Concentration or modulation layering of perfect single crystals Bi2Sr2?xLaxCuO6+δ and Bi2?yPbySr2?xLaxCuO6

Precision structural studies of layering of perfect crystals Bi ₂ Sr _2−x La _x CuO _6+δ (BSLCO) ∼ 10 μm thick, grown by free growth within crystallized melt cavities, detect a macrolayer structure with each layer up to 0.1 μm thick. In the lanthanum concentration range x = 0.6−0.8, only modulation layering is observed. In the concentration range x = 0.3−0.5, either layers with two different lanthanum concentrations, but with the same modulated superlattice type, or layers with the same lanthanum concentration, but with two different modulated superlattice types are observed. At low lanthanum concentrations (0 < x < 0.26), layering into two or even three layer types with different lanthanum concentrations are almost always observed. Modulation suppression when lead is added to a mixture leads to the same layered structure of samples, but with appreciable variations in lattice parameters in the ab plane of individual layers and a and b axis rotation by several degrees with respect to each other in these layers. Thus, the superlattice in BSLCO single crystals stabilizes their composition in the ab plane, and inevitable variations in growth conditions lead to the layered structure of such crystals. Original Russian Text ? V.P. Martovitsky, A. Krapf, 2008, published in Kratkie Soobshcheniya po Fizike, 2008, Vol. 35, No. 3, pp. 29–38.     

Influence of structural deformations on the magnetic properties of Jahn-Teller complexes of divalent copper in CaxSr1−x F2 mixed crystals

Crystals of variable constituency Ca_xSr_1−x F₂:Cu (0⩽x⩽0.05, x≅0.5, 1.0⩾x⩾0.95) are investigated by EPR and x-ray structural analysis. The electron-Zeeman, intrinsic hyperfine, and ligand hyperfine interaction parameters are determined; they characterize the magnetic properties of the copper paramagnetic complexes formed in the crystals. Models of the molecular structures of these complexes are discussed, along with the influence of structural deformations and vibronic interactions on their magnetic properties. Fiz. Tverd. Tela (St. Petersburg) 40, 445–451 (March 1998)     

Measurement of the differential and integral distribution of diffuse x-ray scattering intensity from defects in thin strained layers

Double-and triple-crystal diffractometry have been used to study structural perfection of a ∼1 μm-thick Ga_1−x In_xSb_1−y As_y epitaxial film (x=0.9, y=0.8) on GaSb. It is shown that scattering from samples of this system can be divided into coherent and diffuse. The arrangement of reciprocal-lattice points of the film and substrate in the two-dimensional intensity distribution for asymmetrical reflections argues for the absence of elastic-strain relaxation. No dislocation networks are formed, and the diffuse scattering is produced by Coulomb-type defects. Localization of diffuse scattering in reciprocal space suggests that these defects reside in the epitaxial film. The diffuse-scattering distribution in asymmetrical reflections is shown to be anomalous; namely, it extends in a direction parallel to the surface and is split into two maxima. Schemes have been proposed and realized for measuring integral distributions of diffracted intensity along the surface and perpendicular to it, and their potential for studying diffuse scattering from defects is explored. Fiz. Tverd. Tela (St. Petersburg) 39, 1188–1193 (July 1997)     

Formation and growth of an α-PbF2 phase during the plastic deformation of β-PbF2 crystals

The microstructure of strained β-PbF₂ crystals is investigated by optical and scanning electron microscopy. It is established that the α-PbF₂ previously observed by x-ray diffraction methods during the straining of cubic PbF₂ nucleates predominantly on structural defects like slip lines and bands. The kinetics of the growth of α-PbF₂ particles during the straining of β-PbF₂ crystals and during a postdeformation anneal is investigated. The results of the experiments point to the involvement of diffusion in the growth of α-PbF₂. Fiz. Tverd. Tela (St. Petersburg) 39, 640–646 (April 1997)     

Characterization of multilayer systems by high-resolution x-ray diffraction

The x-ray diffraction pattern of MBE-grown Ga_1–x Al _x As/GaAs superlattices has been measured withd-spacing resolutiond/d approaching 17000, corresponding to about 8500 Å^–1. The resolution was achieved by employing a highly dispersive monochromator consisting of a pair of fivefold reflecting grooved silicon crystals which delivers about 10⁴ photons s^–1 to the sample. Detailed information like the presence of buffer layers, the molar fractionx, the numberp of layers, the superlattice periodt _p , and the component layer thicknessest ₁ ,t ₂ are extracted from the measured pattern by comparing it with the pattern calculated from the dynamical theory for layer structures. In addition, the influence of disorder on the determination of the above superlattice parameters is investigated by including two different models of disorder.     

GexSi1-x/Si超晶格的X射线小角衍射分析

用分子束外延生长了23周期的Ge_xSi_1-x/Si超晶格,用计算机控制的衍射仪(CuK_a辐射)测量了X射线衍射曲线,共观察到13级超晶格结构的衍射峰。超晶格的周期和Ge平均含量可以根据考虑折射修正的布喇格定律得出。用光学多层膜反射理论分析衍射曲线可以确定超晶格的结构参数,第2级衍射峰与第一级峰的强度比对应于超晶格两种材料的相对厚度变化非常灵敏,通过比较实验和计算的I₂/I₁值,可以确定Si,Ge_xSi_1-x层的厚度以及合金组份x。用光学多层膜反射理谁计算得到的衍射曲线与实验曲线趋于一致。 关键词：     

Room-temperature ferromagnetism in lightly Cr-doped ZnO nanoparticles

Zn_1−x Cr _x O (0≤x≤0.15) nanoparticles were synthesized by an auto-combustion method and characterized by x-ray diffraction and Raman scattering techniques. The solubility limit for Cr in ZnO was determined as x≈0.03. Room-temperature ferromagnetism (RT-FM) was observed in lightly Cr-doped ZnO nanoparticles with x=0.01 and 0.02. Raman scattering spectra of the lightly Cr-doped and Co-doped ZnO were studied and compared. The enhancement of both the magnetization and the intensity of Raman scattering peak associated with donor defects (Zn_i and/or V_O) and carriers indicates that light Cr doping in ZnO could be an effective way to achieve pronounced RT-FM and the ferromagnetism is closely related to the dopant-donor hybridization besides the ferromagnetic Cr–O–Cr superexchange interactions.     

X-ray diffractometry and electrical conductivity of the ceramics LaSrAl(Cu,Ni)O4

A continuous series of solid solutions LaSrAL_1−x Me_xO₄ (Me = Cu, Ni) has been investigated by x-ray diffractometry and by electrical conductivity measurements. The results are of interest from the standpoint of the theory of close-packing, percolation theory, and the theory of the cooperative Jahn-Teller effect. Fiz. Tverd. Tela (St. Petersburg) 39, 985–990 (June 1997)     

Weak ferromagnetism and oxygen ordering in La2CuO4+x single crystals

The changes produced in the magnetic properties and structure of La₂CuO_4+x (0< x<0.015) single crystals by doping with oxygen are investigated by differential magnetic susceptibility and x-ray diffraction methods. It is found that the appearance of a weak ferromagnetism in weak fields H<50 Oe is accompanied by a lowering of lattice symmetry as a result of the oxygen ordering. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 159–162 (10 August 1997)     

Electron spin resonance of localized copper states in Sr1?xAxCuO2 ceramics (A = Li+, K+, La3+; x ≤ 0.15)

The orthorhombic modification of SrCuO₂ ceramics and its derivatives Sr_1−x A _x CuO₂ (A = Li⁺, K⁺, La³⁺) were studied using the ESR and x-ray diffraction methods. Orthorhombic and axial-symmetry paramagnetic centers caused by oxygen defects in samples were detected. From comparing the ESR and x-ray phase data, it follows that the oxygen distribution in ceramics is inhomogeneous. __________ Translated from Fizika Tverdogo Tela, Vol. 47, No. 8, 2005, pp. 1482–1485. Original Russian Text Copyright ? 2005 by Ivanova, Jacyna-Onyszkiewicz, Augustyniak-Yablokova, Yablokov, Shustov.     

Magnetic phases of FexV1−x S and their electronic structure

A study has been made of the Fe_xV_1−x S solid solutions with 0<x<0.5. For the compounds with x>0.1, x-ray diffraction analysis discloses a V₅S₈ superstructure. Samples with x>0.1 are magnetically ordered at room temperature. The concentration dependences of resistivity and magnetization exhibit sharp peaks for x=0.1 and x=0.2, respectively. The main features of the structure and electronic properties have been qualitatively explained in terms of the three-band exciton-insulator model, and the maxima in resistivity and magnetization are assigned to the formation of localized magnetic moments with S=1, which become delocalized with increasing x. Fiz. Tverd. Tela (St. Petersburg) 40, 1890–1893 (October 1998)     

Features of the resonant interaction of moving neutral atoms and clusters with superlattice surface

Features of the interaction of moving neutral atoms, molecules, and clusters with a superlattice field (for example, the system of linear magnetic and electric domains) are considered. It is shown that the character of the particle motion depends on the ratio of the frequency ω₂₁ of the internal electromagnetic resonance to the bounce frequency Ω _s determined by the superlattice period, the velocity of the particle motion, and the possible moments of the particle in the ground d ₁₁ and excited d ₂₂ states. The conditions for regimes of attraction and repulsion of particles by the superlattice are considered. The preconditions for formation of a one-dimensional potential well located far from the superlattice and for stable channeling of neutral and charged particles in this well are also considered. Depending on the ratio of ω₂₁ to Ω _s , particle sorting and beam separation occur during interaction of the multicomponent beam consisting of different particles with the superlattice field.     

Magnetic state of nickel-zinc ferrites at high zinc concentrations

Neutron diffraction and magnetic methods are used to investigate ferrites from the system Zn_xFe_1−x [Ni_1−x Fe_1+x ]O₄. In these investigations, no diffraction effects were observed that would indicate ordered positions for the perpendicular projections of spins at 4.2 K over the entire ferrimagnetic range of concentrations x. However, the high-field magnetic susceptibility and intense small-angle scattering of neutrons observed at helium temperatures in samples with x>0.45 are evidence of local angular structures with effective sizes of 1–10 nm. The temperatures at which these local angular structures are disrupted are determined. Fiz. Tverd. Tela (St. Petersburg) 40, 1503–1504 (August 1998)     

Magnetic structure of Ce<Subscript>2</Subscript>Fe<Subscript>17 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

The magnetic structure of intermetallic compounds Ce₂Fe_{17 − x} Mn _x (0 ≤ x ≤ 3) was studied using neutron diffraction. The neutron diffraction patterns measured at 4.2 K contain satellites indicating a modulated structure with the wave vector k = [0, 0, τ]. As the concentration x increases, the value of τ increases, while the average magnetic moment of Fe/Mn atoms decreases. A change in the magnitudes of the average magnetic moment and wave vector k is explained by competition between exchange interactions at distances of nearest neighbor transition element atoms.     

Temperature Dependence of the Transmission Spectra of Silicate Glasses Containing CdS<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Semiconducting Nanocrystals

The transmission spectra of silicate glasses containing CdS_{1 − x} Se _x semiconducting nanocrystals of various sizes are investigated in the temperature range 20–300°C. It is shown that for explaining optical properties of these materials, not only the nanocrystal sizes, but also the structural changes occurring in nanocrystals during their formation must be taken into account.     

Experimental study of the energy gap in the spin-wave spectrum in Co/Pd multilayer films

The energy gap appearing in the spin-wave spectrum as a result of Bragg scattering by the modulation period q=2π/(d ₁+d ₂) of a one-dimensional superlattice is observed by the method of spin-wave resonance in Co/Pd multilayer films. It is shown that this gap is asymmetric: The “positive” deviation is from two to three times greater than the “negative” deviation. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 938–941 (25 June 1996)     

Determination of the parameters of semiconductor quantum dots in glassy matrices from the absorption and luminescence spectra and from saturation of the optical absorption

Optical methods are described for determining the parameters of semiconducting quantum dots synthesized in a glassy borosilicate matrix. The limitations of these methods and the magnitudes of their errors are analyzed. The parameters of CdS_xSe_1−x nanocrystals in the commercial glasses KS-10, OS-12, Corning 2–61, and other experimental samples are determined. Fiz. Tverd. Tela (St. Petersburg) 39, 1865–1870 (October 1997)     

Influence of parity-forbiddenness in the onset of mixed valence state in Sm1−x GdxS

The electronic structure of Sm and Gd in Sm_1−x Gd_xS has been experimentally studied by the x-ray shift method. Besides the well known strong increase of Sm valence at x≈0.15 (associated with the electronic transition to the mixed valence state), a decrease of Sm valence for x⩾0.9 has been observed for the first time. This phenomenon is explained as due to the 4f-5d hybridization on neighboring Sm atoms involved in the onset of the mixed valence state, and is interpreted as a manifestation of parity violation forbiddenness. Fiz. Tverd. Tela (St. Petersburg) 39, 1017–1019 (June 1997)     

Titanium K-edge absorption structure in Ti1−x NbxO2

The fine structure in the titanium x-ray K-edge absorption has been measured in Ti_1−x Nb_xO₂ mixed dioxides (x=0–0.1) with rutile structure in a laboratory-type spectrometer by total electron quantum-yield measurement. The position of the XANES lines is shown to be in good agreement with classical x-ray absorption spectra obtained in transmission. The structure and main features of the XANES spectra, including the effects of impurities and manyelectron excitations, are discussed. It is suggested that the intensity of the B peak characteristic of the titanium K edge depends on the Nb concentration and correlates with the charge state of titanium ions. Fiz. Tverd. Tela (St. Petersburg) 41, 894–896 (May 1999)     

Superconductivity, Seebeck coefficient, and band structure transformation in Y1−x CaxBa2Cu3−x CoxOy (x=0–0.3)

The temperature dependences of the resistivity and of the Seebeck coefficient S is studied in three series of Y_1−x Ca_xBa₂Cu_3−x Co_xO_y samples (x=0–0.3) differing in oxygen content. It was found that the critical temperature decreases for y≈7.0, and S(T=300 K) increases with doping, whereas oxygen deficiency results in a nonmonotonic variation of these quantities with increasing x. The band structure parameters have been determined from an analysis of the S(T) relations using a phenomenological theory of electron transport. It was found that an increase in x results in a gradual increase in band asymmetry, which is caused by calcium-induced creation of additional states in the band responsible for conduction in the normal phase. An analysis has shown that high impurity concentrations in oxygen-deficient Y_1−x Ca_xBa₂Cu_3−x Co_xO_y samples bring about an additional ordering of the structure, which may be caused by formation of a cobalt superlattice. It has also been shown that, in the case of Ca and Co codoping, the dependence of critical temperature on effective conduction-band width coincides with the universal correlation relation observed in the YBa₂Cu₃O_y system with single substitutions in various lattice sites. Fiz. Tverd. Tela (St. Petersburg) 41, 1363–1371 (August 1999)