Structural reasons for the nonlinear optical properties of KTi<Subscript>0.96</Subscript>Zr<Subscript>0.04</Subscript>OPO<Subscript>4</Subscript> single crystals

This paper reports on the results of the precision X-ray structural investigations of KTi_0.96Zr_0.04OPO₄ single crystals at room temperature. It is established that the incorporation of zirconium atoms into the structure of KTiOPO₄ (KTP) crystals does not lead to substantial changes in the framework structure and results only in an insignificant decrease in the scatter of the distances in the PO₄ tetrahedra and the formation of more symmetric (TiZr)O₆ octahedra as compared to the TiO₆ octahedra. However, the incorporation of zirconium atoms into the KTP structure is accompanied by the redistribution of the electron density in the crystal as a whole, so that the electron density increases in the region of the positions occupied by the potassium atoms. This changes the nonlinear optical properties of the given series of crystals, which are estimated from the intensity of the second harmonic generation signals.     

Characterization of Vacuum Evaporated Polycrystalline Cd0.96Zn0.04Te Thin Films by XRD,Raman Scattering and Spectroscopic Ellipsometry

Cd_0.96Zn_0.04Te thin films are deposited onto well cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation and the films are annealed at 423 K. Rutherford Backscattering Spectrometry and X‐ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the as‐deposited films is 3.7 nm and on annealing the films at 423K, the rms roughness value decreases to 3.4 nm. The Raman spectra of the Cd_0.96Zn_0.04Te films are recorded at room temperature to study lattice vibrations and their interactions with other excitations. The intensity of the peak increases and the FWHM decreases on annealing the films. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E), of polycrystalline Cd_0.96Zn_0.04Te thin films in the 1.3 ‐ 5.5eV photon energy range at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points are due to interband transitions.     

Optical and opto‐electronic properties of polycrystalline Cd0.96Zn0.04Te thin films

Cd_0.96Zn_0.04Te thin films are deposited onto thoroughly cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films are found to have good stoichiometry as analyzed by Rutherford Backscattering Spectrometry. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the films evaluated by AFM is 3.7 nm. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E) at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+ Δ₁ and E₂ critical points. The band gap energy of the films measured by optical transmittance measurement is 1.523 eV. The PL spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and deeper impurity levels. The PL line shapes give indications of the high quality of the layers.     

Structural Characterization of Na<Subscript>0.96</Subscript>Ho<Subscript>9.04</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>6</Subscript>Cl<Subscript>0.02</Subscript>O<Subscript>1.98</Subscript> Apatite Prepared by Mechanical Milling

Abstract  

In this paper we report the synthesis and structural characterization of Na_0.96Ho_9.04(SiO₄)₆Cl_0.02O_1.98 apatite prepared by mechanical milling at room temperature, in which well crystallized sample was obtained after heating the sample at 1123 K. The crystal structure study was carried out by synchrotron radiation diffraction. This apatite crystallizes in the hexagonal space group P6 ₃ /m (No. 176) with cell parameters a = 9.3444(1) ?, c = 6.7611(1) ?, unit cell volume of 511.27(1) ?³ and Z = 1. As in other rare-earth orthosilicate apatites, it was found that sodium cations are mixed with holmium occupying the 4f position at the center of tricapped trigonal prisms; while holmium fully occupies the 6h position at the center of a seven-coordinated polyhedron. No vacancies are present in the two crystallographic sites available for holmium atoms. The chemical composition was established by wavelength dispersive spectroscopy.     

Crystal structure of potassium titanyl phosphate doped with zirconium

This paper reports on the results of precision X-ray structural investigations of single crystals of the compounds KTi_0.96Zr_0.04OPO₄ (at 293 K) and KTi_0.97Zr_0.03OPO₄ (at 293 and 105 K). No significant splitting of the positions occupied by potassium atoms is revealed. This result is in agreement with a considerable decrease in the electrical conductivity of potassium titanyl phosphate KTiOPO₄ (KTP) crystals doped with zirconium (KTP: Zr) as compared to crystals of undoped potassium titanyl phosphate. It is established that the difference between the Ti-O bond lengths in chains formed by titanium octahedra is not a single structural parameter responsible for the nonlinear optical properties of crystals in this series.     

Refinement of composition and structure of holtite I

A new version of the structural formulas of holtite I, (Al_0.61Ta_0.25□)(Al_0.96□)₂(Al_0.96□)₂ × (Al_0.90□)₂(Si_2.49Sb_0.35As_0.13)O_13.46(O_0.48OH_0.52)(BO₃), is reported. The main changes in this formula are related to the incorporation of arsenic atoms in (Sb,As)O₃ pyramides into the structure.     

The 0.96(Bi0.5Na0.5)TiO3 – 0.04BaTiO3 crystal structure: A high‐Q,high‐counting statistics synchrotron diffraction analysis

A synchrotron powder diffraction experiment, especially designed to shed light on the controversial problem of the crystal structure of 0.96(Bi_0.5Na_0.5)TiO₃ – 0.04BaTiO₃, is reported. The investigated material is a key component of the current international search for lead‐free ferro‐piezoelectrics. A wide angular range diffraction pattern was measured in high resolution configuration, with emphasis on trustable counting stastistics in the high‐Q interval. Cc and R3c structural models were tried as primary phases. The obtained experimental results are incompatible with the monoclinic model and clearly favor the rhombohedral symmetry.     

Charge state and hydrogen diffusion in Ti-based alloys

The electronic structure, charge state, and hydrogen diffusion in icosahedral Ti-based alloys have been investigated by the methods based on the density-functional theory. The charge state of the hydrogen atom in Ti₃₆Zr₃₂Ni₁₃ has been determined for different types of tetrahedral voids. The charge state of hydrogen atoms in Ti₃₆Zr₃₂Ni₁₃, Ti₃₆Hf₃₂Ni₁₃, and Ti₄₈Zr₈Fe₁₈ is calculated for the ratio H/M = 1.7, where H is the number of hydrogen atoms and M is the number of metal atoms. It is established that hydrogen atoms in all objects studied are in an almost neutral state. The hydrogen diffusion coefficient is determined for Ti₃₆Zr₃₂Ni₁₃.     

Vibrational spectra of the YbB<Subscript>12</Subscript> Kondo insulator

The density of phonon states for the YbB₁₂ Kondo insulator is calculated from the inelastic neutron scattering spectra of this compound. It is established that thermal vibrations of rare-earth atoms predominantly occur in the low-energy range. These atoms are most weakly bound in the crystal structure of the YbB₁₂ Kondo insulator. The high-energy part of the vibrational spectrum is determined by thermal vibrations of the boron atoms forming a rigidly connected structure of the compound. It is revealed that the temperature dependence of the intensity of the phonon peak attributed to thermal vibrations of the ytterbium atoms exhibits an anomalous behavior. This circumstance suggests that the magnetoelastic coupling occurring in the structure of the YbB₁₂ Kondo insulator is relatively strong and can contribute to the magnetic excitation spectrum of this compound.     

Study of the chemical reactions' influence on semiconductor films structure formation by the Monte-Carlo method

The investigation by the Monte-Carlo method of the growth of the silicon epitaxial film at a chloride CVD system has allowed to find out the composition of adsorption layer, the micromechanism of the reactions of Si atoms building-in into the growing crystalline layer and the growth conditions influence on the growth rate and film surface roughness. The change of adsorptive layer composition in the system SiCl₄—HCl—H₂ (fraction of adaatoms, silicon atoms built-in a crystal and molecules SiCl₂) depending on temperature has been determined. The change of silicon film growth rate depending on temperature and concentration change of SiH₂Cl₂ has been established and the contribution of growth mechanism (with participation of adatom, silicon atoms and molecules SiCl₂) into the total rate of film growth has been shown.     

Influence of partial replacement of Cu by Cd and Zn atoms on polymorphous transformation in Cu<Subscript>1.75</Subscript>Te crystal

A layer Cu_{1.75 ? x}Te single crystal in which some Cu atoms were replaced by Cd and Zn atoms (x = 0.05) was studied by high-temperature X-ray diffractometry. It was established that this replacement substantially affects the number and temperature of polymorphous transformations.     

Crystal structure of Ga<Subscript>0.5</Subscript>In<Subscript>1.5</Subscript>Se<Subscript>3</Subscript> solid solution

A solid solution of the GaIn₃Se₆ (2Ga_0.5In_1.5Se₃) composition with a hexagonal lattice (a = 7.051(3) Å, c = 19.148(2) Å, sp. gr. P6₁, z = 6, V = 824.4332(4) ų, ρ = 5.379(2) g/cm³) has been synthesized as a result of alloying Ga, In, and Se elements with a metal ratio of 1: 3. It was established that six out of nine In atoms in the lattice are located in a trigonal bipyramid, while the other three In atoms and three Ga atoms have a tetrahedral coordination.     

Specific features of nonvalent interactions in orthorhombic perovskites

It is established that isostructural orthorhombic perovskites ABO₃ (sp. gr. Pnma in different systems, no. 62, Z = 4), depending on the specificity of nonvalent interactions (which determine the combinatorial-topological type of the Voronoi-Dirichlet polyhedra (VDPs) of four basis atoms), are divided into ten different stereotypes. It is shown by the example of 259 perovskites belonging to the DyCrO₃ stereotype that VDP characteristics can be used to quantitatively estimate the distortion of BO₆ octahedra, including that caused by the Jahn-Teller effect. It is found that one of the causes of the distortion of the coordination polyhedra of atoms in the structure of orthorhombic perovskites is heteroatomic metal-metal interactions, for which the interatomic distances are much shorter than the sum of the Slater radii of A and B atoms.     

Crystal Structure Study of Co(II) Complexes with 2,2′-(1,4-Ethylenedioxyl) Dibenzoic Acid-[Co · L · (H2O)3]n · nH2O· 0.2 nH2O

The structure ofS the title complex [Co. L. (H₂O)₃]_n. nH₂O. 0.2 nH₂O has been established by single crystal X-ray diffraction. Crystals of the complex are monoclinic, space group C2/c with cell constants α = 45.29(4), b=10.631(6), c = 8.015(6) Å, β = 90.65(8)°, Z = 8, D_c = 1.489 g. cm⁻³ The structure was solved and refined to R =0.0478 (wR = 0.0577). In the chain structure, Co(II) ions are hexacoordinated by 0 atoms in an octahedral arrangement. CoO₆ octahedra share corners (bridged) through O atoms of water, with each L^2--ligand binding two adjacent Co atoms.     

Gamma-resonance study of nanopowders with different dispersion and quasicrystalline phases in the Al-Cu-Fe system

⁵⁷Fe Mössbauer spectroscopy has been used to monitor synthesis of quasicrystals in the Al-Cu-Fe system and study the influence of the size of quasicrystalline particles in powder samples of the Al_63.1Cu_25.6Fe_11.3 alloy on the properties of synthesized materials. Quasicrystalline samples of different dispersion with particle sizes from 0.3 to 15 μm have been studied in the temperature range 80–295 K. It is established that iron atoms in an Al_63.1Cu_25.6Fe_11.3 quasicrystals occupy four types of structural positions, which differ in the atomic composition of the nearest environment. The results of the analysis suggest the dependence of the hyperfine-interaction parameters on the degree of sample dispersion. The components corresponding to iron atoms in both the surface layer and bulk of microparticles are isolated in the Mössbauer spectra. No magnetic hyperfine splitting has been found in the Mössbauer spectra in the entire temperature range. This fact suggests that a localized magnetic moment is absent in iron atoms.     

Crystal structure of the binary complex of cobalt and zinc chlorides with carbamide [Co(OCN<Subscript>2</Subscript>H<Subscript>4</Subscript>)<Subscript>5</Subscript>(H<Subscript>2</Subscript>O)][ZnCl<Subscript>4</Subscript>]

Mixed single crystals of [Co(OCN₂H₄)₅(H₂O)][ZnCl₄] were grown by the isothermal evaporation of an aqueous solution. The crystal structure of this complex was established by X-ray diffraction (R = 0.052 based on 7003 reflections). The crystals consist of [Co(OCN₂H₄)₅(H₂O)]²⁺ cations containing Co atoms in an octahedral coordination and [ZnCl₄]²⁻] anions containing Zn atoms in a tetrahedral coordination. The carbamide molecules are involved in both intramolecular and interionic hydrogen bonds. The H₂O molecule forms hydrogen bonds with the anions.     

Influence of doping on the microstructure and kinetic parameters of GaSb-FeGa1.3 eutectics

Electron microscopy and X-ray spectroscopy analysis of GaSb-FeGa_1.3 eutectic composite doped with tellurium atoms is performed. It is established that doping changes the GaSb-FeGa_1.3 eutectics microstructure; sizes, shape, and density of FeGa_1.3 metallic inclusions; and the interface regions between the matrix and inclusions. Influence of doping on the anisotropy of kinetic parameters is shown.     

Simulation of transport properties of α-AgI1 − x Clx(0 < x < 0.25) by the molecular dynamics method

The transport characteristics of the α-AgI_{1 ? x} Cl_x solid solutions have been calculated by the molecular dynamics method. It is established that the diffusion coefficient of cations decreases with an increase in the concentration of chlorine atoms, which agrees with the well-known experimental data on the behavior of ionic conductivity.     

Synthesis and crystal structure of new carbonate NaPb2(CO3)2(OH)

Crystals of a new lead carbonate, NaPb₂(CO₃)₂(OH), sp. gr. P31c, were prepared by hydrothermal synthesis. The crystal structure was established by the heavy-atom method without knowing the exact chemical formula of the compound. The polar structure of the carbonate and the distortion of the pseudosymmetry described by the supergroup P $\bar 3$ 1c are caused by the acentric arrangement of the oxygen atoms providing the satisfactory coordination of Pb and Na atoms. The bonds between a hydroxyl group and two crystallographically independent Pb atoms are directed along the c-axis and have different lengths. The study of the carbonate by the second harmonic generation method in a temperature range of 20–250°C revealed the nonlinear optical properties comparable with the similar properties of quartz. The comparison of the structure of the new carbonate with a number of carbonates demonstrated that the new compound is structurally similar to ewaldite BaCa(CO₃)₂, diorthosilicate NaBa₃[Si₂O₇](OH), and Ba[AlSiO₄]₂ containing a double silicon—oxygen layer.     

Atomic structure of Cd1 − x Zn x Te solid solution single crystals and structural prerequisites of their ferroelectricity

Precision X-ray structural investigation of Cd_{1 ? x} Zn _x Te single crystals (x = 0.04, 0.10, 0.21, 0.30, 0.40) is performed at temperatures below and above the ferroelectric phase transition. The regularities associated with the increase in the concentration of Zn atoms in solid solutions are revealed. It is established that the unit cell parameter of the crystals varies according to the Vegard law. The thermal parameters of Te and Zn atoms are strongly overestimated within the model of a sphalerite-type average structure. It is found that the positions of the Zn cations are split and the anion sublattice is disordered in such a way that the Te anions are predominantly displaced along the threefold axes. The Zn atoms can serve as off-center impurities. This phenomenon offers strong possibilities for manifesting the ferroelectric properties in the solid solutions under investigation.