Effect of the ultrasonic frequency on the multiple X-ray scattering from a LiNbO<Subscript>3</Subscript> crystal modulated by a surface acoustic wave

The effect of multiple scattering on the formation of the θ-2θ scan curves for a crystal modulated by a surface acoustic wave (SAW), depending on the ultrasonic frequency, has been investigated in the frame-work of the dynamical theory of X-ray diffraction. A model of a Rayleigh surface wave has been analyzed as applied to X-ray diffraction with allowance for the transverse and longitudinal elastic lattice strains. Using the example of the 127° Y′ cut of the LiNbO₃ crystal, it is established that the effects of multiple scattering can be neglected for ultrasonic frequencies above 650 MHz; this finding significantly simplifies the numerical calculations of X-ray diffraction from a crystal modulated by a short-wavelength SAW. A comparative quantitative analysis of the experimental data on synchrotron scattering from the 127° Y′ cut of a LiNbO₃ crystal modulated by a 952-MHz SAW have been performed, both taking into account and neglecting the effects of multiple scattering. It is shown that the computation time can be reduced by 2 to 3 orders of magnitude.     

Development of methods for ultrasonic scanning of X-ray wavelength

The method for X-ray wavelength tuning using an adaptive element (a quartz monolithic resonator modulated by a standing longitudinal low-frequency ultrasonic wave) has been proposed and implemented. This method is characterized by high tuning accuracy and possibility of scanning X-ray beam parameters with a time resolution of up to 3 μs.     

Resonance excitation of polaritons by bulk electromagnetic waves in the layered systems with anisotropic substrates

The possible resonance excitation of surface electromagnetic waves by the bulk waves at the interface between a positive transparent uniaxial crystal and an isotropic medium has been predicted. The existence of the surface waves is provided by anisotropy of one of the boundary media. The tensor relation between the vector amplitudes of an exciting bulk electromagnetic wave and the excited surface wave is established. The ratio of the moduli of the tangential components of these amplitudes is analyzed as a function of the angle of incidence and the polarization of the bulk wave. The numerical calculations are performed for the surface waves at the interface between paratellurite TeO₂ and a KRS-6 (TlBr 30%-TlCl 70%) crystal.     

Growth and scintillation properties of the Eu2W3O12 crystal

The growth and scintillation properties of the Eu₂W₃O₁₂ crystal are reported. The Eu₂W₃O₁₂ single crystal has been grown by the Bridgman method. And the colored Eu₂W₃O₁₂ single crystal has been achieved. The Ultraviolet fluorescence spectra and the X-ray excited luminescence spectra show that the Eu₂W₃O₁₂ crystal has emission at the 590 nm and 612 nm. The fluorescence decay time of the Eu₂W₃O₁₂ crystal is about 520 μs. The luminosity of the Eu₂W₃O₁₂ single crystal under X-ray excitation is about 8% of the luminosity of the BGO single crystal. Those results show that the Eu₂W₃O₁₂ crystal has potential application as the X-ray intensifier.     

Determination of the Surface Tilt Angle by Attenuated Total Reflection

Thin SiO₂ layers prepared by oxidizing an organo-silane in an Ar/O₂ rf plasma discharge produce parallel alignment for nematic liquid crystals with essentially zero tilt. In addition, if the rf plasma system is arranged to produce an Ar/O₂ beam, uniform parallel alignment can now be obtained with the director in the substrate plane at an angle perpendicular to the plane of incidence of the rf plasma beam. We have studied the aligning properties of such films using the evanescent wave generated by attenuated total reflection (ATR) on a thin gold film when a surface electromagnetic wave is excited. Liquid crystal cells were constructed on a high index glass prism with a 500 Å gold film and a 200 Å aligning layer. By following the ATR minimum as a function of applied electric field, the tilt at the interface of the liquid crystal and the aligning layer was calculated.     

Dynamic variation in the lattice parameter of a crystal under ultrasonic treatment in X-ray diffraction experiments

The X-ray diffraction in the Laue geometry is investigated in germanium and silicon single crystals upon excitation of long-wavelength ultrasonic elastic strain waves traveling along the sample surface. The X-ray diffraction beam is bounded by a slit 0.2 mm in size, which is considerably less than the wavelength of the ultrasonic wave. The use of this slit makes it possible to separate crystal regions with a nearly homogeneous strain. As a consequence, the rocking curves stroboscopically measured in a double-crystal dispersionless scheme at different instants of time almost coincide with those for a perfect crystal with a lattice parameter varying in time. The rocking curves measured in a time-integrated mode turn out to be broadened, but their integrated intensities remain unchanged. Possible applications of the developed method are discussed.     

The features of identifying lines in a diffraction image formed by a widely divergent X-ray beam

A method for identifying lines in a diffraction image formed by a widely divergent X-ray beam and a technique for measuring the crystal structure parameters in the case of asymmetric crystal position have been developed. It is established that, once the distances between a crystal and a photographic plate and between the points of intersection of the hyperbola branches in a diffraction image are known, one can determine the angle between the crystal’s zone axis and the wave vector, which leads to multiwave diffraction. Relations linking this angle with the parameters of two atomic planes are obtained. It is found that, to measure the parameters of atomic planes belonging to a given zone, one can use different sets of crossed hyperbolas formed by radiations K _α and K _β. The measurements and calculations performed for the same sample (Si crystal), mounted symmetrically and asymmetrically, confirm the reliability of the proposed method.     

Self-assembly of highly crystalline spherical BiVO4 in aqueous solutions

Spherical bismuth vanadate particles are self-assembled from aqueous Bi(NO₃)₃ and NH₄VO₃ solutions by adjusting pH and tuning the amount of surfactant sodium dodecyl sulfate (SDS) via facile hydrothermal method. The BiVO₄ samples were characterized by X-ray diffraction (XRD) and the peaks suited well with the pure phase monoclinic scheelite BiVO₄. Field emission scanning electron microscopy (SEM) showed the average size of the spherical particles was 5 μm and the assembling stages in the hydrothermal synthesis process were recorded. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) revealed the nanoparticles were single crystal. FT-IR spectroscopy test results demonstrated there was no SDS left in the samples. The mechanism of the self-assembling has also been proposed.     

Excitation of intense acoustic waves in hexagonal crystals

Resonant excitation of an intense elastic wave using reflection of a pump wave from a free surface of hexagonal crystal is described. A resonance arises in the case of specially chosen propagation geometry where the reflecting boundary slightly deviates from symmetric orientation and the propagation direction of an intense reflected wave is close to that of an exceptional bulk wave, which satisfies the free boundary condition in unperturbed symmetric orientation. It is shown that, in crystals with elastic moduli c ₄₄>c ₆₆, a resonance arises when the initial boundary is chosen parallel to the hexagonal axis 6, whereas in crystals characterized by the relation c ₄₄<c ₆₆ a resonance occurs when the initial boundary is orthogonal to this axis. The fraction of the pump energy transferred to the excited beam depends on the specific relations between the elastic moduli and can be rather significant for specially chosen crystals. Examples of crystals are presented in which the beam intensity can be increased by a factor of 5–10 at sufficiently high frequencies, with beam divergence remaining acceptable.     

Lattice Parameter Local Determination for Trigonal,Hexagonal, and Tetragonal Crystal Systems Using Several Coplanar X-Ray Reflections

The method for determining the local lattice parameters using quasi-multiple X-ray diffraction (which was proposed and used only for crystals of the cubic system) has been expanded to measure the local crystal lattice parameters for the trigonal, hexagonal, and tetragonal systems. Local variations in the lattice parameters in the tetragonal paratellurite (TeO₂) and trigonal lanthanum-gallium tantalate (La₃Ga_5.5Ta_0.5O₁₄) crystals have been investigated. Reflections necessary for implementing the quasi-multiple X-ray diffraction scheme are found for these crystals. The pairs of reflections that were found were used to complete quasi-multiple X-ray diffraction schemes on a laboratory X-ray source and determine the variation in the lattice parameter a along the surface of these crystals. The relative measurement error was 4 x 10^-6 at a spatial resolution of 140 μm. The accuracy of the method and the parameters determining this characteristic were analyzed based on the results. The locality of the method and the limits of the spatial resolution of an X-ray diffraction measurement of lattice parameters are estimated.     

Crystal growth and optical properties of LuYAG:Ce single crystal

Crystals of Ce³⁺-doped (Lu_xY_1?x)₃Al₅O₁₂ (LuYAG) have been grown and studied by X-ray powder diffraction, emission spectroscopy, excitation spectroscopy and X-ray excited fluorescence spectroscopy. The X-ray powder diffraction pattern revealed that the as-grown LuYAG:Ce crystal possessed the garnet structure. Compared with Ce³⁺-doped Y₃Al₅O₁₂ (YAG), the absorption bands associated with the 4f–5d transition shifted to shorter wavelengths, the emission band that originated from a transition from the lowest 5d level to the ²F ground state of the Ce³⁺ ions shifted to the blue, which was probably due to a larger Stokes shift of the emission, and the reduction of relative intensity of antisite defect emission in the X-ray excited fluorescence spectra revealed that introducing Lu ions into YAG could reduce the antisite defect.     

Bilayered Super-Structures of Antiferroelectric Mesogens

Abstract

Crystal structures of two antiferroelectric mesogens, TFMHPBC and MHPBC-10, were analysed by an X-ray diffraction method. In both crystals, mesogen molecules formed a herringbone structure which was essentially the same as that proposed for the antiferroelectric liquid crystal phase. Because of the crystallographic 2₁-symmetry along the b-axis, only the b-axis component of the dipole moment remains in a smectic layer. Since the dipole moment in the next layer has the same magnitude but the opposite direction, both crystals show no dipole moment as a whole. These structural features observed in their crystal states seem to be conserved in their antiferroelectric liquid crystal phases which are just above their crystal phases.     

Growth and scintillation properties of the Na2W2O7 crystal

The growth and scintillation properties of the Na₂W₂O₇ crystal are reported. The solid reaction between Na₂CO₃ and WO₃ is used to synthesise the Na₂W₂O₇ material. The Na₂W₂O₇ single crystal has been grown by the Bridgman method. And the Na₂W₂O₇ single crystal with sizes 14×7×6 mm³ has been achieved. The transmission spectra, the Ultraviolet fluorescence spectra and the X-ray excited luminescence spectra of the Na₂W₂O₇ crystal are measured. The measurement results show that the Na₂W₂O₇ crystal is a promising intrinsic scintillator.     

Elastic constant measurements of super ionic LiKSO4:Na single crystals

Elastic properties of sodium doped Lithium potassium sulphate, Li K_0.9 Na _0.1 SO_4, crystal has been studied by ultrasonic Pulse Echo Overlap [PEO] technique and are reported for the first time. The controversy regarding the type of crystal found while growth is performed at 35 °C with equimolar fraction of Li₂SO₄H₂O, K₂SO₄ and Na₂SO₄ has been resolved by studying the elastic properties. The importance of this crystal is that it exhibits pyroelectric, ferroelectric and electro optic properties. It is simultaneously ferroelastic and superionic. The elastic properties of LiK_0.9Na_0.1SO₄ crystal are well studied by measuring ultrasonic velocity in the crystal in certain specified crystallographic directions and evaluating the elastic stiffness constants, compliance constants and Poisson's ratios. The anisotropy in the elastic properties of the crystal are well explained by the pictorial representation of the surface plots of phase velocity, slowness and linear compressibility in a‐b and a‐c planes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The hydrogen bonding in 1-ethynyl-2-(2′-carbethoxy-1′-vinyl)-2,3-dimethyl-6-isopropyl-cyclohexan-1-ol

The X-ray crystal structure of the title compound, C₁₈H₂₈O₃, is determined. The hydrogen bond scheme does not follow considerations based on hierarchies of donor and acceptor strengths. The hydroxyl group of the molecule accepts only very weak C–H···O interactions.     

Luminescence of GeO2 glass, rutile-like and α-quartz-like crystals

The luminescence of GeO₂ rutile-like crystals was studied. Crystals were grown from a melt of germanium dioxide and sodium bicarbonate mixture. Luminescence of the crystal was compared with that of sodium germanate glasses produced in reduced and oxidized conditions. A luminescence band at 2.3 eV was observed under N₂ laser (337 nm). At higher excitation photon energies and X-ray excitation an additional band at 3 eV appears in luminescence. The band at 2.3 eV possesses intra-center decay time constant about 100 μs at 290 K and about 200 μs at low temperature. Analogous luminescence was obtained in reduced sodium germanate glasses. No luminescence was observed in oxidized glasses under nitrogen laser, therefore the luminescence of rutile-like crystal and reduced sodium germanate glass was ascribed to oxygen-deficient luminescence center modified by sodium. The band at 2.3 eV could be ascribed to triplet-singlet transition of this center, whereas the band at 3 eV, possessing decay about 0.2 μs, could be ascribed to singlet-singlet transitions. Both bands could be excited in recombination process with decay kinetics determined by traps, when excitation realized by ArF laser or ionizing irradiation with X-ray or electron beam. Another luminescence band at 3.9 eV in GeO₂ rutile-like crystal was obtained under ArF laser in the range 100-15 K. Damaging e-beam irradiation of GeO₂ crystal with α-quartz structure induces similar luminescence band.     

Thermally Stimulated Luminescence of Montmorillonite Clay

X-ray excited luminescence (XL) spectra of montmorillonite clay at RT showed a broad emission band around 380 nm with two shoulders at 340, 450 nm eitherside two sharp peaks and two shoulders are seen at 465, 487, and 548, 576 nm, respectively. The 548 and 576 nm peaks enhanced their intensity at LNT. Whereas thermally stimulated luminescence (TSL) revealed an intense glow peak at 355 K and a weak shoulder around 400 K. Room temperature annealing studies indicated that the 355 K glow peak is not as stable as 400 K shoulder which turns out to be a peak on RT annealing. The X-ray excited luminescence has been attributed to radiative recombination of electrons with holes which are associated with SiO^3-₄, AlO^4-₄ radicals and divalent impurities available in the naturally available clay. TSL is also understood on similar lines. Glow peak reactions are proposed tentatively and their trap parameters have been calculated.     

Growth of large-sized Ce:Y3Al5O12 (Ce:YAG) scintillation crystal by the temperature gradient technique (TGT)

In this work, Ce:YAG crystal with the size of ?4 in was successfully grown by the TGT method. The optical and scintillation properties of as-grown Ce:YAG crystals were investigated. Three obvious absorption bands at 223, 340 and 460 nm and two weak color-center absorption bands at 296 and 370 nm are observed in as-grown Ce:YAG crystal. Fluorescence with an emission peak at 398 nm is observed due to the color centers, and absorption bands of the color centers can be eliminated by annealing in O₂ or H₂ atmosphere at 1673 K for 24 h. Yellow-green fluorescence centered at 530 nm is found when the crystal was excited at 460 nm and the 530 nm excitation spectrum shows two peaks at 340 and 460 nm. X-ray fluorescence spectrum of as-grown crystal shows three emission peaks at 300, 360 and 530 nm. An average light output of 1360 phe/MeV and a single exponential decay with the decay time constant of 62.97 ns are found in as-grown Ce:YAG crystal.     

Variation of fluorescence intensities and lifetime of Sm3+ and Tb3+ with As2O3 content in arsenic borax glasses

Fluorescence spectra and lifetimes of Sm³⁺ and Tb³⁺ were measured in borax, As₂O₃ and borax containing 20, 50 and 80 wt% of As₂O₃. For all compositions, with the exception of pure As₂O₃, glasses were formed. In the latter case, a crystal of TbAsO₄ was obtained as detected by X-ray diffraction. A gradual increase, up to a factor of three, of fluorescence was observed on addition of As₂O₃ to borax glass. In addition to optical excitations, glasses of various compositions containing Tb³⁺ were excited by an electron beam source.     

X-ray focusing by bent crystals in Bragg backscattering

Focusing of a spherical X-ray wave in Bragg backscattering from weakly and strongly bent crystals is considered theoretically. The analytical formula describing the dimensions of the diffraction backscattering region is obtained. It is shown that, along with the well-known Johann scheme, the use of the backscattering scheme allows one to increase the aperture ratio of the crystal optics by two to three orders of magnitude. The spectral characteristics of bent crystals providing diffraction backscattering (θ = π/2) are discussed. It is shown that the spectral resolution can attain a value of the order of 10^?11.