Hole distribution in La2−xSrxCu1−yZn(Ni)yO4 (x ⩽ 1/8)

Simulation with interacting-potentials has been performed to investigate hole distribution in La_2−xSr_xCu_1−yZn(Ni)_yO₄ (y = 1/32 and x ⩽ 1/8). It is found that the orderly distributed hole configurations are more energetically favorable than the randomly distributed hole configurations. Moreover, the doped Zn²⁺ and Ni²⁺ ions can both act as stabilizing centers to localize the holes in their vicinity leading to an atomic-scale inhomogeneous distribution of holes. This atomic-scale inhomogeneities of holes obtained from our simulation is similar to that predicted by the “Swiss Cheese” model.     

Graphene-GaAs-graphene stacked layers for the improvement of the transmission at the wavelength of 1.55 μm

Transmission filter operating at the wavelength of 1.55 μm and based on stacked graphene-GaAs-graphene layers separated by air gaps is presented. By using the transfer matrix method (TMM), we show that the addition of a graphene layer at each interface of a GaAs-based stratified structure, which initially exhibit only 30% transmission at 1.55 μm, allows the active control of the transmission by the adjustment of the graphene chemical potential. Transmission of almost 100% at the wavelength of 1.55 μm is achieved after addition of graphene layers. These results show the potential role of stacked graphene-GaAs-graphene layers in the development of new optical active communications devices.     

Crystal structure and thermal expansion of LaCr1−xMgxO3, 0 < x ≤ 0.25

Solid solution LaCr_1?xMg_xO₃, 0 < х ≤ 0.25 was prepared by heating stoichiometric amounts of appropriate oxides in air at 1400 °C, 48 h. At room temperature it crystallizes in orthorhombically distorted GdFeO₃-type structure (a ≈ √2 × a_per; b ≈ √2 × a_pe; c ≈ 2 × a_per, where a_per – perovskite subcell parameter). High-temperature X-ray powder diffraction (HT XRPD) and dilatometry revealed first order phase transition to rhombohedral perovskite phase (R-3c, a ≈ √2 × a_per, c ≈ 2√3 × a_per) at 260–311 °C (OR phase transition). Crystal structures of room-temperature orthorhombic and high-temperature rhombohedral phases for LaCr_0.75Mg_0.25O₃ were refined using HT XRPD data. Temperature of OR phase transition increases gradually with increasing of magnesium content. Low-temperature orthorhombic phase exhibits TEC lower in comparison with high-temperature rhombohedral one (e.g. for LaCr_0.85Mg_0.15O₃ TEC(O) = 8.8 ppm K^?1; TEC(R) = 11.6 ppm K^?1). TEC for rhombohedral phase increases with increasing magnesium content from 10.4 ppm K^?1 for LaCr_0.95Mg_0.05O₃ to 12.1 ppm K^?1 for LaCr_0.75Mg_0.25O₃.     

Thermoelectric properties of Re6GaxSeyTe15−y (0 ≤ x ≤ 2; 0 ≤ y ≤ 7.5)

Thermoelectric properties of Re₆Ga_xSe_yTe_15?y (0 ≤ x ≤ 2; 0 ≤ y ≤ 7.5) were studied in the temperature range 90–320 K. The measurements revealed p-type semi-conductivity in all samples. Relatively high values of the Seebeck coefficients, α, were obtained in all samples. The electrical resistivities and room temperature Seebeck coefficients increased as selenium concentrations increased, for each value of x. The room temperature Seebeck coefficients and resistivities decreased as gallium content increased, for each value of y. Low carrier concentrations were found at room temperatures, in agreement with large Seebeck coefficient values. Measurements suggested hopping conduction between 150 K and 280 K for all samples. Temperature dependences of the Seebeck coefficient below 150 K were accounted for by phonon drag effect. The power factors for the samples were calculated. Theoretical discussions of dependences of the measured quantities on temperature and composition are given. Usefulness of these materials as thermoelectrics is also discussed.     

Synthesis and characterization of flower-like CuIn1−xGaxS2 (x = 0.3) microspheres

We report the formation and characterization of the flower-like CuIn_1?xGa_xS₂ (x = 0.3) microspheres using CuCl₂·2H₂O, GaCl₃, InCl₃ and l-cystine in the mixed solvent of ethylene glycol and distilled water (1:2, v/v) at 200 °C for 24 h. XRD results indicated that the CuIn_0.7Ga_0.3S₂ nanostructures have a (1 1 2) preferred orientation. The EDS and XPS analyses of the sample revealed that Cu, In, Ga and S were present in an atomic ratio of approximately 1:0.7:0.3:2. FESEM and TEM images showed that the product was microspheres, consisting of nanoplates with the thickness of about 20 nm. The optical properties were investigated by ultraviolet–visible (UV–vis) absorption spectroscopy and Raman spectroscopy. UV–vis absorption spectrum indicated that the band gap of as-synthesized flower-like CuIn_0.7Ga_0.3S₂ microspheres was about 2.427 eV. Raman spectrum of the obtained CuIn_0.7Ga_0.3S₂ exhibited a high-intensity peak at 302 cm^?1 could be assigned as A1-mode.     

Structural and electrical properties of high-quality 0.41 μm-thick InSb films grown on GaAs (1 0 0) substrate with InxAl1−xSb continuously graded buffer

High-quality InSb was grown on a GaAs (1 0 0) substrate with an InAlSb continuously graded buffer (CGB). The temperatures of In, Al K-cells and substrate were modified during the growth of InAlSb CGB. The cross-section TEM image reveals that the defects due to lattice-mismatch disappear near lateral structures in CGB. The measured electron mobility of 0.41 μm-thick InSb was 46,300 cm²/Vs at 300 K. These data surpass the electron mobility of state-of-the-art InSb grown by other methods with similar thickness of InSb.     

Atomic diffusion in the Fe [0 0 1] ∑ = 5 (3 1 0) and (2 1 0) symmetric tilt grain boundary

Both the formation and diffusion activation energies of single vacancy migrating intra-layer and inter-layer near the Fe [0 0 1] Σ = 5 (3 1 0) and (2 1 0) symmetric tilt grain boundaries have been calculated by using the MAEAM and a MD method. From energy minimization, the vacancy concentration in the second layer is higher than the one in the other layers for both (3 1 0) and (2 1 0) STGBs. By the diffusion activation energies of the vacancies migrating intra-layer and inter-layer, the vacancies located from the first to the eighth layers of (3 1 0) STGB as well as the ones located from the first to the tenth layers of (2 1 0) STGB are favorably migrated to the second layer. Thus there is a vacancy aggregation tendency to the second layer near the grain boundary. For the vacancy migrating intra-layer and inter-layer, the influences of the grain boundary are respectively as far as to the fifth and eighth layers for (3 1 0) STGB as well as to the sixth and tenth layers for (2 1 0) STGB.     

Reinvestigation of the tensile strength and fracture property of Ni(1 1 1)/α-Al2O3(0 0 0 1) interfaces by first-principle calculations

First-principle calculations are performed to reinvestigate the mechanical tensile property and failure characteristic of Ni/Al₂O₃ interfaces, in order to clear the inconsistence existed in the literatures. Four types of interface models without initial lateral stresses are used, i.e., Al-terminated O-site, O-terminated Al-site, Al-terminated Al-site and Al-terminated H-site models. Two kinds of tensile methods, viz., uniaxial extension and uniaxial tension, are adopted to check the mechanical responses of these interface models. It is found that the results under uniaxial extension are generally consistent with those under uniaxial tension, including the overall shapes of stress–strain curves and the values of tensile strengths. Moreover, the initial lateral stresses have an apparent influence on the mechanical properties of the interfaces during the loading process, such as tensile strength, fracture strain and the work of separation. Our simulation results also clarified that, under tensile loading, the most stable O-terminated Al-site interface model tends to fracture in a brittle way along the sublayer between in-plane Ni–Ni atomic bonds, while all of the Al-terminated interface models will fail in a ductile fracture manner with relatively lower stress levels, breaking along the interlayer between the Ni(1) and Al(1) layers.     

Synthesis and electrical conductivity of La0.6Sr0.4Ru1−xMgxO3−δ (x = 0–0.6) perovskite solid solution

Sr and Mg were doped at La- and Ru-sites of perovskite oxide LaRuO₃, respectively, to enhance electrical conductivity and catalytic property as a cathode material for a low temperature solid oxide fuel cell. Crystal structure and particle morphology of La_0.6Sr_0.4Ru_1?xMg_xO_3?δ powders (shorten as LSRM) and electrical conductivity of sintered LSRM were studied. LSRM powders (x = 0–0.6) were prepared by co-precipitation method using metal nitrate solutions and ammonium carbonate solution. The freeze-dried powders were heated at 1273 K in air to form LSRM solid solution of orthorhombic structure. The true densities and particle sizes of LSRM solid solution, where valence of Ru was estimated to be 3+, decreased with increasing Mg content. The electrical conductivity of LSRM at x = 0–0.3 was almost independent of temperature and was in a range of 19–360 S cm^?1 at 1073 K. Hole conduction contributed to the high electrical conductivities. LSRM at x = 0.4 and 0.5 was a mixed conductor of oxide ions and holes, and showed a conductivity of 11 S cm^?1 at 1073 K in air. This conductivity decreased at a lower oxygen pressure and reached a constant value below 10 Pa of oxygen pressure.     

Co1−xZnxFe2O4 (0 ≤ x ≤ 1) nanocrystalline solid solution prepared by the polyol method: Characterization and magnetic properties

Highly crystalline stoichiometric Co_1?xZn_xFe₂O₄ (0 ≤ x ≤ 1) nanoparticles were successfully synthesized by the polyol process. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy (TEM), infrared spectroscopy (IR), zero-field ⁵⁷Fe Mössbauer spectrometry and magnetic measurements using a SQUID magnetometer were employed to investigate the effect of the substitution of Zn²⁺ ions for Co²⁺ ones on the structure, and the magnetic properties of the cobalt ferrite, CoFe₂O₄. The unit cell parameter almost increases linearly with increasing Zn concentration, x, following Vegard's law. The red and blue shifts observed for the metal-oxygen ν₁ and ν₂ IR vibration bands, respectively, were consistent with the preferential entrance of Zn²⁺ ions in tetrahedral sites. Besides, detailed magnetic investigation in correlation with the cation distribution has been reported. All the particles exhibit superparamagnetic behaviour at room temperature. In addition, the magnetic characteristics (blocking temperature, saturation magnetization, coercivity, Curie temperature) clearly depend on the chemical composition and cation distribution. Both the blocking temperature and Curie temperature decrease drastically with Zn composition, x, increase. Further, the saturation magnetization follows an almost bulk-like behaviour with values notably larger than that of the bulk, mainly attributed to cation distribution deviation.     

Two-photon absorption of Tl1−xIn1−xSnxSe2 (x = 0, 0.1, 0.2, 0.25) single crystalline alloys and their nanocrystallites

Two-photon absorption (TPA) of Tl_1−xIn_1−xSn_xSe₂ (x = 0, 0.1, 0.2, 0.25) was studied at CO₂ laser wavelength 9.4 μm with pulse duration 1 μs. The studies were performed at different temperatures and for the nanocrystallite sizes varying within the 7–200 nm. The nanocrystals were fabricated by mechanical milling with simultaneous acoustical field treatment and porous filter size separation. The studies have shown that the TPA may be enhanced during the decrease of the nanocrystallite sizes below 50–60 nm. There exists also some critical x value at which the TPA value begin substantially to increase. The comparison with other chalcogenide crystals is performed. The studied nanocrystallites are relatively stable to the infrared laser treatment and are not hygroscopic which allow to use them in different IR optoelectronic devices.     

Thermo-optical properties of LaMg1 − xNixAl11O19 (0 ≤ x ≤ 1) hexaaluminates for metallic thermal protection system

LaMg_1 ? xNi_xAl₁₁O₁₉ (x = 0, 0.25, 0.5, 0.75, 1) ceramics are fabricated by pressureless-sintering method at 1700 °C for 10 h in air. The microstructure and thermo-optical properties of LaMg_1 ? xNi_xAl₁₁O₁₉ ceramics are investigated by the X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The influence of NiO doping on structure and thermo-optical properties of LaMg_1 ? xNi_xAl₁₁O₁₉ ceramics is investigated. The partial substitution of Ni²⁺ for Mg²⁺ results in a significant increase in emissivity at low wavelengths as compared with unmodified LaMgAl₁₁O₁₉. When the Ni²⁺ content increases to x = 0.75 or above, LaMg_1 ? xNi_xAl₁₁O₁₉ ceramics have a high emissivity value above 0.70 at low wavelengths at 500 °C. The measured emissivity of all LaMg_1 ? xNi_xAl₁₁O₁₉ ceramics shows a similar trend in the wavelength range of 6 to 14 μm.     

Structure,nonstoichiometry, sintering and oxygen permeability of perovskite SrCo1−2x(Fe,Nb)xO3−δ (x = 0.05, 0.10) oxides

The novel Fe/Nb co-substituted SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides have been synthesized and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG), and scanning electron microscopy (SEM). The XRD and DSC results demonstrate that the structural stability of the Fe/Nb co-substituted samples x = 0.05, 0.10 is improved greatly compared to the sample x = 0.00. The Fe/Nb co-doping in the SrCoO_3?δ oxide results in the improved structural stability of the SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides. The nonstoichiometric and sintering properties were investigated by TG and SEM, and the oxygen permeation fluxes were measured at 800–950 °C for the sample x = 0.10. The improved oxygen permeability of the ceramic SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.10) membrane compared to the (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3?δ and SrCo_0.8Fe_0.2O_3–δ membranes, was observed under an air/He oxygen partial pressure gradient at 800–950 °C.     

Microwave-assisted synthesis and characterization of Ti1 − xVxO2 (x = 0.0–0.10) nanopowders

Ti_1 ? xV_xO₂ (x = 0.0–0.10) nanopowders were successfully synthesized by a microwave-assisted sol–gel technique and their crystal structure and electronic structure were investigated. The products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV–Vis spectroscopy. The results revealed that TiO₂ powders maintained the anatase phase for calcination temperature below 600 °C, but gradually changed to the rutile phase above 800 °C. The formation of the rutile phase was completed at 1000 °C. For Ti_1 ? xV_xO₂ (x = 0.05) powders, the phase transformation appeared at 600 °C. The absorption edge of Ti_1 ? xV_xO₂ (x > 0) powders broadened to the visible region with increasing V concentration and a strong visible light absorption was obtained with 10% V doping. V doping and subsequent coexistence of both anatase and rutile phases in our Ti_1 ? xV_xO₂ nanoparticles are considered to be responsible for the enhanced absorption of visible light up to 800 nm.     

Electronic structure of Cu100−xZrx (x = 40, 50, 60) metallic glasses

The electronic structure of Cu_100−xZr_x (x = 40, 50, 60) metallic glasses was investigated by ultraviolet photoelectron spectroscopy and X-ray photoemission spectroscopy, the valence band spectra of these alloys were analyzed by a large shift of the Cu d-band peaks to higher binding energies upon increasing Cu content. Photoemission experiments and first-principles calculations prove that the values of density of states at Fermi level of Cu_100−xZr_x metallic glasses are mainly dominated by Zr rather than Cu. This work will enlighten further research on understanding the inheritance of metallic glasses and designing new metallic glasses with unique properties.     

XPS and Mössbauer studies on BaSn1−xNbxO3 (x ≤ 0.100)

A few compositions of perovskite oxide BaSn_1?xNb_xO₃ (with x ≤ 0.10) system, prepared by solid state ceramic method, have been studied employing XPS and Mössbauer spectroscopy techniques. Mössbauer spectra of these compositions in the temperature range of 78–300 K reveal that the oxidation state of Sn is +4. In XPS measurements, compositions with x ≤ 0.010 show no evidence of Nb⁵⁺ signal whereas the compositions with x ≥ 0.050 show clear evidence of Nb⁵⁺ signals indicating some unreacted Nb₂O₅ component in the system. This confirms the earlier report where presence of small amount of unreacted Nb₂O₅ was predicted.     

Electrical properties of nanostructures (CoFeZr)x + (Al2O3)1−x with use of alternating current

CoFeZr–Al₂O₃ nanocomposite films of 3–5 μm thickness, containing metallic alloy nanoparticles embedded into the dielectric alumina matrix, have been deposited on a glass ceramic substrate using magnetron sputtering of composite target in Ar gas ambient. Measurements of AC conductance and lagging have been performed within the frequency range of 50 Hz–1 MHz at the temperatures from 79 K to 373 K in the initial (as-deposited) samples as well as directly after their isochronous (15 min) annealings within the temperature range from 398 K to 648 K with 25 K step.The observed variations of real part AC electrical conductivity with temperature and frequency σ_real(T, f) in the as-deposited films display transition from dielectric to metallic behaviour when crossing the percolation threshold x_C in the studied nanocomposites. After annealing of the samples below the x_C the σ_real(T, f) progress follows the hopping law of electron conductivity with sigmoidal frequency dependence. The samples being far beyond the percolation threshold revealed transition from metallic to activational σ_real(T) law after high-temperature annealing attributed to the internal oxidation of metallic nanoparticle by excess of oxygen presented in the as-deposited samples.     

Magnetically separable Zn1-xCuxFe2O4 (0 ≤ x ≤ 0.5) nanocatalysts for the transesterification of waste cooking oil

Copper doped zinc ferrite Zn_1-xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized via sonication assisted microwave method. The prepared nanoparticles were characterized by XRD, FTIR, HR-SEM, EDX, DRS and VSM analysis. Average crystallite size were in range 5.84 nm to 8.55 nm. FTIR results reveal, bands at 420 cm⁻¹ (Zn²⁺O²⁻) and 547 cm⁻¹ (Fe³⁺O²⁻) confirming tetrahedral and octahedral positions of the spinel structure formation. All the samples showed ferromagnetic behavior at room temperature. The Zn_0.5Cu_0.5Fe₂O₄ sample showed high saturation magnetization (M_s = 74.09 emu/g) and high magnetic moment (3.0 μ_B). The prepared magnetic nano spinels were subsequently employed to evaluate the catalytic activity for biodiesel production. The transesterification process followed pseudo first order rate kinetic model. An excellent catalytic activity for biodiesel production was acheived (98.9%) and the catalyst was recoverable quickly using an external magnet.