A high-pressure Raman and X-ray diffraction study of the perovskite SrCeO3

A high-pressure structural study of SrCeO₃ has been performed at room temperature by Raman spectroscopy and X-ray diffraction up to 32 and 45 GPa, respectively. A first-order reversible phase transition is observed at about 12 GPa in both techniques. A second weak structural change, taking place between 18 and 25 GPa, can be suspected from Raman data. The increase in the number of Raman bands and diffraction lines is an indication that the symmetry is lowered and the compound does not evolve towards the ideal cubic perovskite structure. A Rietveld analysis of X-ray data was performed for the low-pressure phase and the atomic positions and the cell lattice parameters variations are reported in this paper. The volume compressibility derived from Raman modes (5.6×10⁻¹² Pa⁻¹), involving mainly bond-stretching for each type of polyhedron, is found to be close to the one obtained from volume cell variations measured by X-ray diffraction (7.9×10⁻¹² Pa⁻¹).     

类锂离子与软X射线激光研究有关的跃迁波长和振子强度

本文用多组态HXR自洽场方法和优化以Slater径向积分法相结计算了类锂离子(Z=13～17,19)1s~2nl~2LJ(2≤n≤5,0≤l≤4)能级之间的跃迁波长和振子强度,并和实验进行了比较。就软X射线激光跃迁4f—3d而言,本文计算的波长值比其它文献的计算值更接近于观测值。     

Effects of UV photon irradiation on SiOx (0 < x < 2) structural properties

Thin films of a-SiO_x (0 < x < 2) were prepared by reactive r.f. magnetron sputtering from a polycrystalline-silicon target in an Ar/O₂ gas mixture. The oxygen partial pressure in the deposition chamber was varied so as to obtain films with different values of x. The plasma was monitored, during depositions, by optical emission spectroscopy (OES) system. Energy dispersive X-ray (EDX) measurements and infra-red (IR) spectroscopy were used to study the compositional and structural properties of the deposited layers.Structural modifications of SiO_x thin films have been induced by UV photons’ bombardment (wavelength of 248 nm) using a pulsed laser. IR spectroscopy and X-ray photoemission spectroscopy (XPS) were used to investigate the structural changes as a function of x value and incident energy. SiO_x phase separation by spinodal decomposition was revealed. The IR peak position shifted towards high wavenumber values when the laser energy is increased. Values corresponding to the SiO₂ material (only Si⁴⁺) have been found for laser irradiated samples, independently on the original x value. The phase separation process has a threshold energy that is in agreement with theoretical values calculated for the dissociation energy of the investigated material.For high values of the laser energy, crystalline silicon embedded in oxygen-rich silicon oxide was revealed by Raman spectroscopy.     

Amorphous Fe–Mg alloy thin films: magnetic properties and atomic vibrational dynamics

Amorphous (a-) Fe _x Mg_1?x alloys are interesting materials for the investigation of non-Debye-like low-energy vibrational excitations. We have prepared a-Fe _x Mg_1?x alloy thin films (0.3 ≤ × ≤0.7) by vapour quenching. The amorphous state was confirmed by conversion electron Mössbauer spectroscopy between 4.2–300 K, and the x- and temperature-dependence of the isomer shift and hyperfine magnetic field was measured. For x= 0.6 and 0.7, magnetic ordering occurs below ~150 K. The atomic vibrational density of states, g(E), was determined by nuclear resonant inelastic scattering, providing clear evidence for the non-Debye-like low-energy vibrational excitations.     

Study of photon-induced L3 vacancy alignment for elements La to U

Alignment of photon-induced L₃ vacancies is studied in rare earth and highZ elements at energies of experimental interest, near thresholds to 60 keV, under nonrelativistic dipole approximation. Numerical calculations of the matrix element are undertaken to produce theoretical data for comparison with the experimental findings. The A₂ values being s>0.1 at photoelectron energies <20 keV are certainly higher than 5–8% uncertainties quoted in experimental results. Present findings are from a very basic model, hydrogen-like and can further be treated as reference to observe the impact of screening, relativistic, multipole and retardation corrections to the model     

Study on Phase-Formation Mechanism and Intergrowth for Bi(Pb)-Sr-Ca-Cu-O System

In this paper, the phase-formation mechanism of Bi-based superconductors was systematically investigated by using high-temperature X-ray diffraction, differential thermal analysis (DTA) and crystallization of amorphous state. The transformations among Bi-based 2201, 2212 and 2223 phases were observed, and the intergrown phenomenon of the 2201, 2212 and 2223 phases was explained. It was proposed that there exist a composition equilibrium between 2212 phase and Ca2CuO3 and a competition of thermody-namic stability among Ca2CuO3, 2212 and 2223 phases. This is why it is difficult to prepare the 2223 phase. After Pb was doped in Bi-Sr-Ca-Cu-O system, Ca2CuO3 phase in the Bi-Sr-Ca-Cu-O system was replaced by Ca2PbO4, so that the composition equilibrium and competition of thermodynamic stability mentioned above were avoided.     

Cubane derivatives 1. Synthesis and molecular structures of the esters of 1,4-cubanedicarboxylic acid

An effective method of esterification of 1,4-cubanedicarboxylic acid with alkylsulfuric acids is proposed. The derivatives of alkanols with substantially different pK_a Valus are obtained in high yields. Molecular structures of the esters obtained are confirmed by various methods. The X-ray study showed a remarkable effect of the nature of an alkyl radical on the geometry of the cubane core.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.668–672, April, 1994.The authors thank Dr. G. V. Lagodzinskaya for analyzing the NMR spectra and for useful discussions.     

DTA and X-ray diffraction investigations of laser-irradiated CeO2 powders

The TG and DTA curves and diffractograms of powdered CeO₂ samples irradiated with a CO₂ laser beam with powers of 0.41–1.39 kW/cm² are presented. The laser treatment induced structural changes and probably generation of a metastable phase. X-ray diffraction coupled with thermal analysis was used to establish the structural modifications in the irradiated samples after heating.     

Azine bridged silver coordination polymers: Powder X-ray diffraction route to crystal structure determination of silver benzotriazole

In continuation of our interest in solid-state structures of silver complexes of photographic importance, the structure for silver benzotriazole (AgBZT), has now been obtained. The preferred method for solving crystal structures is via single-crystal X-ray diffraction (XRD). However, for some materials, growing single crystals of appropriate size and quality is often difficult or even impossible. AgBZT is an example of such a silver complex with poor solubility. The usual routes to preparing single crystals using recrystallization from a cooperating solvent resulted in polycrystalline powder samples. We propose a crystal structure for AgBZT, solved from synchrotron X-ray powder diffraction data, using a direct-space Monte Carlo simulated annealing approach. AgBZT crystals are monoclinic, (P2₁/c), with unit cell dimensions, a=14.8052(3) Å, b=3.7498(4) Å, c=12.3495(12) Å, and β=114.200(6)°. The AgBZT complex is constructed from all three of the Benzotriazole (BZT) nitrogens bonding to a separate silver atom. As a consequence of this bonding mode, the structure is a highly cross-linked, coordination polymer.     

Synthesis of ZnAl2O4/α-Al2O3 complex substrates and growth of GaN films

With the solid phase reaction between pulsed-laser-deposited (PLD) ZnOfilm and α-Al2O3 substrate, ZnAl2O4/α-Al2O3 complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl2O4 changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding scanning electron microscope (SEM)images indicate that the surface morphology of ZnAl2O4 transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRDspectra present that ZnAl2O4 prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl2O4/α-Al2O3 substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD). XRD spectra indicate that GaN film on this kind of complex substrate changes from c-axis single crystal to poly-crystal as ZnAl2O4 layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results indicate that islands on thin ZnAl2O4 layer can promote nucleation at initial stage of GaN growth, which leadsto the (0001)-oriented GaN film.