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[en] Ab initio theories of electric transport in solid systems with reduced dimensions, i.e., systems that at best are characterized by two-dimensional translational invariance, are reviewed in terms of a fully relativistic description of the Kubo-Greenwood equation. As the use of this equation requires concepts such as collinearity and non-collinearity in order to properly define resistivities or resistances corresponding to particular magnetic configurations, respective consequences of the (local) density functional theory are recalled in quite a detailed manner. Furthermore, since theoretical descriptions of solid systems with reduced dimensions require quantum mechanical methods different from bulk systems (three-dimensional periodicity), the so-called Screened Korringa-Kohn-Rostoker (SKKR-) method for layered systems is introduced together with a matching coherent potential approximation (inhomogeneous CPA). The applications shown are mainly meant to illustrate various aspects of electric transport in solid systems with reduced dimensions and comprise not only current-in-plane (CIP) experiments, but also current perpendicular to the planes of atoms geometries, consequences of tunneling, and finite nanostructures at or on metallic substrates. In order to give a more complete view of available ab initio methods also a non-relativistic approach based on the Tight Binding Linear Combination of muffin tin orbitals (TB-LMTO-) method and the so-called Kubo-Landauer equation in terms of transmission and reflection matrices is presented. A compilation of references with respect to ab-initio type approaches not explicitly discussed in here finally concludes the discussion of electric properties in solid systems with reduced dimensions
[en] Iron(III) complexes of the Schiff base 4-N-(4'-antipyrylmethylidene)aminoantipyrine (AA) with counter ions, such as, perchlorate, nitrate, thiocyanate, chloride and bromide have been prepared and characterized by elemental analyses, electrical conductance in non-aqueous solvents, IR and electronic spectra, magnetic susceptibility measurements as well as by thermogravimetric analysis. The complexes have the general formulae [Fe(AA)2(ClO4)](ClO4)2, [Fe(AA)2X2]X (X=NO3- or Br-) and [Fe(AA)X3] (X=SCN- or Cl-). In complexes, AA acts as a neutral bidentate ligand, coordinating through one of the carbonyl oxygens and azomethine nitrogen in perchlorate, nitrate and bromide complexes while the coordination of AA occurs in a neutral tridentate fashion through both carbonyl oxygens and azomethine nitrogen in thiocyanate and chloride complexes. In the perchlorate complex, one of the perchlorate ions is coordinated bidentately while in the nitrate complex two of the nitrate ions are coordinated monodentately to the metal ion. In the thiocyanate and chloride complexes all the anions are coordinated while in the bromide complex two of the bromide ions are coordinated. A high spin octahedral geometry is assigned to the iron(III) ion in all these complexes. The phenomenological, kinetic and mechanistic aspects of the nitrate, thiocyanate, chloride and bromide complexes were studied by TG and DTG techniques. The kinetic parameters like activation energy, pre-exponential factor and entropy of activation were also computed. The rate controlling process in all stages of decomposition is random nucleation with one on each particle (Mampel model) [Thermochim. Acta 2 (1971) 423]
[en] Starting from an algebraic description of collinearity within density functional theory the concept of magnetic configurations is introduced, which in turn is of crucial importance to define the interlayer exchange energy (IEC) and the (giant) magnetoresistance (GMR). The applications shown are meant to clarify not only the conceptual basis of IEC and GMR, but also the difficulties that can arise in actual calculations
[en] Two novel nitrogen-rich lanthanide compounds of 5,5'-(azobis)tetrazolide (ZT) were synthesized and structurally characterized. The dinuclear, isostructural compounds [Ce(ZT)CO(HO)]·4HO (1) and [Pr(ZT)CO(HO)]·4HO (2) were synthesized via two independent routes. Compound 1 was obtained after partial Lewis acidic decomposition of ZT by Ce in aqueous solution of (NH)Ce(NO) and NaZT. Compound 2 was obtained by crystallization from aqueous solutions of Pr(NO), NaZT, and NaCO. By X-ray diffraction analysis at 200 K, it was found that the trivalent lanthanide cations are bridged by a bidentate carbonato ligand and each cation is further coordinated by six HO ligands and one ZT ligand thus being ninefold coordinated. (© 2020 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley‐VCH GmbH)
[en] There are many examples in theoretical physics where a fundamental quantity can be considered a quadratic form ρ=Σiρi=vertical bar Ψ vertical bar2 and the corresponding linear form Ψ=Σiψi is highly relevant for the physical problem under study. This, in particular, is the case of the density and the wave function in quantum mechanics. In the study of N-identical-fermion systems we have the additional feature that Ψ is a function of the 3N configuration space coordinates and ρ is defined in three-dimensional real space. For many-electron systems in the ground state the wave function and the Hamiltonian are to be expressed in terms of the configuration space (CS), a replica of real space for each electron. Here we present a geometric formulation of the CS, of the wave function, of the density, and of the Hamiltonian to compute the electronic structure of the system. Then, using the new geometric notation and the indistinguishability and equivalence of the electrons, we obtain an alternative computational method for the ground state of the system. We present the method and discuss its usefulness and relation to other approaches
[en] Thermochemical energy storage uses reversible thermochemical reactions to store and release heat, representing a promising technology for energy conservation and utilizing fluctuating renewable energy sources and waste heat. Many recent studies have focused on determination of the enthalpy of reaction of possible thermochemical materials (TCM) based on thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). So far, comparatively few attempts have been made to characterize the apparent specific heat capacity at constant pressure of the investigated TCM. The purpose of this study is to outline a measurement and analysis procedure to evaluate of powdery TCM. The procedure is presented focusing on two metal hydroxides Ca(OH)2 and Mg(OH)2. Preliminary TGA experiments were conducted to identify reaction-free temperature intervals and mass change. Starting from the metal hydroxide, subsequent DSC experiments with two consecutive heating and cooling cycles were carried out to determine of the initial hydroxide and the oxide product. Three separate DSC runs for each candidate enable an evaluation of measurement uncertainty, and results were compared to available literature data. Preliminary TGA experiments have shown that the applied heating rate β has a strong effect on the measured dehydration reaction. This result influences the consecutive interpretation of the metal hydroxides. Analysis of the measured data compared to literature show good agreement for both metal hydroxides and oxides. Overlapping endotherm effects, which are not part of , have to be considered for further thermal conductivity calculations.
[en] The crystallization of terbium 5,5"'-azobis[1H-tetrazol-1-ide] (ZT) in the presence of trace amounts (ca. 50 Bq, ca. 1.6 pmol) of americium results in 1) the accumulation of the americium tracer in the crystalline solid and 2) a material that adopts a different crystal structure to that formed in the absence of americium. Americium-doped [Tb(Am)(H_2O)_7ZT]_2 ZT.10 H_2O is isostructural to light lanthanide (Ce-Gd) 5,5"'-azobis[1H-tetrazol-1-ide] compounds, rather than to the heavy lanthanide (Tb-Lu) 5,5"'-azobis[1H-tetrazol-1-ide] (e.g., [Tb(H_2O)_8]_2ZT_3.6 H_2O) derivatives. Traces of Am seem to force the Tb compound into a structure normally preferred by the lighter lanthanides, despite a 10"8-fold Tb excess. The americium-doped material was studied by single-crystal X-ray diffraction, vibrational spectroscopy, radiochemical neutron activation analysis, and scanning electron microscopy. In addition, the inclusion properties of terbium 5,5"'-azobis[1H-tetrazol-1-ide] towards americium were quantified, and a model for the crystallization process is proposed. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] Bulk measurements of magnetic susceptibility χ and 57Fe-Moessbauer spectroscopy were used to investigate the low spin (LS) to high spin (HS) transition caused by temperature changes for different mono- and polynuclear Fe(II) complexes based on the extremely versatile class of 1-substituted tetrazoles. The influence of length and rigidity of different terminating and bridging ligands is shown.
[en] A series of rare earth element (REE) mixed-anion 5,5'-azobis(1H-tetrazol-1-ide)-carbonate ([REE2(ZT)2CO3(H2O)10].2H2O; REE = lanthanides plus yttrium) coordination compounds were synthesized, characterized, and analyzed. Syntheses by simple metathesis reactions under a CO2 atmosphere were carried out at ambient (La-Gd and Ho) and elevated pressures (55 bar; Tb, Dy, Er, Tm, Yb, and Y). The resulting crystalline materials were characterized principally by single-crystal X-ray diffraction and vibrational spectroscopy (infrared and Raman). All materials are structurally isotypic, crystallizing in the space group C2/c and show nearly identical spectroscopic properties for all the elements investigated. Cell parameters, bond lengths, and bond angles differ marginally, revealing only a slight variation coinciding with the lanthanide (Ln) contraction, that is, the change in the ionic radii of the trivalent rare earth elements. The herein reported series of rare earth element azobis[tetrazolide]-carbonates represents a remarkable exception as they are a series of isotypic REE coordination compounds with tetrazolide-derived ligands unaffected by the ''gadolinium break''. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)