF cathode at 550 °C.     

Effect of Ca Substitution on the Superconductivity of La2.5Y0.5CaBa3(Cu0.88Fe0.12)7Oz

The structural and superconducting properties of single-phase La_2.5–y Y_0.5Ca_1+y Ba₃ (Cu_0.88Fe_0.12)₇O _z (LYCaBCuFe) (y= 0.0–1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T _c ^R=0 shows a marginal increase from 31 K to 37 K for y = 0.0–0.21 and thereafter it decreases with increasing y leading to zero T _c ^R=0 at y 0.84. This shows that the suppression of T _c from 80 K to 31 K by Fe doping at x = 0.12 La_2.5Y_0.5CaBa₃(Cu_1–x Fe _x )₇O _z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.     

Synthesis of layered Li1.2+x[Ni0.25Mn0.75]0.8−xO2 materials (0 ≤ x ≤ 4/55) via a new simple microwave heating method and their electrochemical properties

Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) was prepared by a new simple microwave heating method and the effect of extra Li⁺ content on electrochemistry of Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) was firstly revealed. X-ray diffraction identified that they had layered α-NaFeO₂ structure (space group R-3m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li⁺ is possibly incorporated in structure of layered Li_1.2Ni_0.2Mn_0.6O₂ (x = 0), accompanying oxidization of Ni²⁺ to Ni³⁺ to form Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni³⁺ appeared and increased in content with increasing x value. Charge–discharge tests showed that Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) truly displayed different electrochemical properties (different initial charge–discharge plots, capacities and cycleability). Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) in this work delivered the highest discharge capacity of 219 mAh g⁻¹ between 4.8 and 2.0 V. Increasing Li content (x value in Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂) reduced charge–discharge capacities, but significantly enhancing cycleability.     

Synthesis and electrochemical properties of Nb-doped Li3V2(PO4)3/C cathode materials for lithium-ion batteries

Li₃V_2−xNb_x(PO₄)₃/C cathode materials were synthesized by a sol-gel method. X-ray diffraction patterns demonstrated that the appropriate addition of Nb did not destroy the lattice structure of Li₃V₂(PO₄)₃, and enlarged the unit cell volume, which could provide more space for lithium intercalation/de-intercalation. Transmission electron microscopy and energy dispersive X-ray spectroscopy analysis illustrated that Nb could not only be doped into the crystal lattice, but also form an amorphous (Nb, C, V, P and O) layer around the particles. As the cathode materials of Li-ion batteries, Li₃V_2−xNb_x(PO₄)₃/C (x ≤ 0.15) exhibited higher discharge capacity and better cycle stability than the pure one. At a discharge rate of 0.5C, the initial discharge capacity of Li₃V_1.85Nb_0.15(PO₄)₃/C was 162.4 mAh/g. The low charge-transfer resistances and large lithium ion diffusion coefficients confirmed that Li₃V_2−xNb_x(PO₄)₃/C samples possessed better electronic conductivity and lithium ion mobility. These improved electrochemical performances can be attributed to the appropriate amount of Nb doping in Li₃V₂(PO₄)₃ system by enhancing structural stability and electrical conductivity.     

Superconductivity and Ferromagnetism of the Ru-1232 Compounds in the (Ru1?xNbx)Sr2(GdCe1.8Sr0.2)Cu2Oz System

The Ru-1232 compounds have been synthesized in the (Ru_1–xNb _x )Sr₂(GdCe_1.8Sr_0.2)Cu₂O _z system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T _c ^l and T _c ^h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T _c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T _m is about 90 K. This study also shows that both of the values of T _c and T _m become low with increasing x from 0.0 to 0.3.     

High-temperature oxygen non-stoichiometry, conductivity and structure in strontium-rich nickelates La2−xSrxNiO4−δ (x = 1 and 1.4)

Oxygen non-stoichiometry, electrical conductivity and thermal expansion of La_2−xSr_xNiO_4−δ phases with high levels of strontium-substitution (1 ≤ x ≤ 1.4) have been investigated in air and oxygen atmosphere in the temperature range 20–1050 °C. These phases retain the K₂NiF₄-type structure of La₂NiO₄ (tetragonal, space group I4/mmm). The oxygen vacancy fraction was determined independently from thermogravimetric and neutron diffraction experiments, and is found to increase considerably on heating. The electrical resistivity, thermal expansion and cell parameters with temperature show peculiar variations with temperature, and differ notably from La₂NiO_4±δ in this respect. These variations are tentatively correlated with the evolution of nickel oxidation state, which crosses from a Ni³⁺/Ni⁴⁺ to a Ni²⁺/Ni³⁺ equilibrium on heating.     

Partial substitution of Li for Cu in superconducting YBa2Cu3Oy

0.33–33% of the Cu in superconducting YBa₂Cu₃O _y has been replaced by Li (i.e.,x=0.01–1 in single-phase or nominal YBa₂Cu_3–x Li_xO_y). X-ray diffraction powder patterns remain the same as for YBn₂Cu₃O _y , with identical patterns up to about 17% substitution (i.e.,x=0.5). At higher percentages an additional phase appears. Electrical conductivity measurements indicate a small elevation ofT _c at low Li content. Starting at about 5% Li (x=0.15),T _c declines progressively and its width increases asx is raised.     

Structural, electronic and optical properties of Sn1−xSbxO2

The goal of this paper is to undertake a detailed first principle calculation of the structural, electronic and optical properties of Sn_1−xSb_xO₂. The results show that the stability of Sn_1−xSb_xO₂ in the full range of Sb content points to the probability of a continuous solid solution, where the increasing Sb content leads to volume expansion with different variation trends in the lattice constants. The increase of Sb concentration in the semiconductor–metal–semimetal transition occurs in consonance with the corresponding changes in its structural, electronic and optical properties. Two competing mechanisms play essential roles in this transition, namely; the many body effect and the atom disorder. Our calculations concur with previous X-ray diffraction, sheet resistance, resistivity and optical parameters detections. The studies present a practical way of tailoring the physical behaviors of Sn_1−xSb_xO₂ through the alloying technique.     

Nanostripes in GdBa2Cu3Ox high-Tc superconductors

High-T_c superconductors with light rare earth (LRE) elements instead of Y exhibit nanoscale stripe structures on the surface as observed by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) scans. Within the GdBa₂Cu₃O_x (GdBCO) system exhibiting relatively high critical current densities, nanoclusters arranged in a stripe-like fashion are observed in undoped material, while adding of nanoparticles (ZnO₂, ZrO₂) leads to the formation of nanostripes as observed in other LRE superconductors. The nanostripes in doped GdBCO exhibit periodicties between 20 and 50 nm and corresponding step heights of 0.3–0.8 nm. Using polarized light microscopy and electron backscatter diffraction (EBSD) analysis, we determined the direction of the nanostripes with respect to the known twin structure.     

Influence of hole filling by Ti on the superconductivity of YBa2Cu3O7?δ

The structural and superconducting properties of YBa₂(CU_1–x Ti _x )₃O_z samples are investigated using X-ray diffraction, ac susceptibility, and oxygen content measurements. The effect of increasing Ti concentration in YBa₂(Cu_1–x Ti _x )₃O_z lowers the oxygen content and decreasesT _c, which is attributed to hole filling by Ti.     

Origin of Spin-Glass Behavior of Zn1 ? xMnxO

Alternating current susceptibility has been studied for polycrystalline Zn_{1 – x} Mn _x O. Stoichiometric samples demonstrate Curie–Weiss behavior, which indicates mostly antiferromagnetic interactions. Magnetic susceptibility can be described by a diluted Heisenberg magnet model developed for semimagnetic semiconductors. High-pressure oxygen annealing induces spin-glass like behavior in Zn_{1 – x} Mn _x O by precipitation of ZnMnO₃ in the paramagnetic matrix.     

The structural and electrical property of CuCr1 − xNixO2 delafossite compounds

A series of CuCr_1 − xNi_xO₂ (0 ≤ x ≤ 0.06) polycrystalline samples was prepared. The electrical conductivity was measured in the temperature range of 160–300 K. It was found that the electrical conductivity (σ) increases rapidly with the doping of Ni²⁺ ions. At room temperature, the σ is 0.047 S cm^− 1 for the sample with x = 0.06, which is two orders of magnitude larger than that of the CuCrO₂ sample (9.49E− 4 S cm^− 1). The Seebeck coefficients are positive for all samples, which indicate p-type conducting of the samples. The experimental results imply that it is possible to get higher electrical conductivity p-type transparent conducting oxides (TCO) from CuMO₂ by doping with divalent ions.     

Superconductivity at 103 K in CdBa2(Ca0.7Y0.3)Cu2Oy

A cadmium analogue of the mercury system with nominal composition CdBa₂(Ca_1–xY_x)Cu₂O_y has been synthesized. Thex=0 samples contain about 12 vol.% of the 1212 phase but are not superconducting. Thex=0.3 samples are superconducting atT _on = 103 K. The EDX analysis of 18 microcrystals shows a broad cationic distribution of the different components. The observed broad superconducting transition is attributed to the variousT _c of the different microcrystals.     

Luminescence properties of Sn2P2Se6 crystals

A large family of Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) semiconductor-ferroelectric crystals were obtained by the Bridgman technique. The photoluminescence properties of the Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) family crystals strongly depend on their chemical composition, excitation energy and temperature. The influence of the Pb → Sn and S → Se isovalent substitutions on the luminescence properties of a crystal with the Sn₂P₂Se₆ basic composition was investigated. A broad emission band observed in the Sn₂P₂Se₆ crystal with a maximum roughly at 600 nm (at T = 8.6 K) was assigned to a band-to-band electron-hole recombination, whereas broad emission bands, peaked near 785 nm (at T = 8.6 K) and 1025 nm (at T = 44 K) were assigned to an electron-hole recombination from defect levels localised within the bandgap. Possible types of recombination defect centres and specific mechanisms of luminescence in the Sn₂P₂Se₆ semiconductor-ferroelectric crystals were considered and discussed on the basis of the obtained results and the referenced data.     

Magnetization and Susceptibility Studies on BaZrO3-Doped YBa2Cu3O7 ? x Bulk Superconductors

We studied the YBa₂Cu₃O_{7 – x} bulk superconductor doped with BaZrO₃ up to 50 wt.%, obtained by solid-state reaction powder technology. From DC magnetization loops and low frequency AC susceptibility measurements we determined the influence of the BaZrO₃ doping level on the critical temperature, critical current density, field for full penetration, and intergrain lower critical field. The results show that even high content of BaZrO₃ does not lead to degradation of the superconducting properties of bulk YBa₂Cu₃O_{7 – x} .     

High-capacity superconducting current leads of Y1Ba2Cu3O7?x

We have fabricated and measured a high-capacity superconducting current lead composed of a Y₁Ba₂Cu₃O_7–x cylinder, 20 cm long and 0.9 cm² cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2×10^–7 V/cm (p = 8×10^–10 ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y₁Ba₂Cu₃O_7–x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.