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Gallium sulfide single crystal is a potential material for nonlinear optics. Due to its high non-linearity it can be used as a material for IR and THz frequency converters. In the present work GaS bulk crystals of precise stoichiometry and high quality were melt grown using vertical zone melting. Elementary content of the crystals was tested using electron probe microanalysis, phase composition and unit cell parameters were studied using X-ray powder diffraction (XRD), morphology of the cleavage plane and layered structure of a cross section normal to the growth axis were studied using light microscopy, morphology of impression under an indenter tip was imaged by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Various mechanical properties, such as hardness, Young modulus of nanoindentation, residual indentation depth, contributions of elastic and plastic parts to total deformation were studied in the nanoindentation experiments. Experiments on microindentation of GaS single crystals were carried out for comparison. It was found that nanoindentation hardness and elasticity modulus depend non-monotonously on peak load. The results confirm that despite of their layered structure, GaS crystals have high micro- and nanohardness and plastic deformation ability, which provide their suitability to be processed for optical elements.

Powder and polycrystals synthesized from Ga, Se, Er components, as well as GaSe and GaSe:Er single crystals grown from melt in argon atmosphere and in vacuum, respectively, are studied. The growth and quenching conditions used in this work provide 2.5 times increase in solubility of erbium in GaSe matrix and a decrease in number of phases to GaSe and Er2Se3, oppositely to multiphase GaSe:Er alloys known from literature. For the first time Er2Se3 phase was detected by XRD in GaSe crystal doped with 1 at%Er. Possible orientation relations are derived for Er2Se3/GaSe epitaxial pair. It has been shown that stretched reflections in electron micro diffraction patterns and scattering of maximums in x-ray diffraction patterns are bound to stacking faults, which appear owing to thin interlayers of δ-GaSe polytype in e-GaSe matrix of the melt-grown crystals. Morphology of growing crystal surface is studied. Photoluminescence spectra of pure and erbium-doped GaSe display intense photoluminescence bands, which are, presumably, associated with defect states in band gap of GaSe. It is shown that doping with Er has a strong effect on photoluminescence intensity and on its spectral composition. The measured 1.7 times increase in Vickers microhardness (up to 400 MPa) with respect to pure GaSe is due to solid solution hardening and to precipitation.

The multilevel nature and plasticity of memristor structures based on bismuth selenide microcrystals (of the “flake” type), which are controlled by the rewriting voltages Vset / Vreset are investigated. It was shown by numerical simulation that the switching is caused by the barrier properties of the defective layer, consisting of two sublayers having different thicknesses, as well as different electrical and thermal conductivities, overheating phenomena have been also taken into account. The change in the device resistance both at ON-OFF and at OFF-ON transitions begins at approximately the same absolute value of the threshold electric field of the order of 105 V/cm. Modulation of the barrier formed at the interface between a metal and a strongly doped semiconductor is the most likely model for resistive switching in bismuth selenide-based structures.

The polymorphic transition from hexagonal to monoclinic phase was studied for the first time in melt grown GaTe crystals. The polymorphic transition goes as a non-variant process at a constant temperature and pressure without any changes in composition. Though the character of the phase transition is apparently diffusive, no interface or grain boundaries are detected. After completion of the phase transition the whole volume of the crystal remains a single crystal. The cleavage plane is preserved and proves to be a habit plane between the hexagonal and monoclinic phase. Reflections in Laue patterns are sharpened and peaks in X-ray diffraction patterns are narrowed upon the transition, which is attributed to relaxation of internal stresses. Annealing of the transformed monoclinic GaTe at 1023 K followed by quenching does not incite decomposition of the compound, which is explained by high stoichiometry of the grown crystal. Energy gap value after storage at room temperature and after the annealing is 1.65 eV, which corresponds with the data for monoclinic GaTe. The Vickers microhardness is 360 MPa.

A single-crystal sample of Gd2(MoO4)3 simultaneously doped with europium, terbium and thulium is grown. The Tm, Tb and Eu dopants are employed as the luminescent centers emitting light in the red, green and blue ranges. Spectroscopy investigation reveals that simultaneous luminescence of the centers of all three types to produce white light occurs only under the sample excitation with ultraviolet (UV) light within the wavelength range 350

Cadmium zinc telluride crystals were grown using the traveling heater method (THM) under microgravity conditions on board of Foton-M4 spacecraft, and a reference crystal was grown on Earth under gravity conditions. Structure, chemical and phase compositions of these crystals, their optical characteristics and microhardness were compared. It can be concluded that the THM growth in microgravity has a positive effect on CZT crystals, since they have more homogeneous composition and their structural perfection is improved as compared with the crystals grown under terrestrial conditions, which results in improvement of electric and optical characteristics.

New ZnSe ceramic material doped with Te is fabricated by nanopowder technology using cold compaction. It is found that phase composition, Te concentration and grain size of the nanopowders produced by direct deposition from vapor depend on temperature in a deposition zone. The higher the temperature, the greater is the fraction of stable cubic phase, the higher Te content, the greater grain size. It is shown that annealing of the ceramics brings to phase transition from wurtzite to sphalerite and dissolution of Te in ZnSe(Te) solid solution. Experimental data on the nanopowders and ceramic materials show that intensity of photoluminescence increases with increase in Te concentration in ZnSe(Te) cubic phase.

A1. Crystal structure A1. Defects A1. Dendrites A2. Growth from melt A2. Single crystal growth B1. Gallium monotelluride abstract GaTe crystals of 20 mm in diameter and up to 70 mm in length have been grown from melt using the high-pressure vertical zone melting (HPVZM) method. Real defect structure has been evaluated by XRD, SEM, EPMA, optical microscopy, microhardness and transparency measurements. The phase transfor- mation of hexagonal GaTe single crystal to monoclinic form by grinding has been detected. Such local defects as dendrites and dendrite clusters have been found at cleaved surface (0001), basal dislocations with density of 2 � 10

Bi 2 Se 3 /Ag, Cu x Bi 2 Se 3 /Ag heterojunctions have been obtained in which the bipolar resistive switching effect has been observed and studied for the first time. The carrier type was determined by the switching voltage polarity. During resistive switching the conductivity of the metastable “On” and “Off” states changes from metallic to non-metallic (activation).

ZnSe ceramic material doped with Te was produced at room temperature via compaction of nanocrystalline powders. Phase composition and microstructure were investigated and the effect of compression and heat treatment on phase transformations and grain growth was studied. Two ways of transition from metastable hexagonal to stable cubic phase were found. Two-staged annealing at Т=700 °С, 2 h followed by annealing at Т=800 °С, 2 h brings to complete transformation from wutzite to sphalerite phase. However, under these conditions some additive is lost during the heat treatment. Annealing of the compacted material at Т=800 °С, 2 h, its slow cooling to room temperature causes transformation into two sphalerite lattices with the unit cell parameters a1=5.660 A and a2=5.686 A, which transform during holding at room temperature into one sphalerite lattice with aZnSe(Te)=5.681±0.003 A. This heat treatment provides formation of the stable cubic state of the solid solution containing 2.5 wt% Te in ZnSe(1−x)Tex.

Microhardness of GaSe layered single crystals was studied. The dependences of Vickers microhardness on load and time under load were studied experimentally to find a range of these parameters acceptable for reliable measurements. A range of loads was found, where time under load had no significant effect on microhardness. Mechanisms of deformation under concentrated load are discussed. The GaSe crystals showed anisotropy of microhardness in the (0 0 0 1) plane; the coefficient of anisotropy is k=Hmax/Hmin=1.4. Profiles of indentations and topography of the surface in the vicinity of an indentation were studied by atomic force microscopy (AFM). The experiment demonstrated good agreement between the calculated and the measured depths of indentation pits. AFM proved to be an informative technique for the description of a structure of the material after microindentation. Basal and non-basal dislocations were studied by optical microscopy and AFM.

GaSe crystals have been grown from melt. There are several reasons why it is difficult to meet ideal demands for nonlinear optic material, GaSe single crystal. First, these crystals have a tendency towards lamination because of great difference in a and c crystal lattice parameters and very weak Vander der Waals forces in c direction. Next, there is a great difference in saturation vapor pressure of the components, which can cause nonstoichiometry of a melt-grown crystal composition. Another obstacle in the growth of perfect GaSe crystals is dendrite formation caused by instability of the growth front. To overcome this obstacle we used Bridgman technique and have found the temperature and pressure conditions, and growth velocity which provide growth of perfect bulk single crystals of about 100 mm in length and 20 mm in diameter. Sharp Laue patterns and a rocking curve confirm perfect structure of the grown crystals. Electron-probe X-ray microanalysis shows stoichiometric composition of GaSe crystals and X-ray phase analysis reveals presence of single-phased hexagonal structure.

Bulk specimens of highly dense CdTe ceramics were fabricated through compaction of vapor-deposited nanopowder. The microstructure, texture and other physical properties of the compacted CdTe were studied. The specimens were found to consist of grains of a certain crystallographic orientation. A two-component texture composed of 〈2 2 0〉 axial and {0 0 1}〈 h k 0〉 components was observed. The experimental results give evidence that dynamic recrystallization occurs under compressive stress in the temperature range from 20 to 200 °C. The ceramic specimens show extremely high-specific electrical resistivity on the order of 10 10 Ω cm. Their mechanical hardness is 1450 MPa, which is more that three times higher than the corresponding value of melt-grown CdTe. The compacted CdTe has rather high transmission in the wavelength range of 6–25 μm. These properties make this material interesting for the fabrication of infrared optical elements and for potential use as ionizing-radiation detectors.

We present inelastic neutron scattering data on optimally doped Tl2Ba2CuO6+δ (T c =92 K ), a single-layer copper oxide with undistorted copper oxide planes. The data indicate a magnetic resonant mode below Tc, as previously observed in YBa2Cu3O6+δ and Bi2Sr2CaCu2O8+δ. The mode is thus a generic feature of the copper oxide superconductors.

Superconducting at 40 K MgB2 -samples were obtained by direct reaction from elements in molybdenum crucibles under argon pressure. Pressure allows to provide annealing at temperature up to 1400oC, that resulting in rise of Tc and compactness of the ceramics, suggesting that there is a homogeneity range of composition for the compound., 5 pages, 5 figures, http://www.sttic.com.ru

We report on resistive measurements of the critical temperature of Tl 2 Ba 2 CuO 6+ x single crystals with x ≈0 (“optimally doped”, T c =89 K) and x >0 (“overdoped”, T c =40 K) under the applied quasihydrostatic pressure up to 1.1 GPa. The pressure has been found to shift T c upwards for the optimally doped sample and downwards for the overdoped one. We discuss the reasons leading to the change of the sign of d T c /d P upon overdoping, and the ramifications of our data for the existing models put forward to explain the influence of oxygen doping and pressure on T c .

Vertical high-pressure Bridgman (VHPB) Cd 1- x Zn x Te (0.04 x 241 Am radioactive source was found. Electron lifetimes below 1 μs were measured in crystals having significant numbers of micro-defects, compared to lifetimes of 5–15 μs found in spectrometer grade materials produced in the US. Furthermore, the zinc composition along the growth axis showed better homogeneity in comparison with the US material.

Solidification of melts at substantial supercooling is associated with instability on the growth front. This causes growth of dendrites, which form as a branched tree in a crystal. In the layered melt-grown GaSe crystals dendrites are observed, if growth rates are rather high [N.N. Kolesnikov, E.B. Borisenko, D.N. Borisenko, V.K. Gartman, Influence of growth conditions on microstructure and properties of GaSe crystals, J. Crystal Growth 300 (2) (2007) 294–298]. Models based on solution of the thermal diffusion problem are traditionally used to describe dendrite growth. Solution of this problem requires information about several physical parameters, such as diffusion coefficient, heat conductivity coefficient and supercooling at the solid/liquid interface. The study of scale invariance of dendrites formed in a crystal provides a new approach to solution of the dynamic growth problem. The calculated fractal dimensionality of the experimentally observed dendrites in GaSe crystals is D =1.7. It coincides with dimensionality of the clusters obtained through computer simulation in terms of the model of diffusion-limited aggregation (DLA). This result provides a new approach to description of the dynamics of dendrite growth. We have shown that the dendrite growth mechanism in the layered semiconductor crystals can be described by a two-dimensional DLA model. It is shown that probabilistic simulation can be used to show the development of a dendrite in any material. In contrast to the classical theories of dendrite growth, this approach does not require information on physical parameters.

We describe the current state of nuclear radiation detectors produced from single crystals of Cd1−xZnxTe(CZT), with 0.04

Single crystals of p-type semi-insulating Cd1 − xZnxTe (CZT) with x = 0.2, 0.3 and 0.4 were grown using the high-pressure vertical Bridgman method. The crystals showed a high degree of axial homogeneity over most of the length of the ingot. The crystals were characterized by measuring the specific resistivity, X-ray spectral analysis, triaxial rocking curves, photoluminescence, etch-pit density and photocurrent kinetics. Despite the high homogeneity the photocurrent kinetics are worse than n-type CZT (x = 0.1 and 0.2) also grown by high-pressure vertical Bridgman.

The high temperature superconductors Tl2Ba2CuO6+δ (Tl-2201) and Tl2Ba2Cu3O10 (Tl-2223) with one and three CuO2 planes were investigated by Raman scattering in order to see whether the electronic Raman scattering cross-section depends on the number of CuO2 planes, i.e. sheets of the Fermi surface. We present measurements of polarized Raman spectra in different scattering geometries on two single crystals of Tl-2201 (Tc = 90 K, 80 K), and one single crystal of Tl-2223 (Tc = 118 K), for temperatures below and above Tc. In B1g-symmetry the peak in the electronic Raman scattering is found at 460 cm−1 (Tc = 90 K), or 430 cm−1 (Tc = 80 K) for Tl-2201 and at 610 cm−1 for Tl-2223. This corresponds to 2Δ/kBTc = 7.4 ± 0.4 for both compounds. The A1g- and B2g symmetry components show smaller values for the peak position and a decrease linear in ω of the scattering intensity towards lower frequencies. The B1g-component shows a decrease cubic in ω of the scattering intensity towards lower frequencies. The spectral features of Tl-2201 and Tl-2223 are found to be independent of the number of CuO2-planes, i.e. of specific details of the Fermi surface. These observations are similar to the measurements on over- and underdoped Bi2Sr2CaCu2O8+δ single crystals. They are consistent with a dx2−y2-wave pairing mechanism, based on the theoretical model of Devereaux and Einzel.

The CdTe monodisperse nanoparticles and quasi-one-dimensional nanocrystals were obtained by the vapor deposition method. Transmission electron microscopy and X-ray powder diffraction were used to characterize these nanocrystals. It was found that nanocrystals had wurtzite or sphalerite structure depending on the growth conditions.

The crystal structure of a tetragonal single crystal of Tl-2201 with Tc = 30 K has been determined by the X-ray diffraction technique (a = 3.8717(3), c = 23.224(3) A, space group I4/mmm, Z = 2). The chemical composition is found to be Tl1.90(1)Cu.0.10(1)Ba2CuO6.18(4). Displacements of Tl and O3 atoms from their symmetric sites have been observed. Structural parameters of Tl-2201 cuprates with various Tc have been compared. The superconducting transition temperature is shown to correlate most strongly with the parameter c, with the length of the bond between Cu and apical oxygen as well as with the distance between Ba2+ and the cuprate plane.

Chemical vapour deposition (CVD) is applied to grow the multilayer structure on CdSe proposed as a promising coating for infra-red (IR) optics. The coating is composed of alternately grown CdS and CdSe single crystal layers. The proposed coating characteristics are expected to be much better than those of the coatings produced by the sputtering method.

Devices for experimental determination of surface tension and viscosity of A 2 B 6 compound melts have been developed. Surface tension, visocisity and volume effect of crystallization of melts of a few A 2 B 6 compounds have been determined. These properties are important for practice of A 2 B 6 single crystal growth from the melt.

A number of Tl 2 Ba 2 CuO x single crystals with different T c s from 32 to 115 K have been investigated by means of 205 Tl NMR in order to elucidate the possible role of electron spin fluctuations in high- T c superconductivity. In the normal state, the spin part of the Knight shift, K S , has been found to be temperature independent whereas the relaxation time, T 1 obeys T 1 T = a + bT with a increasing and b decreasing as T c is lowered. As in other HTCSs a gap between values of T 1 and K S points to the presence of strong antiferromagnetic correlations. With lowering temperature, T 1 T reaches a minimum value, which is nearly the same for all crystals, at temperatures 1.3 to 1.5 times higher than T c . Below the superconducting transition, in crystals with T c ⩾100 K both K S and T 1 exhibit a gap-like behaviour with a typical Δ/T c ≈3. In crystals with lower T c s a residual K S ( T →0) has been found which is most likely related to nuclei lying inside vortex cores.

Single crystals of 2201 phase with various superconducting transition temperatures ranging from nonsuperconducting to 110K have been obtained. An X-ray structural study of tetragonal single crystals with T c = 110 K, space group 14/mmm, a = 3.8686(3), c = 23.259(3) A, has been carreid out. We have found that thallium atoms are partially replaced by copper atoms. We have also found that Tl atoms and O(3) atoms linked with Tl are displaced from their symmetrical sites. A correlation between the structure and properties of Tl-2201 cuprate crystals has been established on the basis of our data and the data reported in the literature.

A method for visualization of the magnetic flux penetration and trapping in high-temperature superconductors (HTSC) using magneto-uniaxial ferrimagnetic films is described. The difference in the character of these processes in a number of materials (HTSC single crystals, films and ceramics) is studied. Specific features of remagnetization of Tl 2 Ba 2 CaCu 2 O x and YBa 2 Cu 3 O 7−δ single crystals in the superconducting state which do not fit the simple Bean model are found. Temperature dependences of the local magnetic susceptibility are measured in different sites of the samples. Non-uniformities of their superconducting properties related to structural defects are revealed.

Temperature and angular dependences of 205Tl line width, Δ 1 2 , and transverse relaxation time, τ, have been measured in two crystals of Tl2Ba2CuOx with Tc = 32 and 115 K, respectively. In the normal state both Δ 1 2 and τ have been found to be temperature-independent and not to vary with varying Tc, implying that the size of inhomogeneous broadening is also invariable. Analysis of the line width angular dependence shows that the inhomogeneous broadening originates, most probably, from local distortions associated with Cu substitution for Tl. A conclusion is that variations in Tc are not related to this substitution.

Tunneling junctions of the point-contact type of Bi 2 Sr 2 CaCu 2 O 8 single crystals have been studied, a natural oxide of aluminium electrode serving as a tunneling barrier. The ratio 2Δ/ kT c =5–6 was obtained in this investigation. A phenomenological model was applied for describing the behaviour of tunneling characteristics. From the numerical calculations and on the basis of this model, the phonon singularities in tunneling characteristics were treated by the standard program for the solutions of the Eliashberg equations and the electron-phonon interaction function, α 2 ( ω ) F ( ω ), was found.

A new approach for determination of dHc2/dT in vicinity of Tc has been suggested. Derivatives of critical fields on temperature have been found from measurements of magnetization of Tl2Ba2CuO6+x single crystals with various Tc.

Using 205 Tl NMR, the changes in electronic properties in the normal and superconducting state of the Tl 2 Ba 2 CuO 6+x compound associated with variation of T c , are studied in samples with T c =30, 100, and 115K. Decreasing T c with oxygen doping is shown to be associated with the growth of the static electron spin susceptibility and with lowering the Δ / T c ratio (Δ is superconductinh gap). This effect indicates to the corresponding weakening of coupling regime.

Photoluminescence and electronic resonance Raman scattering studies on overdoped Tl 2 Ba 2 CuO 6 with T c ∼ 85 and 30 K are reported. Luminescence is shown to be the primary contributor to secondary emission in these materials. A “2Δ-like” feature at ∼6 κT c for 85 K SC, and at ∼ 3.5 κT c for 30 K SC, is observed below T c .

Experiments are described on the determination of the spontaneous fission probability for the isotopes of elements 103, 105 and 107 produced by bombarding Tl, Pb and Bi targets with 50Ti, 51V, 54Cr, 55Mn and 58Fe ions. The upper limit of the spontaneous fission probability is established to be 2% for the isotopes 252, 253103. A new isotope of element 105 with mass number 257(T12 = 5 s) has been produced. In bombardment of 209Bi with 54Cr ions a new spontaneous fission activity with T12 ≈ 1–2 ms has been observed. The experimental data permit identification of this activity as the isotope of the new element 107 with mass number 261, which mainly undergoes α-decay (≈ 80%) resulting in the formation of the isotope 257105. The values of the partial α-decay and spontaneous fission half-lives of the isotopes 257105 and 261107 are compared with the systematics of the properties of transfermium nuclei.

The crsytal structure of single of the 1212 phase in the system Ti Ba Ca Cu O has been determined: a =3.8472 (5), c =12.721 (3) A, sp. gr. P4/mmm . The chemical formula of this phase has been refined: TiBa 2 (Ca 0.87 Ti 0.12 )Cu 2 O 7 , T c =80K, Meissner effect is 75–80%.