Ferromagnetism in Zn1−xCrxTe (x = 0.05, 0.15) films grown on GaAs(1 0 0) substrate

Zn_1−xCr_xTe (x = 0.05, 0.15) films were grown on GaAs(1 0 0) substrate by thermal evaporation method. X-ray diffraction analysis showed the presence of ZnCrTe phase without any secondary phase. The surface was analyzed by high resolution magnetic force microscope and profile measurements showed orientation of magnetic domains in the range of 0.5–2 nm with increase of Cr content. Magnetic moment–magnetic field measurements showed a characteristic hysteresis loop even at room temperature. The Curie temperature was estimated to be greater than 300 K. From the electron spin resonance spectra, the valence state of Cr in ZnTe was found to be +2 with d² electronic configuration. Hall effect study was done at room temperature and the result showed the presence of p-type charge carriers and hole concentration was found to increase from 5.95 × 10¹² to 6.7 × 10¹² m⁻³ when Cr content increases. We deduce the origin of ferromagnetic behavior based on the observed experimental results.     

Thermal analysis of specific heat measurements in glassy Se80−xTe20Sbx alloys in glass transition region

In the present report, we have done specific heat measurements in glassy Se_80?xTe₂₀Sb_x (0 ≤ x ≤ 15) alloys in glass transition region. Differential scanning calorimetry (DSC) technique is used for this purpose. We have observed a tremendously huge increase in the specific heat (C_p) values at the glass transition temperature. The thermal analysis shows that the values of C_p below glass transition temperature and the difference of C_p values before and after glass transition (?C_p) are highly composition-dependent.     

Theoretical investigation of electronic structure and optical response in relation to the transport properties of Ga1−xInxN (x = 0, 0.25, 0.50, 0.75)

The state-of-the-art all-electron FLPAW method and the BoltzTrap software package based on semi-classical theory were adopted to explore the electronic structure and the optical and thermoelectric properties of Ga_1−xIn_xN. Ga_1−xIn_xN is predicted to be a direct band gap material for all values of x. Moreover, the band gap varies between 2.99 eV and 1.95 eV as x changes. Optical parameters such as the dielectric constant, absorption coefficient, reflectivity and refractive index are calculated and discussed in detail. The doping of In plays an important role in the modulation of the optical constants. The static dielectric constant ɛ(0) of Ga_1−xIn_xN was calculated as 3.95, 3.99, 3.99 and 4.03 at x = 0.00, 0.25, 0.50 and 0.75, respectively. The static refractive index is 2.0 for pure Ga_1−xIn_xN at x = 0.00. The thermal properties varied greatly as x fluctuated. The ternary alloy has large values for the Seebeck coefficient and figure of merit at high temperatures and is thus suitable for thermoelectric applications. Pure Ga_1−xIn_xN at x = 0 exhibited ZT = 0.80 at room temperature, and at higher temperatures, the thermal conductivity decreased with increased In doping.     

Intercomparison of Fluctuation Induced Conductivity of Cu0.5Tl0.5Ba2Can−1CunO2n+4−y (n = 2, 3, 4) superconductor thin films

An intercomparison of Fluctuation Induced Conductivity (FIC) of Cu_0.5Tl_0.5Ba₂Ca_n?1Cu_nO_2n+4?y (n = 2, 3, 4) [CuTl-12(n ? 1)n] superconductor thin films is given. We tried to find any correlation between the critical temperature and the parameters extracted from the excess conductivity data i.e. cross-over temperature, pseudogap temperature and fluctuation amplitudes. We found that the critical temperature seems to depend on the fluctuation amplitude; greater the fluctuation amplitude higher is the critical temperature.     

Raman scattering study of IrxRu1−xO2 mixed metal oxide nanowires (0 ≤ x ≤ 1)

Recent interests in mixed metal oxide nanostructured materials especially Ir_xRu_1−xO₂ compounds have been mainly driven by the technological application as electrocatalyst and electrode materials. We present room temperature Raman scattering results of single crystalline Ir_xRu_1−xO₂ (0 ≤ x ≤ 1) nanowires grown by atmospheric pressure chemical vapor deposition. We observed that the E_g, the A_1g, and the B_2g phonon modes of a single Ir_xRu_1−xO₂ nanowire are blue-shifted linearly with respect to the Ir contents from which we could get stoichiometry information. We also observed that the asymmetric lineshape and the broadening of the full width at half maximum of the E_g mode that involves the out-of-plane oxygen vibration. The unusual asymmetric broadening of the E_g phonon can be explained by the activation of the non-zone-center phonons due to substitutional disorder present in the system. We also found that there is a mixed mode of the A_1g and the B_2g phonons due to the substitutional disorder, in the range of 630–750 cm⁻¹.     

Impedance study of SrTi1−xFexO3−δ (x = 0.05 to 0.80) mixed ionic-electronic conducting model cathode

SrTi_1?xFe_xO_3?δ (STF) model cathodes, with compositions of x = 0.05 to 0.80 were deposited onto single crystal yttria stabilized zirconia by pulsed layer deposition as dense films with well defined area and thickness and studied by electrochemical impedance spectroscopy as a function of electrode geometry, temperature and pO₂. The STF cathode was observed to exhibit typical mixed ionic-electronic behavior with the electrode reaction occurring over the full electrode surface area rather than being limited to the triple phase boundary. The electrode impedance was observed to be independent of electrode thickness and to the introduction of CGO interlayers and inversely proportional to the square of the electrode diameter, pointing to surface exchange limited kinetics. Values for the surface exchange coefficient, k, were calculated and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors such as (La,Sr)(Co,Fe)O₃, thereby, confirming the suitability of STF as a model mixed conducting cathode material. The surface exchange coefficient, k, was also found to be insensitive to orders of magnitude change in both bulk electronic and ionic conductivities.     

Theoretical investigation of the inversion parameter in Co3 − sAlsO4 (s = 0–3) spinel structures

The structural, energetic, and thermodynamic properties of the Co_3 ? sAl_sO₄ (s = 0, 1, 2, and 3) crystal family are studied using periodic DFT calculations. We provide a quantitative discussion of the cation distribution effect on the cell parameter, the oxygen Wyckoff position, the interatomic distances and the energies of the structures. It is demonstrated that the low cobalt containing CoAl₂O₄ spinel is the most stable structure of the Co_3 ? sAl_sO₄ (s = 0, 1, 2, and 3) crystal family.     

Defect chemistry and oxygen transport of (La0.6Sr0.4 − xMx)0.99Co0.2Fe0.8O3 − δ, M = Ca (x = 0.05, 0.1), Ba (x = 0.1, 0.2), Sr: Part II: Oxygen transport

This paper is the second part of a two part series, where the effects of varying the A-site dopant on the defect chemistry and transport properties of the materials (La_0.6Sr_0.4 ? xM_x)_0.99Co_0.2Fe_0.8O_3 ? δ, M = Sr, Ca (x = 0.05, 0.1), Ba (x = 0.1, 0.2) (LSMFC) have been investigated. In part I, the findings on the defect chemistry were reported, while the oxygen transport properties are reported here in part II. In the investigated material series, the amount of divalent dopant has been kept constant, while Sr ions have been substituted with Ca ions (smaller ionic radius) or Ba ions (larger ionic radius). The size difference induces different strains into the crystal structure in each composition. The possibility of simple relationships between various crystal strain parameters and the transport properties were analyzed. Oxygen pump controlled permeation experiments and a surface sensitive electrolyte probe were used to extract the permeability and surface resistance, r_s. The highest permeability was found for (La_0.6Sr_0.3Ca_0.1)_0.99Co_0.2Fe_0.8O_3 ? δ. The apparent activation energy of the permeability was 78 kJ/mol. The inverse surface resistance, r_s^? 1, also had an activated behavior with an activation energy close to 180 kJ/mol for most of the materials. A reversible transition to an abnormally low r_s was found in (La_0.6Sr_0.3Ca_0.1)_0.99Co_0.2Fe_0.8O_3 ? δ at T > 1223 K.     

Structural and electrochemical properties of LiNi0.5Mn0.5 − xAlxO2 (x = 0, 0.02, 0.05, 0.08, and 0.1) cathode materials for lithium-ion batteries

Layered LiNi_0.5Mn_0.5 ? xAl_xO₂ (x = 0, 0.02, 0.05, 0.08, and 0.1) series cathode materials for lithium-ion batteries were synthesized by a combination technique of co-precipitation and solid-state reaction, and the structural, morphological, and electrochemical properties were examined by XRD, FT-IR, XPS, SEM, CV, EIS, and charge–discharge tests. It is proven that the aliovalent substitution of Al for Mn promoted the formation of LiNi_0.5Mn_0.5 ? xAl_xO₂ structures and induced an increase in the average oxidation number of Ni, thereby leading to the shrinkage of the lattice volume. Among the LiNi_0.5Mn_0.5 ? xAl_xO₂ materials, the material with x = 0.05 shows the best cyclability and rate ability, with discharge capacities of 219, 169, 155, and 129 mAh g^? 1 at 10, 100, 200, and 400 mA g^? 1 current density respectively. Cycled under 40 mA g^? 1 in 2.8–4.6 V, LiNi_{0. 5}Mn_0.45Al_0.05O₂ shows the highest discharge capacity of about 199 mAh g^? 1 for the first cycle, and 179 mAh g^? 1 after 40 cycles, with a capacity retention of 90%. EIS analyses of the electrode materials at pristine state and state after first charge to 4.6 V indicate that the observed higher current rate capability of LiNi_{0. 5}Mn_0.45Al_0.05O₂ can be understood due to the better charge transfer kinetics.     

Hyperfine fields and magnetic anisotropy in Fe1000−x Gd x thin films and Fe80−x GdxB20(0≤x≤24) thin films and ribbons

The Mössbauer measurements performed on Fe_100–x Gd _x thin films and on Fe_80–x Gd _x B₂₀ both as thin films and ribbons show a dependence of the spins orientation and H_hyp versus temperature, Gd content and preparation conditions. Increasing the Gd content, the initial low anisotropy disappears and H_hyp decreases. A sharp increase of the anisotopy with temperature in ribbons with low Gd concentration is evidenced.     

Preparation,surface state and band structure studies of SrTi(1 − x)Fe(x)O(3 − δ) (x = 0–1) perovskite-type nano structure by X-ray and ultraviolet photoelectron spectroscopy

In this report, SrTi_(1 ? x)Fe_(x)O_(3 ? δ) photocatalyst powder was synthesized by a high temperature solid state reaction method. The morphology, crystalline structures of obtained samples, was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM), respectively. The electronic properties and local structure of the perovskite STF_x (0 ≤ x ≤ 1) systems have been probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. The effects of iron doping level x (x = 0–1) on the crystal structure and chemical state of the STF_x have been investigated by X-ray photoelectron spectroscopy and the valence band edges for electronic band gaps were obtained for STF_x by ultraviolet photoelectron spectroscopy (UPS). A single cubic perovskite phase of STF_x oxide was successfully obtained at 1200 °C for 24 h by the solid state reaction method. The XPS results showed that the iron present in the STF_x perovskite structure is composed of a mixture of Fe³⁺ and Fe⁴⁺ (SrTi_(1 ? x)[Fe³⁺, Fe⁴⁺]_(x)O_(3 ? δ)). When the content x of iron doping was increased, the amount of Fe³⁺ and Fe⁴⁺ increased significantly and the oxygen lattice decreased on the surface of STF_x oxide. The UPS data has confirmed that with more substitution of iron, the position of the valence band decreased.     

Growth and scintillation properties of (Lu1 − x Tmx)2SiO5 [x = 0.001, 0.01, 0.1, 1]

(Lu_1 − xTm_x)₂SiO₅ (x = 0.001, 0.01, 0.1, 1) single crystalline scintillators were grown by the μ-PD method. In transmittance measurement, absorption bands due to Tm³⁺ 4f–4f transitions were observed at 260, 292, 356, 463, 680 and 790 nm and they could be ascribed to the transition from the ³H₆ ground state to its excited states, ¹I₆, ³P₆,¹D₂, ¹G₄, ³F₃ and ³H₄, respectively. Strong emission peak due to ¹D₂ → ³F₄ transition of Tm³⁺ was shown at 453 nm under X-ray irradiation. Photoluminescence decay time constant caused by this transition were evaluated to be 11.9 μs. Tm 1% doped one exhibited the highest light yield of 3530 ± 200 photons/MeV when excited by ¹³⁷Cs gamma-ray exposure.     

Optical band gap and refractive index dispersion parameters of As x Se70Te30−x (0≤x≤30 at.%) amorphous films

Amorphous As _x Se₇₀Te_30?x thin films with (0≤x≤30 at.%) were deposited onto glass substrates by using thermal evaporation method. The transmission spectra T(λ) of the films at normal incidence were measured in the wavelength range 400–2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model (WDD). Increasing As content is found to affect the refractive index and the extinction coefficient of the As _x Se₇₀Te_30?x films. With increasing As content the optical band gap increases while the refractive index decreases. The optical absorption is due to allowed indirect transition. The chemical bond approach has been applied successfully to interpret the increase of the optical gap with increasing As content.     

Synthesis and scintillation properties of GdCl3:Ce3+ (Gd1−xCexCl3, x = 0.005–0.08)

Single crystals of GdCl₃ doped with different concentrations of Ce³⁺ have been grown using the Bridgman–Stockbarger technique and their luminescence and scintillation properties were investigated. The luminescence spectrum of GdCl₃:Ce³⁺ is complex and consists of two bands with maxima at 350 nm and 370 nm. The maximal light yield in GdCl₃:Ce³⁺ was observed at ～1 mol% of Ce³⁺ (more than 38 000 ph/MeV).     

Optical constants for Ge30− x Se70Ag x (0 ≤ x ≤ 30 at%) thin films based only on their reflectance spectra

In this paper, different homogenous compositions of Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30 at%) thin films were prepared by thermal evaporation. Reflection spectra, R(λ), for the films were measured in the wavelength range 400–2500?nm. A straightforward analysis proposed by Minkov [J. Phys. D: Appl. Phys. 22 (1989) p.1157], based on the maxima and minima of the reflection spectra, allows us to derive the real and imaginary parts of the complex index of refraction and the film thickness of the studied films. Increasing Ag content at the expense of Ge atoms is found to affect the refractive index and the extinction coefficient of the films. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. Optical absorption measurements were used to obtain the fundamental absorption edge as a function of composition. With increasing Ag content, the refractive index increases while the optical band gap decreases. The compositional dependence of the optical band gap for the Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30) thin films is discussed in terms of the chemical bond approach.