Direct evidence for controlled band filling in the mixed crystal NMPxPhen1−xTCNQ

Raman spectra of the segregated stack mixed crystal NMP_xPhen_1?xTNCQ and the mixed stack compound Phen TCNQ are presented. By means of the relation between charge transfer and line shift, we give for the first time a direct proof for controlled band filling in the mixed crystal series, whereas for Phen TCNQ a zero charge transfer is obtained. Raman spectra of Phenazine and the related NMP⁺ have also been measured and used for comparison.     

EXAFS of the superconducting oxide BaPb1−xBixO3

The two-valence state Bi³⁺ and Bi⁵⁺ of Bi in the semiconductor BaBiO₃ and in the BaPb_1?xBi_xO₃ (x = 0, 0.25, 0.6 and 1) system has been determined from the EXAFS spectra above the L_III-edges of Ba, Pb and Bi. Peaks in the radial distribution function up to 5 Å from the absorber have been identified through a model calculation using theoretical amplitudes and phase shifts and the interatomic distances from neutron diffraction measurements. We found indication of local disorder in the Pb-Bi sublattice for the mixed compound.     

Electrical conductivity in TlI-TiO2 composite solid electrolyte

Composite materials of formula (1−x)TlI−xTiO₂, x=0-0.7, have been prepared and studied by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and electrical conductivity. The materials were found to be binary phase systems with titania particles distributed between the grains of thallium iodide. The electrical conductivity got enhanced in the composition range x=0.1-0.5 and then decreased with further increase in the titania content. The behaviour is explained in terms of disordering phenomena at the interface regions and space-charge layers formed in the bulk grains of thallium iodide. Moreover, the increased content of titania in the system leads to the disappearance of order-disorder (β-α) phase transition in thallium iodide, which is usually observed in the pure compound. This behaviour was explained by the stabilizing effect of β-phase at high temperatures and at higher contents of titania. X-ray diffractograms do not show any indication to the presence of α-phase at ambient temperature, i.e. the phase could not be stabilized in the investigated system.     

Absorption optique du compose mixte Ga1-xAlxSb,pres du bord d'absorption

The absorption coefficient and the photovoltage of the mixed compound Ga_(1-x)Al_xSb have been measured near the absorption edge, from single crystalline layers (x = 0.30, 0.34, 0.37, 0.40, 0.56). It has been estimated that the change of nature in optical transitions occurs for x included between 0.35 and 0.40.     

Nonmonotonic variation of magnetization in Bi0.8La0.2−xPbxFeO3 (0≤x≤0.2) multiferroics

Systematic studies of crystalline structure, magnetic and ferroelectric properties have been performed on polycrystalline Bi_0.8La_0.2−xPb_xFeO₃ ceramic samples, in which x changes continuously from 0 to 0.2. Rietveld refinement of the x-ray diffraction (XRD) patterns shows that the compound crystal structure changes gradually from pseudotetragonal to pseudocubic with increasing Pb concentration. Coupled with the structural and compositional changes, magnetic ordering of the samples exhibits significantly non-monotonical variation corresponding to x. The compound remnant magnetization (M_r) and coercivity (H_c) both reach minimum values close to zero at x=0.07. This variation of magnetic property in co-doped samples can be attributed to the extent of suppression of cycloid spin structure in original BiFeO₃ with changing x. Unlike magnetic responses, the ferroelectric measurements show that the compounds have monotonical change in the remnant electric dipole polarization (P_r).     

Fine structure of the cubic semiconductor compound Zn0.9Ni0.1S

The fine structure of a single crystal of the Zn_0.9Ni_0.1S cubic compound synthesized by the chemical transport method has been investigated at room temperature using thermal neutron diffraction. It has been found that the diffraction patterns of this compound, along with strong Bragg reflections of the facecentered cubic phase, include a system of diffuse maxima, which indicate the occurrence of a local deformation of the cubic structure by the Jahn-Teller nickel ions. Results of this experiment have been compared with the previously obtained data for the lightly doped Zn_{1 ? x} Ni _x Se single crystal (x = 0.002).     

Solid-liquid equilibria for quaternary solid solutions involving compound semiconductors in the regular solution approximation

Liquidus equations for solid-liquid equilibria in quaternary systems involving compound semiconductors are presented in both thermodynamic (model-independent) and regular solution forms. A unified treatment is offered for terminal (doubly-doped binary compound, singly-doped ternary solution) as well as continuous series of solid solutions (mixing on one or both sublattices) which is facilitated by the choice of binary compounds as components in the solid. With the exception of the quaternary solid solution with mixing on both sublattices (i.e. Al_uGa_1?uP_vAs_1?v), the liquidus equations are generalizations of previous results for ternary systems. In the case of mixing on both sublattices, only three of the four possible liquidus equations are independent on account of the equilibrium among the four compound components. The required binary compound activities in the quaternary solution are deduced from a statistical treatment of a regular mixture of four kinds of atoms subject to the site restrictions of the zinc-blende lattice. The calculation of quaternary phase diagrams from binary and ternary data is discussed. Finally, it is found for the case of mixing on both sublattices that previous results, based on the decomposition of the quaternary solid solution into a binary regular mixture of ternary solids, are consistent with the present analysis.     

Magnetic properties,phase transitions and microstructural effects in mixed GdLa-based glasses

Magnetic properties of amorphous Gd_xLa_65-xCo₂₅B₁₀ are investigated from 4.2 to 300 K. AC susceptibility and magnetization measurements to 80 kOe are used to determine a phase diagram including paramagnetic, ferrimagnetic and spin-glass regions. For x ≲ 40 diffraction and susceptibility data indicate the increasing development of chemical short-range order and phase separation. An analysis of the magnetic structure and local-moment magnitudes is presented. Results of a scaling analysis for one paramagnetic-ferrimagnetic transition are discussed and some conclusions are drawn concerning the relationship between phase transitions and chemical short-range-order in ternary or higher-order magnetic glasses.     

Magnetic structure and phase diagram of the frustrated spinel Cd1−xZnxCr2Se4

In attempt to characterise the magnetic ordering in the whole composition range of the Cd_1−xZn_xCr₂Se₄ system, various magnetic measurements were performed on both crystalline and polycrystalline samples with 0?x?1. The magnetic properties of the system are typical of a ferromagnet below x=0.4 and of a complex antiferromagnet one above x=0.6. In this work the intermediate region was carefully studied. The variations of both M(T) and χ_ac at low fields suggest that transitions from ferromagnetic to Gabay–Toulouse ferromagnetic-spin-glass mixed phase at low temperature occur in the range 0.41?x?0.58. The high-temperature susceptibility measurements show that for the whole concentration range the system obeys Curie–Weiss laws. The results can be explained by the coexistence of competing interactions (ferromagnetic between nearest neighbours and antiferromagnetic between higher order neighbours) and disorder due to the random substitution between zinc and cadmium ions in the tetrahedral sites of the spinel lattice. An experimental magnetic phase diagram of the system is established.     

Al-Cr-Cu三元合金系相图的室温截面

本文用X射线粉末衍射法研究了Al-Cr-Cu三元合金系相图的室温截面。截面中出现了五个新相,称为ω₁,ω₂,ε_f,ε_x和γ_x,即共有19个单相区,41个双相区以及22个三相区。γ_x相属正交晶系,它可能是一个固定成分的化合物。 关键词：     

Structural study of CoxGe100−x alloys produced by mechanical alloying

Two alloys of the Co-Ge system were produced by mechanical alloying starting from the elemental powders in the compositions Co₂₀Ge₈₀ and Co₄₀Ge₆₀. The crystalline structures of the Co_xGe_100−x (x=20, 40) alloys obtained were investigated using the X-ray diffraction (XRD) technique. The measured XRD patterns showed the presence of the peaks corresponding to the crystalline m-CoGe phase and also to the high pressure and temperature phase c-CoGe in the as-milled sample for Co₂₀Ge₈₀, although it was milled at room temperature and pressure. For Co₄₀Ge₆₀, the crystalline Co₃Ge₂ phase was obtained, and structural data for all phases were determined by means of a Rietveld refinement procedure. The thermal stability of the phases was investigated performing a heat treatment of the alloys at 450 °C for 6 h and, after that, new XRD measurements were collected and were also studied using a Rietveld refinement procedure. The m-CoGe and Co₃Ge₂ phases seem to be very stable, but the relative amount of c-CoGe decreases a little, indicating a less stable phase, which can be explained by the fact that it is produced usually under extreme conditions.     

Structural stability and magnetic properties of Bi1−xLa(Pr)xFeO3 solid solutions

In this work, X-ray diffraction data taken on Bi_1−xLa_xFeO₃ solid solutions are used to verify the following structural phase transitions: “polar rhombohedral-antipolar orthorhombic” at x≈0.16 and “commensurate-incommensurate” within the orthorhombic phase at x≈0.18. In contrast, in the Bi_1−xPr_xFeO₃ series, the polar rhombohedral phase transforms into an antipolar orthorhombic one at x≥0.13. The polar rhombohedral phase near the morphotropic phase boundary exhibits an isothermal transformation into an antipolar orthorhombic phase, though the transformation occurs much faster in the case of La-doped compounds. The incommensurate structural phase was not detected in Bi_1−xPr_xFeO₃ solid solutions. The ternary structural phase diagram is constructed for (Bi,La,Pr)FeO₃ systems. In addition, the polar rhombohedral phase exhibits a magnetic field-induced transition from the modulated antiferromagnetic state into a homogeneous weak ferromagnetic state whereas the antipolar phase is a weak ferromagnetic state in the absence of an external field.     

Growth features at competing nucleation of quantum dots and nanopits in Si-Ge-C ternary system

The continuum elasticity model is applied to quantitatively investigate the growth features and nucleation mechanism of quantum dots (QDs), nanopits, and joint QDs-nanopits structures in SiGeC ternary systems. We determined the critical concentrations of carbon, x = 0.08 for Si_1?x C _x and y = 0.0033 for Si_1?x?y Ge _x C _y at the concentration of germanium x = 0.467, when the growth mode changes from, respectively, nucleation of QDs to formation of nanopits. We have shown that the increase in the carbon concentration in a SiC binary system and of germanium concentration in a SiGeC ternary system leads to a decrease in the critical size of QD. The free energy of mixing for Si_1?x?y Ge _x C _y ternary system was calculated and studied and its 3D sketch plotted. It is demonstrated that incorporation of carbon into Si and Ge up to background impurity concentration is energetically preferable, which explains the experimentally detected ??contamination?? of silicon and germanium crystals by carbon during the growth in the graphite crucible.     

Characterization of multiferroic LiTMxCu2−xO2 (TM=Ni and Zn) single crystals

We investigate a series of single crystalline samples of LiT_MxCu_2−xO₂ (T_M=Ni and Zn) grown by floating-zone technique. As-grown crystals showed a clear X-ray diffraction pattern of pure(single) phase. These crystals exhibit varied magnetic and electrical properties owing to successful incorporation of Ni and Zn dopants.     

Surface phonon–polaritons in rectangular quantum wires of polar ternary mixed crystals

In this paper, the dispersion relations of surface phonon–polaritons in freestanding rectangular quantum wire systems of polar ternary mixed crystals are derived. The numerical calculations for Al_xGa_1−xAs and Zn_xCd_1−xSe quantum wire systems are performed. The results reveal that the frequencies of surface phonon–polariton modes are sensitive to the geometric structures of the quantum wires, the wave-vectors in z-direction, and the compositions of the ternary mixed crystal materials. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface phonon–polariton modes are also discussed.     

Phase transformation in (0.90−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3-0.10PbZrO3 piezoelectric ceramic: X-ray diffraction and Raman investigation

Piezoelectric ceramics with compositions of (0.90−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃-0.10PbZrO₃, x=0.28, 0.31, 0.34, 0.37, 0.40 and 0.43, were prepared using the conventional columbite precursor method, and their structural phase transformation and piezoelectric behaviors near the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO₃ content. X-ray diffraction (XRD) results demonstrate that the structure of the ceramics experiences a gradual transition process from rhombohedral phase to tetragonal phase with the increasing of PbTiO₃ content, and that compositions with x=0.34-0.40 lie in the MPB region of this ternary system. A Raman spectra investigation of the ceramic samples testified to the transformation process of rhombohedral phase to tetragonal phase by comparing the relative intensities of tetragonal E(2TO₁) mode and rhombohedral phase R_h mode. The structure information was also correlated to the parabola change of the piezoelectric constant; the maximum piezoelectric constants were obtained near the MPB region.     

Nanoscale ion-beam mixing in Au–Si and Ag–Si eutectic systems

MeV ion induced mixing in the nanoscale regime for Au and Ag nanoislands on silicon substrates has been studied. Au and Ag nanoislands are grown on silicon substrates at room temperature and irradiated with 1.5-MeV Au²⁺ ions at various fluences. Cross-sectional high-resolution transmission electron microscopy and Rutherford backscattering spectrometry (RBS) are used to study the ion-beam mixing in Au/SiO_x/Si and Ag/SiO_x/Si systems. We observe a metastable mixed phase for the Au–Si system at a fluence of 1×10¹⁴ ionscm^-2, while no mixed phase is formed for the Ag–Si system. For both Au–Si and Ag–Si systems, a part of the islands is pushed into the substrate. The mixed phase of the Au–Si system is found to be crystalline in nature. The higher eutectic temperature and lower heat of mixing of the Ag–Si system compared to the Au–Si system could be responsible for the lack of mixing and silicide formation in the Ag–Si system. PACS 61.80.Jh; 61.82.Rx; 68.37.Lp; 64.75.+g; 61.46.+w     

Gd-doped SnO2 nanoparticles: Structure and magnetism

Gd-doped SnO₂ nanoparticles were chemically prepared doping 0-12.5% Gd into SnO₂ and calcined at 600 °C. X-ray diffraction and Fourier transformed infrared spectroscopy measurements show the formation of single phase of Sn_1−xGd_xO₂ up to x=0.0625 while at x=0.125, an additional secondary phase of tetragonal GdO₂ (not cubic Gd₂O₃) is detected. The transmission electron microscopy studies show that the individual particles are single crystalline with an average size in the range of 10-12 nm. Magnetization measurements show the absence of ferromagnetic and antiferromagnetic ordering in all samples; however surface spin effects and enhanced Gd-O-Gd interactions are proposed to account for the observed magnetic properties of the samples.     

Superconductivity of some splat cooled Nb-Au-Pt alloys

Measurements of the superconducting transition temperatures are made on some ternary alloys of non-stoichiometric composition e.g. Nb_2.3 Au_(1?x )Pt _x and Nb₄Au_(1?x)Pt _x prepared by splat cooling technique. Lattice constants of the A-15 phase are measured by x-ray diffraction technique. Optical micrographs are used to check the distribution of different phases in these alloys. Results are compared with the alloys of same compositions in as cast and annealed conditions.     

Structure and magnetic properties of Fe96−x Zr x B4 nanowire arrays

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