Enhanced Superconductivity in Double-Doping Cu<Subscript>0.15</Subscript>TaSe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript><Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Superconducting Cu _x TaSe₂(x=0.05, 0.15) and Cu_0.15TaSe_2?x S _x (x=0, 0.5, 1, 1.5) single crystals have been systematically fabricated by a chemical vapor transport method. It is found that the double doping in TaSe₂, i.e., the simultaneous intercalation of Cu and substitution of Se by S, can substantially enhance the superconducting transition temperature. Transport property measurements give evidence of the coexistence and competition of charge density wave state and superconductivity in Cu _x TaSe₂ which provide meaningful information to understand the complex electronic states in this system. The parallel shift and the fan-shape broadening behaviors are observed in the superconducting transition curves under magnetic fields of Cu_0.15TaSeS and TaSeS, respectively, indicating an increase of coherence length and suppression of superconducting fluctuation induced by copper intercalation.     

Reflection electron-energy-loss spectroscopy of Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> thin films

The values of the product of the inelastic mean free path and the differential cross section for inelastic scattering of electrons have been determined from the reflection electron-energy-loss spectra of thin films of the Fe _x Si_{1 − x} system (0 ≤ x ≤ 1). A new approach to the quantitative analysis of components in such composite media is proposed.     

Structural Parameters and Spin Filtering Properties of Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(<Emphasis Type="Bold">M</Emphasis>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>P compound

In this work, we have explored the structural and magnetic properties of GaP-based diluted magnetic semiconductors (DMSs). Based on first-principle density functional theory (DFT) calculations and using a full potential linearized augmented plane wave (FP-LAPW) method in generalized gradient approximation (GGA), some significant structural and magnetic properties of Ga _1?x (M) _x P compound as DMS are investigated. In this compound, M is a transition element such as vanadium (V), manganese (Mn), cobalt (Co), and copper (Cu) with a concentration of X. We have calculated the structural parameters such as the equilibrium lattice constant and bulk modulus of the compound. Furthermore, the spin polarization and magnetic moments are studied. We have found that by increasing the atomic number of the transition element, the lattice constant reduces, except for that of Cu, and compressibility improved in comparison with GaP. Moreover, with X=25 %, the Ga_0.75(M)_0.25P compound becomes more stable by increasing the atomic number of the transition element M. The study of the electronic properties of the compound indicates that the main contribution in total density of states near Fermi level is related to the 3d orbitals of the transition elements and the highest magnetic moment is for Mn-doped GaP.     

Properties of amorphous Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:H (<Emphasis Type="Italic">x</Emphasis> = 0−1) films

Plasma deposition has been used to grow Si_1?x Ge _x :H(x= 0 ? 1) films, undoped and doped with PH₃ or B₂H₆, for p-i-n solar cells and other optoelectronic applications. The optical, electrical, and photoelectric properties of the films have been studied at constant hydrogenation and doping levels. The films deposited under appropriate conditions are amorphous, and three-layer solar cells fabricated from such films offer an efficiency of 9.5% at an illumination of 100 mW/cm². The photoresponse of the a-Si_{1 ? x} Ge _x :H films strongly depends on Ge content. The hydrogen concentration in the films was controlled by varying the gas phase composition and was determined from the IR absorption in the films.     

Recombination processes in solution-grown CdSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films

CdSe_1?x Te _x (0 ≤ x ≤ 0.4) films have been grown via precipitation from aqueous solutions, and their dark, photo-, and thermally stimulated conductivity has been investigated.     

Thermal expansion and isothermal compressibility of TlGaSe<Subscript>2(1 −<Emphasis Type="Italic">x</Emphasis>)</Subscript>S<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0.1, 0.2)

The temperature dependences of the thermal expansion coefficient and isothermal compressibility for TlGaSe_{2(1 ? x)}S_2x (x = 0.1, 0.2) solid solutions show an anomaly attributable to a second-order phase transition. The thermal expansion data have been used to evaluate the Debye characteristic temperature Θ, rms atomic displacement, and specific heat difference of the solid solutions.     

Hydrochemical synthesis of AgCl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Br<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

A phase-component model is proposed for the hydrochemical conversion of silver chloride to AgCl _x Br_{1 − x} solid solutions, and the corresponding quantitative relations are derived. Experimental data are used to obtain a relation between the equilibrium composition of solid solutions and that of the liquid phase at different temperatures. The possible mechanisms of solid-solution formation are considered.     

Antireflection properties of diamond-like carbon films on Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> ∼ 0.04) single crystals

The optical properties of diamond-like carbon (DLC) films obtained by plasmachemical deposition on Cd_{1 − x} Zn _x Te (x ∼ 0.04) single crystals have been studied by ellipsometry. The ellipsometric data have been interpreted within the framework of a three-layer model of the DLC film-semiconductor crystal refractory system with transition layers between the film and substrate. It is found that DLC films exhibit antireflection properties in this refractory system in the IR spectral range. It is established that the proposed antireflection film-substrate structure is stable with respect to thermal cycling and ultrasonic treatment.     

Raman spectroscopy determination of carrier concentration in <Emphasis Type="Italic">n</Emphasis>-In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As epitaxial films

We have studied in detail the coupled phonon-plasmon mode Raman spectra of n-In _x Ga_{1 − x} As with n in the range 10¹⁷ to 10¹⁹ cm⁻³. The results indicate that the behavior of the high-frequency mode L ₊ can be described in terms of coupled modes in the Drude approximation. The proposed theory and experimental data are used to estimate the carrier concentration in the solid solution and its composition.     

Thermal conductivity of Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> ≤ 0.025) solid solutions

The thermal conductivity of Er _x Sn_{1 ? x} Se solid solutions has been measured at temperatures from 80 to 360 K. The results have been used to evaluate the electronic and lattice components of thermal conductivity for elastic carrier scattering, parabolic bands, and arbitrary degeneracy. With increasing erbium content and temperature, both the electronic and lattice components decrease considerably. Long-term annealing increases both components. It follows from the present experimental data that heat conduction in Er _x Sn_{1 ? x} Se is mainly due to phonons and that the observed rise in thermal resistance with Er content is due to phonon-phonon and paramagnetic-ion scattering.     

Optical and electrical properties of Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O thin films by sol–gel method

Mg _x Zn_1−x O (0 ≤ x ≤ 0.35) thin films have been deposited by sol–gel technique and the composition related structural, electrical, and optical properties are investigated. All the films have hexagonal wurtzite structure and the separation of MgO phase occurs when x = 0.3 and 0.35. With the increase of Mg content, the densification of the films decrease and band gap values increase. The maximum band gap value reaches 3.56 eV when x = 0.15. After Mg doping the conductivities of the Mg _x Zn_1−x O films are reduced greatly and the electrical current–voltage (I–V) characteristics show nonlinearity for x > 0.15.     

Magnetic Properties of CuTi<Subscript>2−2<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>4</Subscript> Materials

The magnetic properties of semi-conductor CuTi_2−2x Cr_2x S₄ systems have been studied. The nearest neighbour J ₁(x) and the next-neighbour super-exchange J ₂(x) interactions are evaluated by using the mean field theory for this spinel CuTi_2−2x Cr_2x S₄ system. The magnetic energy, the intraplanar and the interplanar interactions are deduced. The high-temperature series expansion (HTSE) combined with the Padé approximants method (PA) is applied to this spinel system to determinate the magnetic phase diagrams, i.e. T _C versus dilution x. The critical exponents associated with the magnetic susceptibility (γ) and with the correlation length (ν) are deduced in order phase.     

Mechanism of nanostructuring in fluorite-like Ca<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>F<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript>

Nanostructuring in fluorite-like Ca_{1 ? x} La _x F_{2 + x} is shown to be associated with the precipitation of an CuAu-ordered phase. The shape of the precipitates is governed by the energetics of the {001} and {111} faces of tetragonal inclusions in highly anisotropic media and is nearly cuboctahedral. The misfit strain relaxes through the generation of twins, which nucleate along the intersection lines of {001} and {111} faces. The twins impede facial development and further growth and ordering of precipitates, thereby freezing the precipitation process in its initial stage. For this reason, the phase segregation is difficult to reveal, and Ca_{1 ? x} La _x F_{2 + x} crystals appear homogeneous.     

Synthesis of ultrafine fluorite Sr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>F<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript> powders

We have identified conditions that ensure the preparation of ultrafine Sr_{1 − x} Nd _x F_{2 + x} powders uniform in phase composition. The powders were characterized by X-ray diffraction and scanning electron microscopy. The powder particles have the form of faceted nano- and microcubes and range in size from 30–100 nm to 0.3–2.5 μm, depending on precipitation conditions.     

Thermoelectric performance of <Emphasis Type="Italic">n-type</Emphasis> (PbTe)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(CoTe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> composite prepared by high pressure sintering method

Composites of nominal composition (PbTe)_1?x(CoTe) _x (x?=?0–0.18) were fabricated by high pressure (6 GPa) sintering (773 K) method. The thermoelectric performances were investigated in the temperature range of 293–773 K. The experimental results show that CoTe utilized as the secondary phase can remarkably enhance the TE properties of PbTe, of which the highest ZT value reaches 0.88 at 473 K when x?=?0.14. The enhancement of TE performance owes much to its high electric conductivity of CoTe. Meanwhile, the high pressure sintering (HPS) samples consist of nanoparticle, which significantly enhances the boundary scattering on carriers, decreases thermal conductivity, and increases Seebeck coefficient. All the results indicate that HPS method and the addition of CoTe-composite are effective methods to enhance the thermoelectric performance of PbTe as a potential TE material.     

Structural and magnetic properties of Cr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> = 0−0.4) solid solutions

Cr_1?x V _x Te solid solutions with a hexagonal structure (NiAs type) have been obtained in the composition range x = 0?0.4 by direct melting of elemental mixtures, followed by annealing and quenching. The 80-K magnetic moment is found to decrease from 2.4μ_B in CrTe to 1.52μ_B in Cr_0.6V_0.4Te. The Curie temperature varies from 342 K to 321 K, respectively.     

Compositional effect on optical characteristics of solution grown (Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)S thin films

A good deal of information regarding the synthesis and optical properties of chemically grown (Cd_1?x Sn _x )S (x = 0.01–0.40) thin film has been reported. The growth of these films depends on various preparative parameters and deposition conditions. The reactant concentration, pH, deposition temperature, and rate of agitation were found to influence significantly the quality and thickness of the films. The photoconductive studies have been done with the help of rise and decay curves. Lifetime, mobility, and trap depth are calculated for observed parameters. Band gap measurements for the prepared films have been done with the help of optical transmission spectra using UV-VIS-IR spectrophotometer (190–1100 Å). Interesting results of PC rise and decay studies, optical absorption, and transmission spectra have been presented and discussed. Mobility is influenced significantly by Sn composition. The action spectra showed displacement in the absorption edge towards lower energy side by the addition of Sn mole content. The energy gap decreased from 2.1 to 1.9 eV for x = 0.01 and 1.85 eV for x = 0.02.     

Space charge limited conduction in a-Se<Subscript>75</Subscript>In<Subscript>25−<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

The present paper reports the d.c. conductivity measurements at high electric fields in vacuum evaporated thin films of amorphous Se₇₅In_25–xPb_x (0 < x < 10). Current-voltage (I-V) Characteristics have been measured at various fixed temperatures. In all the samples, at low electric fields, ohmic behavior is observed. However, at high electric fields (E 10⁴ V/cm), non-ohmic behavior is observed. In case of sample having 4 at.% of Pb, the experimental data fits well with the theory of space charge limited conduction (SCLC). From the fitting of the data, the density of defect states near Fermi level is calculated. Such type of behavior is not observed at higher concentration of Pb in the present glassy system.Work supported by University Grants Commission, New Delhi     

Visible-light-induced hydrogen evolution reaction with WS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>

WS₂ is a promising catalyst for the hydrogen evolution reaction. We have explored photocatalytic properties of ternary sulphoselenides of tungsten (WS _x Se _2?x ) by the dye-sensitized hydrogen evolution. WS _x Se _2?x solid solutions are found to exhibit high activity reaching 2339 μmol h^?1 g^?1 for WSSe, which is three times higher than that of WS₂ alone (866 μmol h^?1 g^?1 ). The turnover frequency is also high (0.7 h^?1 ). Such synergistic effect of selenium substitution in WS₂ is noteworthy.     

Magnetic Properties and Superconductivity in GdFeAsO<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>F<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Abstract A series of GdFeAsO_1−x F _x (x=0,0.1, 0.2, and 0.25) samples have been synthesized with conventional solid-state method. The phase purity is significantly improved by using Fe₂O₃ as the source of oxygen, compared to those prepared using Gd₂O₃ as the precursor. The lattice parameters are found to shrink with increasing fluorine doping level. The F-doped samples show a superconducting transition with T _c increasing with doping level, reaching T _c=40.1 K at x=0.25. A pronounced Curie–Weiss-like paramagnetic background, which is usually attributed to the impurity phases, is found to be independent of the fluorine doping level and proven to come from the Gd³⁺ in the GdFeAsO_1−x F _x compound with the effective magnetic moment of Gd³⁺ being μ _eff=7.83±0.05 μ_B. The extrapolated slope of dH_c2/dT|_T=Tc{dH}_{\mathrm{c2}}/dT|_{T=T_{\mathrm{c}}} in this system is about −4.5 T/K.