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.     

Codes over <Emphasis Type="Bold">Σ</Emphasis><Subscript>2</Subscript><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> and Jacobi forms over the Quaternions

We introduce codes over the ring We relate self-dual codes over this ring to quaternionic unimodular lattices and to self-dual codes over via a gray map. We study a connection between the complete weight enumerators of codes over the quaternionic ring _2m and Jacobi forms over the half-space of quaternions. This motivates us to construct an algebra homomorphism from a certain invariant polynomial ring, where the complete weight enumerators belong, to the ring of Jacobi forms over the quaternions. Higher genus modular forms over the quaternions are also constructed using joint weight enumerators of codes.This research was partially supported by KOSEF R01-2003-00011596-0Some of the results of this paper were presented at the IEEE Information Theory Workshop, April, 2003     

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.     

Phase transformation of <Emphasis Type="Italic">p</Emphasis>-Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GeAs<Subscript>2</Subscript> single crystals at 5.5 GPa

The electrical resistivity and Hall coefficient of oriented single-crystal p-Cd_{1 − x} Mn _x GeAs₂ samples have been measured at high pressures. The results indicate that the crystals undergo a reversible structural transformation at 5.5 GPa, which is independent on the sample orientation.     

Preparation and Properties of Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te

Mn _x Hg_{1 ? x}Te (x = 0.05, 0.12) single crystals were grown by solid-state recrystallization, and their axial and radial homogeneity was assessed by optical, electrical, and electron-microscopic measurements. The crystals are p-type, with a hole concentration of (4.3–5.3) × 10²² m^?3 and Hall mobility in the range (410–570) × 10^?4 m²/(V s).     

Ordering and twinning in the nonstoichiometric phase La<Subscript>1 − <Emphasis Type="Italic">y</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>F<Subscript>3 − <Emphasis Type="Italic">y</Emphasis></Subscript>

The nonstoichiometric phase La_{1 ? y} Ca _y F_{3 ? y} with a LaF₃-related structure has been studied by electron diffraction. In addition to diffraction features corresponding to twinning on the (001) and {1\(\bar 2\)0} planes, typical of LaF₃, evidence has been found for twinning on the {101} and {102} planes. This behavior is accounted for by the formation of ordering domains with an ordering direction inclined to mirror planes. It seems likely that ordering domains determine many of the properties of nonstoichiometric phases.     

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.     

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.     

Homogeneity of high-resistivity <Emphasis Type="Italic">p</Emphasis>-Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>〈Au〉 crystals

p-Si_{1 ? x} Ge _x crystals have been diffusion-doped with gold. Gold diffusion in the p-Si_{1 ? x} Ge _x 〈Au〉 samples and their electrical properties have been studied. The results demonstrate that the highest gold concentration in the crystals can be achieved in the temperature range 1000–1050°C. An expression has been derived which indicates that, all other factors being the same, compensation with Au, an amphoteric impurity, insures better homogeneity compared to codoping with acceptor and donor impurities. The hole concentration homogeneity in gold-compensated samples is at the same level as or even better than that in the uncompensated material.     

Synthesis and Characterization of Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript>3</Subscript> Superconductor

In this paper, we characterized the microstructure and superconducting properties of Cu-doped NiBi₃ samples. The polycrystalline Ni_1?x Cu _x Bi₃ (0 ≤ x ≤ 0.10) samples were prepared using a solid-state reaction method. The crystal structure and unit cell parameters were determined by Rietveld refinement of powder X-ray diffraction. The data showed that the main phase present corresponded to NiBi₃ without dependence on the Cu concentration, but with small quantities of Ni and Bi. The SEM and AFM measurements revealed that the main phase was inhomogeneous at microscopic level, with Bi richer regions in comparison to other regions. However, Raman spectroscopy results did not show significant changes in the spectra with Cu doping and in different regions of the samples. Another finding was that regardless of Cu doping, the superconducting transition temperature was 4.05–4.06 K.     

Synthesis of Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> spinels at low temperature and atmospheric pressure

In order to synthesize cobalt-based spinel oxides, air was bubbled through aqueous hydroxides suspensions of cobalt and zinc with atomic ratios of Co:Zn = 100:0, 85:15, 67:33 (precisely 2:1), 50:50, 30:70, 15:85, and 0:100 at 70 °C and atmospheric pressure. When cobalt was absent in the suspensions, hexagonal ZnO nanocrystals with ca. 82.2 nm size were observed, whereas cubic Co₃O₄ ones with ca. 52.7 nm were seen when zinc was not present. Zinc-contained cobalt spinel oxides, i.e., Zn _x Co_3?x O₄ (x = 0–1), were obtained when both hydroxides were present, e.g., spherical nanoparticles with ca. 107.6 and 85.0 nm diameters were observed for Co:Zn = 50:50 and 67:33, respectively. The lattice constant, a, for the cubic spinel increased with the increase in zinc atomic %, suggesting the increase in zinc concentration in the spinel. The Zn _x Co_3?x O₄ synthesized was normal spinel with a cubic crystal structure, whereas it was also suggested that a very small portion of zinc ion was incorporated into the octahedrally coordinated sites (inversion of spinel). BET surface area of the synthesized catalyst increased with increasing the cobalt atomic % except for Co:Zn = 67:33, for which local minimal surface area was obtained. Oxygen storage capacity of the catalyst was the largest for Co:Zn = 85:15 at 150 and 200 °C, whereas it was for 50:50 at 250 °C. After reducing the synthesized catalysts with hydrogen, metallic cobalt was formed on zinc oxide. CO chemisorption number on the cobalt was the largest for Co:Zn = 67:33, for which the smallest metallic cobalt diameter was also obtained. On the other hand, catalytic CO₂ hydrogenation activity and methane selectivity were the highest for Co:Zn = 50:50, suggesting that zinc oxide as a basic support played an important role in the hydrogenation of acidic CO₂. It was also shown that the catalytic hydrogenation activity and the methane selectivity were higher for the catalysts prepared by the present liquid-phase approach than for those prepared by conventional coprecipitation and impregnation methods, which were ascribed to larger surface area and number of active sites for the former preparation technique than for the latter two.     

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.     

Structural and Superconductivity Properties of BaFe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>2</Subscript>

Extraordinary magnetic behaviors, resistivity properties, and lattice parameters of the main sample BaFe₂As₂ and BaFe_2?x Pt _x As₂ in the variation of x from 0 to 0.4 with the step of 0.1 were investigated. The bulk materials have been prepared by the solid-state reaction method and sealed into a quartz tube. The crystal structure of all samples exhibited the ThCr₂Si₂-type crystal structure which is in harmony with earlier studies in the literature. The superconducting states with magnetization measurements have been detailed in the wide temperature range 5–170 K, up to a field of 20 Oe. Increasing Pt and decreasing Fe elements in the BaFe_2?x Pt _x As₂ compound deteriorated superconductivity. Using magnetization measurement data, we present the variation of superconducting critical temperature (T _c) correlating with a Pt dopant rate from x = 0 to x = 0.4. The dopant rate of x = 0.3 exhibited the limit rate for maximum T _c; deterioration of superconductivity was revealed with a dopant rate of more than x = 0.3. This should be explained by varying T _c related to a lattice shrinking and pressure effect (geometric factor).     

New Quaternary Half-Metallic Materials of the <Emphasis Type="Italic">Z</Emphasis><Subscript><Emphasis Type="Bold">t</Emphasis></Subscript> − 28 Rule in LiMgPdSn-Type Heusler Alloys

This paper presents first-principles calculations with the full-potential linearized augmented plane-wave method to study a series of LiMgPdSn-type Heusler alloys. The chemical formula is XX^′YZ, where X = Fe, Co, or Ni; X^′ = Mn; Y = Cu or Zn; and Z = Si, Al, Ga, or Ge. Eight compounds are found to be half-metallic magnets and obey the Slater–Pauling rule with the total number of valence electrons (Z _t) of 28. The half-metallic band gap in CoMnZnSi compounds reaches its maximum of 0.66 eV. CoMnCuGe and CoMnZnGa can be transformed from a quasi-half-metallic alloy to a half-metallic alloy by employing sufficient compression stress.     

Structure and Superconductivity of (MgB<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>C<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>0.97</Subscript>Cu<Subscript>0.03</Subscript>

A series of samples of (MgB_2−x C _x )_0.97Cu_0.03 (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) and MgB₂ were synthesized by a solid state reaction method. The structure, superconducting transition temperature and transport properties of the samples were studied by means of X-ray diffraction (XRD) and resistivity measurements. It is found that the c-axis of the lattice remains unchanged with increasing C doping, while the a-axis shows a small decrease. The T _c of the samples steadily decreases with increasing C doping. It is suggested that the chemical pressure effect plays a more important role influencing the normal state transport and T _c than the change of carrier concentration.     

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.     

Structure and photoelectric properties of Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> epilayers

Epitaxial layers of n-type Si_{1 − x} Snx (0 ≤ x ≤ 0.04) solid solution were grown by liquid phase epitaxy from tin-based solution melt confined between two horizontal Si(111) single crystal silicon substrates. The structure of epilayers was determined and the photosensitivity spectra of pSi-nSi_{1 − x} Snx (0 ≤ x ≤ 0.04) structures were studied at various temperatures. It is established that Si_0.96Sn_0.04 films have a perfect single crystal structure with (111) orientation and a subgrain size of 60 nm. The photosensitivity edge of the pSi-nSi_0.96Sn_0.04 structure is shifted to longer wavelengths as compared to that of the pSi-nSi structure. The photosensitivity of the pSi-nSi_0.96Sn_0.04 structure in the impurity absorption range depends on the temperature.     

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.     

Preparation and tunable photoluminescence of alloyed CdS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> nanorods

Ternary alloys of CdS _x Se_1−x nanorods have been synthesized by the thermal treatment of Cd²⁺ dispersed polyethylene glycol 2000 gel (PEG2000) with ethylenediamine solution of sulfur and selenium in a sealed system at 180 °C for 24 h, during which the proportion between S and Se in the nanorods was controlled by the ratios of every starting material to each other. The alloyed ternary CdS _x Se_1−x nanorods are highly crystalline without any other phase. The optical property these nanorods could be manipulated by modulating the composition of S and Se.