[en] Polycrystalline LiBH₄ has been studied by Raman spectroscopy in the temperature interval 295-412 K and the frequency range 2700-130 cm^-1. The Raman active modes are consistent with the presence of a (BH₄)^- ion having a distorted tetrahedral configuration. As the temperature is increased the sudden disappearance of mode splitting points to the onset of a structural phase transition that leads to a higher local symmetry of the (BH₄)^- tetrahedron. The transition occurs at ∼384 K, is of first-order and has a hysteresis of about 8 K. A strong and discontinuous broadening of bands remaining after the transition suggests the onset of large vibrational amplitudes of the (BH₄)^- tetrahedra about their trigonal axis

[en] Ba₆Mg₁₁F₃₄, a new compound of the pseudobinary BaF₂-MgF₂ system, has been synthesized by solid state techniques from stoichiometric amounts of BaF₂ and MgF₂ and its crystal structure determined by single crystal X-ray diffraction (space group P1-bar, a=7.5084(6), b=9.9192(8), c=10.0354(8) A, α=81.563(2), β=72.402(2), γ=71.198(1) deg., 3899 structure factors, 233 parameters, R(F²>2σ(F²))=0.018, wR(F² all) = 0.046). It is isotypic with the copper(II) analogue, Ba₆Cu₁₁F₃₄. The main features of the structure are a network of [MgF₆] octahedra and three different [BaF_x] polyhedra with x=12, 11+1 and 13. Ba₆Mg_11-xFe_xF₃₄ and Ba₆Mg_11-xMn_xF₃₄ solid solutions were prepared and their composition determined by single crystal structure analyses. The luminescence properties of Ba₆Mg₁₁F₃₄ doped with Eu²⁺ were studied using fluorescence spectroscopy. The observed luminescence was pale blue with a maximum at 465 nm

[en] Alkali borohydrides MBH₄ and their deuterides have been investigated by X-ray and neutron powder diffraction (M=K,Rb,Cs) and by infrared and Raman spectroscopy (M=Na,K,Rb,Cs). At room temperature the compounds crystallize with a cubic high temperature (HT) structure having Fm3-bar m symmetry in which the [BH₄]^- complexes are disordered. At low temperature (LT) the potassium compound transforms into a tetragonal low temperature structure having P4₂/n mc symmetry in which the [BH₄]^- complexes are ordered such as in the isotypic sodium congener. The B-H distances within the complex as measured on the deuteride at 1.5 K are 1.205(3) Angst. Indications for a partial ordering in the rubidium and cesium compounds exist but are not sufficient for a full structural characterization. Infrared and Raman spectra at room temperature are fully assigned for both hydrides and deuterides, including the overtones and combination bands, the Fermi resonance type interactions and the ¹⁰B to ¹¹B splitting due to the presence of natural boron in the samples

[en] Positron tomographs are often characterized by parameters like efficiency, resolution, reconstruction time, number of slices, etc. Due to differences in the method, additional information is needed when comparing conventional PET and TOFPET systems. Reconstruction gain, reduction of random coincidences, and the possibility of measuring cross slices are examined. Properties of two tomographic systems are compared and evaluated. (Author)

[en] Experiments in which the Raman linewidth was measured as a function of temperature (7-1183 K) and pressure (0-400 bar) were performed on the (111) and (100) planes of single crystals of the cubic anti-fluorite Li₂S. The temperature dependence of the lattice constant was determined by x-ray diffraction (11-295 K). From these results and published Brillouin scattering data for this host, the volume thermal expansion coefficient as a function of temperature was obtained as well as the isothermal compressibility and the isothermal Raman mode Grueneisen parameter. Using the thermodynamic approach within the quasi-harmonic approximation, we show that below 400 K the volume effects describe well the temperature dependence of the Raman linewidth whereas above this temperature there are direct anharmonic effects appearing. Above approximately 850 K new Raman lines appear that are A₁ and E polarized. (author)

[en] Trigger pulses running in phase with breathing periods are produced by means of signal differentiation in an analogue circuit. Thus equilibrium gated radionuclide lung imaging with sup(81m)Kr has been achieved, particularly suitable for ventilation studies of children which cannot cooperate in breathing manoeuvre. Regional distribution of tidal volume and asynchronism in two infants has been demonstrated. (orig.)

[en] Ksing an autofluoroscope and a dedicated data processing system time activity curves after injection of ¹³¹I-bromsulphane were generated for calculation of liver function. It was found that the method is not sufficiently reliable when using the total liver as ROI without excluding certain regions corresponding to the bile duct system. An appropriate correcting technique is to be developped before using this technique to calculate liver function. (orig.)

[en] Mixed matlokite hosts of composition BaFBr_xI_1-x(0≤x≤1) (pure and doped with Sm²⁺, Eu²⁺) were studied with x-ray crystallography, luminescence, Raman, and electron paramagnetic resonance (EPR) spectroscopy. Results are presented for BaFBr_0.5I_0.5 which demonstrate that a ferrielectric domain structure is formed due to the fact that the heavy halogen ions form separate sublattices with randomly distributed domain walls. The space group of a domain is P4 mm (No. 99). The EPR data from Eu²⁺ allowed to determine the volume fraction of domains

[en] SrMgF₄ was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF₄ was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis

[en] The structural phase transitions occurring in a series of perovskite-type complex hydrides based on the tetrahydroborate anion ${\text{BH}}_4^{-<!--\; ???\; -->}$ are investigated by means of in situ synchrotron x-ray powder diffraction, vibrational spectroscopy, thermal methods and ab initio calculations in the solid state. Structural dynamics of the $\text{B}{\text{H}}_4$ anion are followed with quasi-elastic neutron scattering. We show that unexpected temperature-induced lattice instabilities in perovskite-type ACa($\text{B}{\text{H}}_4$)₃ (A = K, Rb, Cs) have their origin in close hydridic di-hydrogen contacts. The rich lattice dynamics lead to coupling between internal B-H vibrations and phonons, resulting in distortions in the high-temperature polymorph that are identical in symmetry to well-known instabilities in oxide perovskites, generally condensing at lower temperatures. It is found that anion-substitution ${\text{BH}}_4^{-<!--\; ???\; -->}$ $\leftrightarrow <!--\; ???\; -->X^{-<!--\; ???\; -->}$ (X = Halide) can relax distortions in ACa($\text{B}{\text{H}}_4$)₃ by eliminating coulomb repulsive ${\text{H}}^{-<!--\; ???\; -->}\cdot <!--\; ???\; -->\cdot <!--\; ???\; -->\cdot <!--\; ???\; -->{\text{H}}^{-<!--\; ???\; -->}$ effects. The interesting nature of phase transition in ACa($\text{B}{\text{H}}_4$)₃ enters an unexplored field of weak interactions in ceramic-like host lattices and is the principal motivation for this study. Close di-hydrogen contacts suggest new concepts to tailor crystal symmetries in complex hydride perovskites in the future. (paper)