Volume 50, Issue 6

Complete ionic conductivity spectra as well as quasielastic and inelastic neutron scattering spectra have been taken of solid silver bromide at various temperatures. High-amplitude vibrational move­ments, essentially of the silver ions, contribute to both kinds of spectra. In particular, a conductivity maximum, located at about 500 GHz, reflects oscillations of individual silver ions along directions. -The microwave and millimetre-wave conductivities are dominated by a thermally activated Debye-type relaxation process. The effect is consistently explained by the frequent hopping of silver ions from regular octahedral lattice sites into tetrahedral interstitial sites and back again, i.e., by the frequent creation and recombination of Frenkel pairs. -The effect is also responsible for the existence of thermally activated quasielastic components in the neutron scattering spectra. The width of the coherent quasielastic scattering shows that the forward-backward hopping of a silver ion is accompanied by fast correlated movements of ions in its immediate neighbourhood.

A variation of the commonly used polynomial interpolation formulae for the excess functions of binary mixtures is proposed, in which the cross-calculation of the coefficients of partial and integral molar functions is greatly facilitated.

Decomposition morphologies of supersaturated spinel solid solutions in the quasi-binary system Co 2 TiO 4 -CoAl 2 O 4 at 973 K show all pertinent features of spinodal decomposition. Since the decomposition morphology may not be considered as sufficient evidence for a spinodal process, the thermodynamics of the spinel solid solutions and the linear transport theory of spinodal decomposition were combined to corroborate the experimental results of the early decomposition reaction. Simultaneous ordering, a common property of ternary and higher nonequilibrium solid solutions, was also observed. These ordering processes occur locally in distinct regions of the spinel crystal. Moreover, the spinodal wavelength λ increases in time according to λ ∞ t, which is unusual and will be discussed in the light of cation diffusion in semiconducting oxides with two cation sublattices.

Characteristic secondary ion emission patterns of several metal-hydrogen systems have been measured by SIMS to get information about the metal-hydrogen bonding and the structure of these systems. Results on SmCo 5 D n and LaNi 5 H n , and on H-D-loaded samples of the pure components are presented. The emission patterns of the secondary ions show a stronger bonding of hydrogen to Co and Ni than to Sm and La, although these transition metals, contrary to Sm or La, do not form stable hydrides under normal conditions. In these AB 5 -compounds the transition metal seems to be transformed to a "hydride forming material" due to the presence of the rare earth element. The secondary ion emission patterns of the hydrogen loaded intermetallics are explained and compared to those of the hydrogen loaded pure components. The similarity in the secondary ion emission patterns of the SmCo 5 D n and LaNi 5 H n systems points to a general characteristic of AB 5 H n materials.

Perovskite structured strontium cerate doped with ytterbium and water, e.g. SrCe 0.95 Yb 0.05 H 0.02 O 2.985 , is a well known proton conductor at elevated temperatures. We have studied its proton conductivity or diffusivity, respectively, by impedance spectroscopy, IS, and by quasielastic neutron scattering, QENS. While the former method yields a macroscopic proton diffusion coefficient, the latter method allows to elucidate the microscopic proton diffusion mechanism. It consists of a sequence of free diffusion and trapping/escape events with the Yb 3+ ions acting as trapping centers. The self-diffusion coefficient obtained with QENS agrees with the conductivity diffusion coefficient obtained with IS.

A new evaluation method is presented to analyse the temperature dependance of reactions with rates that can be separated into a temperature dependent and a concentration dependent part. The proposed method allows to evaluate isothermal, adiabatic, isoperibolic and temperature programmed measurements in an unified manner. To determine the activation energy an Arrhenius law but no explicite kinetic model has to be assumed. The application of the method is demonstrated using experimental data of different reactions from former investigations.

The Born-Haber Cycle (BHC) is critically reviewed, the origin of severe limitations in its appli­ cation is shown. Partly this is based on the construction of the third step, partly it is connected with the fact that most of the "classical" anions of inorganic chemistry are instable, "unobservable" gaseous entities. The Madelung Part of Lattice Energy, MAPLE*, is extentionally analyzed (e.g. TiO 2 ) to demonstrate that the similarity of thermodynamical properties like ΔH° 298 of all modifica­ tions, reflected in MAPLE, is non-trivial. The analogous analysis with e.g. BaTiO 3 proves that neither the classical "central ion" (here Ti 4+ ) nor the "completing" cation (here Ba 2+ ) but the "anions" coordinating the last mentioned cation BaO gain energy and, in this sense, "stabilize" the complex. Even simple compounds (e.g. A-La 2 O 3 ) show surprising geometrical arrangements, in striking contrast to often used but simple minded concepts like "Bond Length/Bond Strength" and its derivatives like CHARDI, whereas such "oddities" are explained by MAPLE. The application of the theorem of additivity of MAPLE (MAPLE polynary = Σ MAPLE binary ), that passes even in the case of hydrates, and its limitations are discussed. Guided by MAPLE, surprisingly complicated structures (e.g. Cs 2 Li 3 I 5 ) of polynary derivatives of structurally exceedingly simple binary com­ pounds become "understandable". If "molecular" entities like SO 3 are involved, limitations can be excluded using "increments". Last not least, MAPLE is the first known guide to a multi-dimen-sional but strict scheme of characterisation of Solid State Structures in the sense of Linne's ideas, based on geometrical facts only.

Experimentally determined temperature and concentration profiles in a wall-cooled fixed-bed catalytic reactor are modelled equally well by the quasihomogeneous and heterogeneous model at a Reynolds number of Rep = 32. In both cases the good agreement between measured and calculated data is only achieved if the equations are solved for a radially uneven flow distribution and for a boundary condition at the reactor wall ensuring the same temperature of catalyst and wall at the contact point. The numerical solutions of the two-phase model demonstrate that the differences between solid and fluid temperature are low, even in the presence of a highly exothermic reaction like the oxidation of ethane.

Using a relation between representation theory of crystallographic space groups and a Dirichlet type of boundary problem for the Laplacian, we derive the solutions for the Dirichlet problem, as well as for a similar Neumann boundary problem, by a complete decomposition of plane waves into irreducible representations of a particular space group. This decomposition corresponds to a basis transformation in L 2 (Ω) and yields a new set of basis functions adapted to the symmetry of the lattice considered.

Proton and fluorine NMR second moments and spin-lattice relaxation times for polycrystalline tetraethyl-and tetrapropylammonium tetrafluoroborates have been measured over a wide range of temperatures. Solid-solid phase transitions were found for both compounds and confirmed by DSC. Methyl group C 3 reorientation followed by more complex cation motions was evidenced in the low temperature phases. Overall cation reorientation characterises the high temperature phases of both compounds. Isotropic anion reorientation was found in both salts in both phases.

Preparation of a cholesteric liquid crystalline phase in planar orienting liquid crystal cells exhibits discontinuous colour changes with temperature when viewed between crossed polarizers. The trans­ mission spectra of such a system can be described by a modified de Vries equation, with the birefringence dispersion included in a simplified single-band model. With a suitable choice of the cell gap as compared to the cholesteric pitch, the procedure can be used as a new method to determine the temperature dependence of the cholesteric pitch.

The time domain spectroscopy (TDS) method has been used for the measurement of the complex dielectric permittivity in the isotropic phase and for perpendicular and parallel orientations in the nematic phase of 5PCH (4-(trans-4-pentyl-cyclohexyl)-benzonitrile). The accessible frequencies range from ca 15 MHz to ca. 1.5 GHz. The obtained spectra are well consistent with the spectra measured recently in the frequency domain (T. Brückert et al., Mol. Cryst. Liq. Cryst., in press). From the relaxation times τ ‖, τ ⊥ and τ is we have calculated the activation enthalpies and the retardation factors g || and g ⊥ that allow to obtain the nematic potential q. The validity of some assump­ tions of the mean-field theories of the nematic state are discussed.

In the Planck aether hypothesis it is assumed that space is densely filled with an equal number of locally interacting positive and negative Planck masses obeying a nonrelativistic law of motion. If described by a quantum mechanical two-component nonrelativistic nonlinear operator field equation, this model has a spectrum of particles greatly resembling the particles of the standard model, with Lorentz invariance as a derived dynamical symmetry valid in the limit of energies small com­ pared to the Planck energy. Here we show that quantum mechanics itself can be derived from the Newtonian mechanics of the Planck aether as an approximate solution of the Boltzmann equation for the positive and negative Planck masses, with departures from quantum mechanics suppressed by the Planck length.