Superconductor-Semiconductor Metamaterial Photonic Crystals

We constructed theoretically one-dimensional photonic crystal (1DPC) by using a semiconductor metamaterial in the near-infrared range(NIR) which is composed of Al-doped Z n O(A Z O) and Z n O. The construction of this photonic crystal (PC) is based on a high-temperature superconductor material with the semiconductor metamaterial as constituent layers for this PC. The electromagnetic interactions with this periodic structure are investigated using the transfer matrix method (TMM) in the NIR range. The investigation shows that the reflectance spectra are depending on some parameters of the periodic structure such as the thicknesses of the constituent layers, temperature, and the angle of incidence.     

Optical Properties of Copper-Doped Lithium Niobate Crystals

We have studied the optical properties of copper-doped lithium niobate crystals using semiconductor light-emitting diodes and lasers emitting in the visible and ultraviolet spectral regions as excitation sources. The results demonstrate that, at an excitation frequency approaching the frequency of electronic absorption in copper ions, there is discrete resonance Raman scattering in the form of a frequency comb. The observed Raman satellites of discrete light scattering are due to polar longitudinal A₁ optical modes of the lithium niobate single crystal. Under excitation by a light-emitting diode with a wavelength of 520 nm, we observe a sharp increase in discrete light scattering intensity in comparison with the photoluminescence excited by shorter wavelength excitation sources.     

Investigation of Reflectance Properties in 1D Ternary Annular Photonic Crystal Containing Semiconductor and High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Bold">c</Emphasis></Subscript> Superconductor

In this paper, we present the theoretical investigation and study of reflectance properties in a 1D ternary annular photonic crystal (TAPC) containing a semiconductor and a high-temperature superconductor. The proposed structure consists of alternate layers of indium nitride (InN), Bi₂Sr₂CaCu₃O₈ (BSCCO), and air placed in free space. A reflectance spectrum of the TAPC is obtained by employing the transfer matrix method (TMM) in the cylindrical waves for both transverse electric (TE) and transverse magnetic (TM) polarized waves. From the study of reflectance spectra, it is observed that the reflection band of the annular photonic crystal depends on the azimuthal mode number m in addition to other parameters. It is found that for azimuthal mode number m = 0, the width of the reflection band of the annular photonic crystal is the same as that of a planar photonic crystal (PPC). When the azimuthal mode number increases, the width of the reflection band increases at higher m values (m >5) for TE waves. In the case of the TM wave, it is interesting to observe that a superpolariton gap is created for a higher value of the azimuthal number (m >0). Further, we see the effect of the starting radius (ρ ₀) on the reflection band of the TAPC structure at the given m number for both TE- and TM-polarized waves. Finally, the effect of temperature on the reflectance spectra for both TE and TM waves at the given ρ ₀ and azimuthal mode has been studied.     

Crystal Structure of Monohydrate of γ-Modification of Rubidium Uranoniobate

The compound γ-RbNbUO₆·H₂O was prepared for the first time as single crystals, which were studied by X-ray diffraction. Crystal data: rhombic system, space group Pcab, a = 7.614(2), b = 11.219(2), c = 16.510(3) Å, Z = 8. The crystal structure is built from uranium-containing layers of the composition [NbUO₆] _2∝ ^δ? , infinite in two directions. The water molecules and rubidium atoms distributed over two randomly occupied positions are accommodated between the layers.     

Crystal and molecular structures of tricarbonyltechnetium acetylacetonate and its adduct with diethylamine

The crystal and molecular structures of tricarbonyltechnetium acetylacetonate and its adduct with diethylamine were studied by single crystal X-ray diffraction. Tricarbonyltechnetium acetylacetonate crystallizes in the triclinic system, space group \(P\bar 1\), a = 8.1154(1), b = 8.1961(2), c = 8.2695(1) Å, α = 64.5618(9)°, β = 69.7899(8)°, γ = 83.6925(9)°, V = 465.652(14) ų (at 100 K); Z = 2. The adduct also crystallizes in the triclinic system, space group P{ie145-2}, a = 7.9338(3), b = 8.5421(3), c = 12.1506(7) Å, α = 96.961(3)°, β = 99.952(3)°, γ = 112.001(2)°, V = 736.25(6) ų (at 100 K); Z = 2. Tricarbonyltechnetium acetylacetonate has a centrosymmetrical dimeric structure. The dimerization occurs through the formation of a bridging bond with the methine carbon atom of the acetylacetonate ligand which is thus coordinated in the tridentate chelating-bridging fashion. The adduct has a monomeric structure with chelating coordination of the acetylacetonate ligand and coordination of diethylamine to the technetium atom via N atom. In both complexes, the carbonyl groups are in the fac position. Differences between the structures of tricarbonyltechnetium acetylacetonate in the crystal and in solution are discussed.     

Influence of Point Defects on the Electrical Conductivity and Dielectric Properties of Langasite

The temperature-dependent electrical conductivity and dielectric permittivity and room-temperature optical absorption spectra of La₃Ga₅SiO₁₄ (langasite) crystals grown under different conditions are measured. The resistivity and peak-loss temperature t _tanδ of the crystals are shown to be determined by the concentration of oxygen vacancies, which originate from changes in melt composition during crystal growth. The t _tanδ of langasite is shown for the first time to be anisotropic (measurements on Z- and X-cuts). The properties of the crystals are suitable for the fabrication of stable piezoelectric elements capable of operating above 600°C.     

X-ray analysis of 2-aniline benzo(2,3-<Emphasis Type="Italic">b</Emphasis>) cyclopentane-1,3-dione

The molecular and crystal structure of 2-aniline benzo(2,3-b) cyclopentane-1,3-dione has been determined by X-ray crystallographic techniques. This compound crystallizes in the orthorhombic space groupP2₁2₁2₁ with unit cell parameters:a = 5.467(1),b = 10.657(3),c = 19.602(6) Å;V = 1142.01(5) ų,Z = 4. The crystal structure has been resolved up to anR-factor 0.050 for 1129 reflections. All the three rings in the structure are planar. However, the dihedral angle between the phenyl ring and the moiety comprising of a five-membered and six-membered ring is 92.4°. The oxygen atom O1 acts as a trifurcated acceptor and is involved in the formation of three intermolecular interactions.     

Crystal and molecular structure of adducts of uranyl pivaloyltrifluoroacetonate with hexamethylphosphoramide and of uranyl trifluoroacetylacetonate with trimethyl phosphate

Crystal and molecular structures of adducts of uranyl pivaloyltrifluoroacetonate with hexamethylphosphoramide [UO₂(PTFA)₂(HMPA)] (I) and of uranyl trifluoroacetylacetonate with trimethyl phosphate [UO₂(TFA)₂(TMP)] (II) were determined. Compound I crystallizes in the monoclinic system, space group P2₁/n; a = 16.9384(3), b = 9.1090(2), c = 20.9844(4) Å, β = 101.5337(10)°, V = 3172.34(11) ų (at 100 K); Z = 4. Compound II crystallizes in the rhombic system, space group Pbca; a = 17.8214(4), b = 7.7786(2), c = 30.9176(7) Å, V = 4285.97(18) ų (at 100 K); Z = 8. In both cases, the cis isomer in which the neutral ligand is located between the trifluoromethyl groups is realized. Compound I differing from II by the stronger branching of ligand periphery is characterized by stronger structural deformations in the crystal.     

Crystal structures of Ln<Subscript>2</Subscript>TiO<Subscript>5</Subscript> (Ln = Gd,Dy) polymorphs

Single crystals of four Ln₂TiO₅ polymorphs have been grown, and their structures have been determined: orthorhombic (Gd₂TiO₅, a = 10.460(5), b = 11.317(6), c = 3.750(3) Å, Pnam, Z = 4), hexagonal (Gd_1.8Lu_0.2TiO₅, a = 3.663(3), c = 11.98(1) Å, P6₃/mmc, Z = 1.2), cubic (Dy₂TiO₅, a = 10.28(1) Å, Fd3m, Z = 10.4), and monoclinic (Dy₂TiO₅, a = 10.33(1), b = 3.653(5), c = 7.306(6) Å, β = 90.00(7)°, B2/m, Z = 2.4). The last polymorph has been identified for the first time.     

Synthesis and structure of the CsSmP<Subscript>4</Subscript>O<Subscript>12</Subscript> cyclotetraphosphate (cubic CsNdP<Subscript>4</Subscript>O<Subscript>12</Subscript> structure)

CsSmP₄O₁₂ crystals have been prepared at 300°C in molten polyphosphoric acids containing Cs, Mg, and Sm cations, and their crystal structure has been determined: sp. gr. I \(\bar 4\) 3d, a = 15.1225(8) Å, Z = 12, CsNdP₄O₁₂ structure.     

Crystal structure of the low-temperature forms of cesium and rubidium orthophosphates

The crystal structure of the low-temperature forms of the Cs₃PO₄ and Rb₃PO₄ orthophosphates has been determined for the first time by neutron diffraction using the Rietveld method. Cs₃PO₄ and Rb₃PO₄ are shown to be isostructural with K₃PO₄: orthorhombic cell (sp. gr. Pnma, Z = 4); lattice parameters a = 1.23177(6) nm, b = 0.88948(4) nm, c = 0.64197(3) nm for Cs₃PO₄; a = 1.17362(2) nm, b = 0.81046(1) nm, c = 0.615167(9) nm for Rb₃PO₄.     

X-ray structure determination and analysis of hydrogen interactions in 3, 3′-dimethoxybiphenyl

The crystal structure of 3, 3′-dimethoxybiphenyl has been determined by X-ray diffraction methods with an aim of describing the hydrogen interaction in biphenyl derivatives. The title compound crystallizes in monoclinic space groupP2₁/c with unit cell dimensions,a = 7.706(1),b = 11.745(2),c = 12.721(2) Å, β = 92.31(1)°,Z = 4 and its structure has been refined up to the reliability index of 3.8%. The average torsion angle about the inter-ring C-C bond is 37.5°. The O1 and Ol′ atoms of the methoxy group are deviated by 0.046(1) Å and 0.234(1) Å from the mean planes of respective rings. The crystal cohesion is pronounced due to three-inter-molecular C-H...O hydrogen bonds.     

Synthesis and microwave dielectric properties of Zn<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>Nb<Subscript>2</Subscript>O<Subscript>6+<Emphasis Type="Italic">x</Emphasis></Subscript>

We have studied the formation of zinc niobate, ZnNb₂O₆, with the columbite structure and the microstructure and microwave dielectric properties of Zn_1+x Nb₂O_6+x ceramics. The results demonstrate that, in the range 0.005 ≤ x ≤ 0.03, the excess zinc reduces the porosity of the material and increases its microwave quality factor Q. For x ≥ 0.03, the Q of the ceramics decreases because of the formation of an additional, zinc-enriched phase. Sintering in an oxygen atmosphere is shown to improve the dielectric properties of stoichiometric ZnNb₂O₆.     

Crystal and molecular structure of uranyl acetylacetonate dimer, [UO<Subscript>2</Subscript>(C<Subscript>5</Subscript>H<Subscript>7</Subscript>O<Subscript>2</Subscript>)<Subscript>2</Subscript>]<Subscript>2</Subscript>

The crystal and molecular structure of uranyl acetylacetonate dimer was determined by single crystal X-ray diffraction. The compound crystallizes in the tetragonal system, a = 7.9420(2), c = 40.1240(13) Å (at 100 K), Z = 4, space group P4₁2₁2. Dimeric uranyl acetylacetonate molecules in the crystal are formed by bridging bonding of one of O atoms of the acetylacetonate ligands with U atoms, so that the coordination polyhedra of U atoms (distorted pentagonal bipyramids) share a common equatorial edge. The dimer has a nonplanar structure, being significantly bent along the conventional line connecting the bridging O atoms.     

Fabrication of quasi-superlattices at the interface between 3C-SiC epitaxial layer and substrates of hexagonal SiC polytypes by sublimation epitaxy in vacuum

Transmission electron microscopy has been used to study the structure of a transition layer between a hexagonal substrate (6H-SiC and 4H-SiC) and a cubic silicon carbide layer grown by sublimation epitaxy in vacuum. It is shown by microdiffraction analysis that the transition layer with a thickness of 210 nm is constituted by alternating layers of cubic (3C) and hexagonal (6H) silicon carbide. It is demonstrated that 6H-SiC/3C-SiC and 4H-SiC/3C-SiC quasi-superlattices can be produced by this method.     

High-temperature crystal chemistry of Na<Subscript>6</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>

Thermal deformations of Na₆(UO₂)₂O(MoO₄)₄ were studied by high-temperature powder X-ray diffraction. The compound crystallizes in the triclinic system, space group Р\(\bar 1\), a = 7.636(7), b = 8.163(6), c = 8.746(4) Å, α = 72.32(9)°, β = 79.36(4)°, γ = 65.79(5)°, V = 472.74(4) ų. It is stable in the temperature interval 20–700°С. The thermal expansion coefficients (TECs) are α₁₁ = 25.5 × 10^–6, α₂₂ = 7.8 × 10^–6, and α₃₃ = 1.1 × 10^–6 (°C)^–1. The orientation of the TEC pattern relative to the crystallographic axes is a₃₃^Z = 45°, a₃₃^X = 122°, a₂₂^Z = 59°, and a₂₂^X = 66°. The anisotropy of the thermal expansion is due to specific features of the crystal structure of the compound.     

Properties of fluorine-doped PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> ceramics

We report the first fluorine doping of lead magnesium niobate in the PbMg _{(1 + x)/3}Nb_{(2 ? x)/3}O_{3 ? x} F _x system in a wide composition range, x = 0.025 to 0.625. The fluorine content of the samples is shown to be substantially lower than the intended one because of the fluorine volatilization in the form of HF during synthesis and sintering in air. The ceramics consist of magnesium and lead oxides undetectable by x-ray diffraction, and a perovskite phase whose composition can be represented by the formula PbMg_{(1 + m)/3}Nb_{(2 ? m)/3}O_{3 ? m} F _m , where the fluorine content after sintering is m ≤ 0.12. The PbO and MgO contents of the ceramics depend on the starting mixture composition (x) and heat-treatment conditions (hydrogen fluoride and lead oxide volatilization). As a result of the low fluorine content, the diffraction patterns of the samples show no superlattice reflections, and their lattice parameter varies insignificantly with x. Data are presented on the temperaturedependent dielectric permittivity of ceramic samples sintered and annealed under different conditions.     

Synthesis,Crystal Structure,Vibrational and Magnetic Properties of a New Organic–inorganic Hybrid Material: 2-Amonium-methyl-1-Ethylpyrrolidinium Tetrachlorocuprate (II)

Synthesis, crystal structure, vibrational study and magnetic properties of the compound (C₇H₁₈N₂) CuCl₄ are reported. The latter crystallizes in the monoclinic system (space group P2 ₁, Z = 4) with the following unit cell dimensions: a = 7.569(5) Å b = 14.174(5) Å, c = 13.193(2) Å and β = 105.53(3)^°. Besides, its structure was solved using 5754 independent reflections down to R = 0.0475. The atomic arrangement can be described by alternating organic and inorganic layers stacked in the [\(\bar {1}\)01] direction, made up of tetrahedral of tetrachlorocuprate CuCl\(_{4}^{2-}\) sandwiched between two organic layers. In crystal structure, the inorganic layer, built up by independent monomeric [CuCl₄]^2?, is connected to the organic ones through hydrogen bonding in order to build a three-dimensional network. The magnetic behavior of (C₇H₁₈N₂) CuCl₄ samples was investigated as a function of temperature and applied field. At hightemperature paramagnetic behavior, and at low temperature, evidence for weak ferromagnetism, reinforced by a hysteresis loop at 2 K is observed. The magnetic behavior of (C₇H₁₈N₂) CuCl₄ is attributed to Cu (II) due to the presence of an active Jahn–Teller effect in the d ⁹ electronic system, which give rise to short-range weak ferromagnetism.     

Quantum Gas of Polar Molecules Ensembles at Ultralow Temperatures: <Emphasis Type="Italic">f</Emphasis>-wave Superfluids

We investigate novel f-wave superfluids of fermionic polar molecules in a two-dimensional bilayer system with dipole moments polarized perpendicular to the layers and in opposite directions in different layers. The solution of the BCS gap equation reveals that these unconventional superfluids emerge at temperatures on the level of femtokelvin which opens up new possibilities to explore the topological \(f+i f\) phase, quantum interferometry and Majorana fermions in experiments with ultracold polar molecules. The experimental realization of such interesting novel f-wave pairings is discussed.     

Hybrid Josephson Junctions with Iron-based and Conventional Superconductor Electrodes

We investigate the iron-based superconductor Ba(Fe _1?x Co _x ) ₂As ₂ (Ba-122) regarding its superconducting properties and possible applications. Therefore, Ba-122 thin films are used as base electrode to prepare different kinds of hybrid Josephson junctions with a counter electrode of the conventional superconductor Pb. Additionally, we use both c-axis and a b-plane transport geometries and different kinds of barriers like interface-engineered surfaces, sputtered titanium oxide and gold layers. Temperature dependent I– V characteristics as well as magnetic field dependence and microwave response of the junctions are shown. The examined I– V characteristics and I _c R _n– T behaviours of each junction type are compared and described according to the electrical behaviour of the respective normal conducting or insulating barrier. While the I _c R _n product of the interface-engineered barrier junction was 12 μV and the planar junction with Au barrier showed 18 μV, we could increase the I _c R _n to 90 μV for planar TiO _x barrier junctions.