Tuning X/(TiO2)x–(SiO2)100 – x (0 < x < 40) xerogel photocatalysts

Microporous (TiO₂) _x –(SiO₂)_{100 − x} (0 < x < 40) xerogels have been produced by sol–gel methods either by partial pre-hydrolysis or reflux of tetraethoxysilane and titanium isopropoxide. These have been characterised by ²⁹Si nuclear magnetic resonance, X-ray diffraction, EXAFS at the Ti–K edge, X-ray photoelectron spectroscopy, temperature-programmed reduction, FT infrared, N₂ adsorption at 78 K (BET), transmission electron microscopy and dynamic light scattering (DLS). These were dip coated onto fused silica and characterised by atomic force microscopy and UV–visible absorption. Their photoactivity in removal of alkylphenol ethoxylate TX100 from water was less than for less porous titania. The advantages of including thermally removable PEG or PPG templates in terms of increasing surface, meso-porosity and photon absorbance at visible wavelengths to give nanoengineered photocatalytic films are described.     

XANES and USXES studies of interatomic interactions in (Co41Fe39B20)x(SiO2)1 ? x nanocomposites

The electronic structure and phase composition of (Co₄₁Fe₃₉B₂₀) _x (SiO₂)_{1 − x} nanocomposites are studied by x-ray absorption near-edge spectroscopy, which is extremely sensitive to the chemical environment of elements in multicomponent compounds. An analysis of the recorded Fe L _{2, 3}, Co L _{2, 3}, B K, Si L _{2, 3}, and O K absorption spectra demonstrates interatomic interactions between the elements of the metallic and dielectric components of the nanocomposites. As a result of these interatomic interactions, a complex multiphase system, whose electronic structure should determine the transport and magnetic properties of the nanocomposites, forms. In particular, the transformation of the fine structure of the iron L _{2, 3} spectra reflects a change in the ratio of divalent to trivalent iron in its oxides and/or silicates. CoO and complex boron oxides are found to exist in the nanocomposites. The electrical conductivity of a FeO · F₂O₃ · CoO grain embedded in the silicate-oxide medium of the nanocomposites is controlled by electron exchange between Co²⁺, Fe²⁺, and Fe³⁺ ions. The dielectric component consists of a mixture of silicon oxide and the silicates/borosilicates of transition metals. Original Russian Text ? é.P. Domashevskaya, S.A. Storozhilov, S.Yu. Turishchev, V.M. Kashkarov, V.A. Terekhov, O.V. Stogneĭ, Yu.E. Kalinin, A.V. Sitnikov, S.L. Molodtsov, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 1, pp. 135–141.     

Structure and magnetism of semiconductor crystals of the (Ga1 ? xMnx)2Se3 (x = 0?0.04) compounds

Neutron diffraction and magnetic measurements have been used to study the effect of doping with Mn³⁺ ions on the fine crystal structure of the Ga₂Se₃ monoclinic compound. It has been established that the structural state of the crystals is changed even at a relatively low doping level (x = 0.04). Arguments in favor of the fact that local Jahn-Teller distortions are responsible for the formation of the fine structure and magnetism in compounds of this class are presented.     

Structural and electrical investigation of (Ag3AsS3)x(As2S3)1?x superionic glasses

Structural studies of (Ag₃AsS₃) _x (As₂S₃)_1−x chalcogenide superionic glasses in the compositional range x = 0.3–0.9 were performed by scanning electron microscopy. Temperature and compositional dependences of transmission coefficient, electrical conductivity, and activation energy were investigated     

Electrical and magnetic properties of [(CoFeZr)x(Al2O3)1 ? x/(α-SiH)]n multilayer structures

The concentration dependences of the electrical resistivity and complex permeability of [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n multilayer structures and (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites have been studied. It has been established that introduction of a semiconductor interlayer into the (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites substantially decreases the electrical resistivity of [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n multilayer structures. The concentration dependences of the real and imaginary parts of the complex permeability of the [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n nanomultilayer structures substantially differ from those of the (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites. The real part of the complex permeability of the [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n nanomultilayer structures follows the curve with a minimum near the percolation threshold of the composite, and the imaginary part smoothly decreases as the ferromagnetic phase concentration increases. The results obtained are explained by the increase in the bifurcation temperature due to the conduction electrons of the semiconductor interlayer, which favor magnetic ordering of ferromagnetic grains.     

Magnetic anisotropy and magnetoelectric properties of Tb1 ? xErxFe3(BO3)4 ferroborates

Magnetic and magnetoelectric properties of ferroborate single crystals with complex composition (Tb_{1 − x} Er _x Fe₃(BO₃)₄, x = 0, 0.75) and with competing exchange Tb-Fe and Er-Fe interactions are investigated. Jumps in electric polarization, magnetostriction, and magnetization are observed as a result of spin-flop transitions, as well as a considerable decrease in the critical field upon an increase in the Er concentration, in a field H _c parallel to the c axis. The observed behavior of phase-transition fields is analyzed and explained using a simple model taking into account anisotropy in g factors and exchange splitting of funda-mental doublets of the easy-axis Tb³⁺ ion and easy-plane Er³⁺ ion. It is established that magnetoelectric and magnetostriction anomalies under spin-flop transitions are mainly controlled by the Tb subsystem. The Tb subsystem makes a nonmonotonic contribution ΔP _a (H _a , T) to polarization along the a axis: the value of ΔP _a reverses its sign and increases with temperature due to the contribution from the excited states of the Tb³⁺ ion. Original Russian Text ? A.K. Zvezdin, A.M. Kadomtseva, Yu.F. Popov, G.P. Vorob’ev, A.P. Pyatakov, V.Yu. Ivanov, A.M. Kuz’menko, A.A. Mukhin, L.N. Bezmaternykh, I.A. Gudim, 2009, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2009, Vol. 136, No. 1, pp. 80–86.     

Dynamics and distribution of doped holes in the CuO2 plane of slightly doped antiferromagnetic YBa2(Cu1 ? zLiz)3O6 + x (x < 0.1) studied by Cu(1) NQR

Incidence of doped holes in the CuO₂ plane on the AF state was studied by Cu(1) nuclear quadrupole resonance (NQR) in slightly doped YBa₂(Cu_{1 − z} Li _z )₃O_{6 + x} compounds. Inhomogeneous distribution of doped holes in the plane was detected in the low temperature measurements of transverse (1/T ₂) and longitudinal (1/T ₁) relaxation rates. We establish that at lower T the holes motion slows down and we estimate that the holes localize finally in restricted regions (∼3 lattice constants) in the Coulomb potential of the Li+ ions. Also we compared the hole behavior in slightly doped YBa₂(Cu_{1 − z} Li _z )₃O_{6 + x} samples with that in slightly doped Y_{1 − y} Ca _y Ba₂Cu₃O₆. A stronger trapping potential of the in-plane Li⁺ impurities was concluded as compared to slightly doped Y_{1 − y} Ca _y Ba₂Cu₃O₆ compound with out-of-plane Ca²⁺ impurities.     

Thermal conductivity of single crystals of Ca1 ? xErxF2 + x and Ca1 ? xTmxF2 + x solid solutions

The thermal conductivity of single crystals of Ca_{1 − x} Er _x F_{2 + x} (x = 0.01, 0.05, 0.07, and 0.10) and Ca_{1 − x} Tm _x F_{2 + x} (x = 0.02, 0.04, and 0.06) solid solutions is studied in the temperature ranges 50–300 and 298–673 K. With increasing content of rare-earth elements, the behavior of thermal conductivity in these solid solutions changes from the characteristic of defect single crystals to glasslike. The concentration dependences of thermal conductivity for the two systems differ insignificantly.     

Band alignment and interfacial properties of atomic layer deposited (TiO2)x(Al2O3)1?x gate dielectrics on Ge

(TiO₂) _x (Al₂O₃)_1−x (x=0.7,0.8,0.9) gate dielectrics were deposited on Ge by atomic layer deposition using trimethylaluminium and Ti isopropoxide. The interfacial properties and band alignment were investigated by means of transmission electron microscopy (TEM) and X-ray photoemission spectroscopy. High-resolution TEM results show that the (TiO₂)_0.8(Al₂O₃)_0.2 film annealed at 500°C is amorphous with sharp interface between (TiO₂)_0.8(Al₂O₃)_0.2 and Ge. The conduction-band offsets are enhanced from 1.04 to 1.40 eV with increasing Al content. Capacitance equivalent thickness of 15.8 ? for (TiO₂)_0.9(Al₂O₃)_0.1 gate dielectrics is achieved with a gate leakage current of 2.70×10⁻⁵ A/cm² at V _g=+1 V.     

Magnetic and band parameters of (3HgS)1–x(Al2S3)x (x = 0.5) crystals doped with manganese

Investigations of magnetic susceptibility (χ) of (3HgS)_1–x (Al₂S₃) _x (x = 0.5) crystals doped with manganese investigated by the Faraday method in the range of Т = 77–300 K and Н = 0.25–4 kOe demonstrate that peculiar magnetic properties can be due to the presence of clusters of the Mn–S–Mn–S type in these crystals. Based on the investigation of kinetic coefficients of the crystals performed for Т = 77–300 K and Н = 0.5–5 kOe, it is established that the crystals demonstrate conductivity of the n-type, and their electric conduction only very slightly depends on the temperature and shows a maximum, the Hall coefficient is independent of the temperature, while the temperature dependences of mobility exhibit a maximum. Using the concentration dependence of the effective electron mass at the Fermi level, the width of the forbidden band, the matrix element of interatomic interaction, and the effective mass on the conduction-band bottom are obtained. Based on investigations by optical methods, the presence of direct optical interband transitions in the crystals is established and the value of the optical forbidden band (at Т = 300 K) is determined.     

Profile of the refractive index distribution over the depth of (HfO2)x(Al2O3)1 ? x films

Capabilities of the method of laser null ellipsometry for the study of optical parameters of thin films of multicomponent alloys are demonstrated. Films of alloys (HfO₂) _x (Al₂O₃)_{1 − x} on single-crystal silicon are obtained by the chemical vapor deposition with the use of the following volatile compounds: hafnium dipivaloylmethanate (IV) and aluminum acetylacetonate (III). The selection of initial sets for their optical parameters is justified. The selected model is shown to correspond to experimental data. In films deposited from the mixture of precursors, the refractive index increases from a substrate to a film surface. Due to the separation of sources, films described by a single-layer model were deposited. This fact is indicative of the homogeneous distribution of components over the film thickness.     

Structure, ferroelectric and piezoelectric properties of?(Bi0.98?xLa0.02Na1?x)0.5BaxTiO3 lead-free ceramics

Lead-free (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La²⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi_0.5Na_0.5TiO₃ ceramics, the (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics possess much smaller coercive field E _c and larger remanent polarization P _r. Because of the low E _c (3.38 kV/mm), large P _r (46.2 μC/cm²) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d ₃₃=181 pC/N and k _p=36.3%. The depolarization temperature T _d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T _d.     

Optical characterization in Pb(Zr1?xTix)1?yNbyO3 ferroelectric ceramic system

In this work, visible photoluminescence was observed at room temperature in a sintered Pb(Zr_1-xTi_x)_1-y Nb_yO₃\mathrm{Pb}(\mathrm{Zr}_{1-x}\mathrm{Ti}_{x})_{1-y} \mathrm{Nb}_{y}\mathrm{O}_{3} perovskite-type structure system, doped with Nb using the next excitation bands 325, 373 and 457 nm. The intensity and energy of such emissions have been studied by changing the Nb concentration (0<y<0.01) and the Ti content (x), with x=0.20,0.40,0.53,0.60 and 0.80, on both sides of the morphotropic phase boundary (MPB) zone. The principal bands become visible at energies of 1.73, 2.56 and 3.35 eV. The results reveal the role of the Nb⁵⁺ ion substitutions by Zr⁴⁺ or Ti⁴⁺ ions and the symmetry presented in the rhombohedral or tetragonal side of the MPB. Raman spectra which are similar for compositions: 20/80, 40/60 and 53/47 (tetragonal phases) show nine bands, centered around 137, 194, 269, 331, 434, 550, 612, 712 and 750 cm⁻¹. The spectra for samples 60/40 and 80/20, rhombohedral phase, show significant differences, only six bands appear, centered around 124, 209, 234, 330, 549 and 682 cm⁻¹. In addition, optical absorption spectroscopy, structural and micro-structural measurements were carried out by using Uv-vis spectroscopy, X-ray diffraction and scanning electron microscopy techniques, respectively. The experimental results of band gap energy, e.g., in our samples are in accordance with the findings by J. Baedi et al. in the calculations of band structure, energy gap and density of states for different phases of Pb(Zr_1−x Ti _x )O₃ using density functional theory (DFT).     

Ferromagnetic resonance, magnetic properties, and resistivity of (CoFeZr)x(Al2O3)1 ? x/Si multilayer nanostructures

Comparative investigations of static magnetic properties, magnetoresistance, and ferromagnetic resonance data of multilayer nanostructures consisting of CoFeZr-Al₂O₃ composite magnetic layers and amorphous silicon semiconductor spacers were performed in a layer thickness range below 5 nm. The influence of layer dimension parameters and chemical peculiarities of silicon on the inner structure and type of magnetic interactions in nanostructures with 35 and 46 at % magnetic phase composite layers is discussed.     

Magnetic phase transitions in Nd1 ? xDyxFe3(BO3)4 ferroborates

The magnetic properties of ferroborate single crystals with substituted compositions Nd_{1 − x} Dy _x Fe₃(BO₃)₄ (x = 0.15, 0.25) with competing exchange Nd-Fe and Dy-Fe interactions are investigated. For each composition, we observed a spontaneous spin-reorientation transition from the easy-axis to the easy-plane state and step anomalies on the magnetization curves for the spin-flop transition induced by a magnetic field B | c. The measured parameters and effects are interpreted using a unified theoretical approach based on the molecular field approximation and on calculations performed in the crystal-field model for the rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility from T = 2 K to T = 300 K, anomalies on the magnetization curves for B | c in fields up to 1.8 T, and their evolution with temperature, as well as temperature and field dependences of magnetization in fields up to 9 T are described. In the interpretation of experimental data, the crystal-field parameters in trigonal symmetry for the rare-earth subsystem are determined, as well as the parameters of Nd-Fe and Dy-Fe exchange interactions.     

Fe K-edge X-ray resonant magnetic scattering from Ba(Fe1?xCox)2As2 superconductors

We present an X-ray resonant magnetic scattering study at the Fe-K absorption edge of the BaFe₂As₂ compound. The energy spectrum of the resonant scattering, together with our calculation using the full-potential linear-augmented plane wave method with a local density functional suggests that the observed resonant scattering arises from electric dipole (E1) transitions. We discuss the role of Fe K-edge X-ray resonant magnetic scattering in understanding the relationship between the structure and the antiferromagnetic transition in the doped Ba(Fe_1−x Co _x )₂As₂ superconductors.     

Optical properties of (In2Se3)1–x·(CuIn5Se8)x solid solutions

Single crystals of In₂Se₃ and CuIn₅Se₈ compounds and (In₂Se₃)_1–x·(CuIn₅Se₈)_x solid solutions have been grown from the melt using the Bridgman method and their composition and structure determined. It is shown that the crystals have n-type conductivity. Their transmission spectra were studied in the self-absorption edge region at 80 and 295 K. Based on the spectral measurements, the band gap width (E_g) was determined and the band gap concentration dependences were plotted. It is found that E_g varies with the x composition nonlinearly. Using the dielectric model of Van Vechten–Bergstresser and the Hill–Richardson pseudo potential model, E_g(x) was calculated theoretically.     

Modification of the optical spectra of mixed K2CoxNi1–x(SO4)2?6H2O crystals

We propose a new method for obtaining K₂Co _x Ni_1–x (SO₄)₂⋅6H₂O (x = 0, 0.4, 0.8, 1) crystals, involving the use of the chlorides (CoCl₂⋅6H₂O and NiCl₂⋅6H₂O) in an aqueous solution instead of the widely used sulfates. We have studied the transmission spectra of the grown single crystals in the range λ = 200–900 nm and the IR reflectance spectra in the 2.5–20 μm region. We have observed a change in the position and intensity of the absorption bands as a function of the composition of the crystals. Based on the Tanabe–Sugano diagrams, we determined the crystal field splitting (D_q) and its dependence on the nickel concentration. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 126–130, January–February, 2009.     

Thermal expansion of (Ba1 ? xLax)Ti1 ? x/4O3 solid solutions

Deformation and the thermal expansion coefficient of ceramic samples of (Ba_{1 − x} La _x )Ti_{1 − x/4}O₃ solid solutions (x = 0, 0.026, 0.036, 0.054) were studied in the temperature range 120–700 K. Based on an analysis of the data obtained, the temperature-composition phase diagram is refined, and the temperature dependence of the polarization is calculated. The results are discussed in combination with the dielectric measurement data. Original Russian Text ? M.V. Gorev, I.N. Flerov, Ph. Sciau, S. Guillemet-Fritsch, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 4, pp. 746–752.