Christian Jooss

High-quality HTS tiles designed for the application in magnetic bearings of cryotanks and flywheels

High quality bulk YBaCuO superconductors with maximum trapped fields up to 1.3 T and transport critical current densities up to 1.3 A/cm/sup 2/ in self field at 77 K are prepared by the Top Seeded Melt Growth. On the basis of this process two methods for the processing of large tiles and tiles in complex shapes are presented. Superconducting rings with a radial orientation of the crystallographic c-axis are processed by a multi-seeding method. These rings are used in the magnetic bearing of a cryotank designed for the storage of liquid hydrogen. The joining of single domains with an ErBaCuO compound leads to the formation of a superconducting joint between single domains. Large tiles prepared by this process are to be used in the circumferential magnetic bearing of a flywheel.

Oxygen Evolution at Manganite Perovskite Ruddlesden-Popper Type Particles: Trends of Activity on Structure, Valence and Covalence

An improved understanding of the correlation between the electronic properties of Mn-O bonds, activity and stability of electro-catalysts for the oxygen evolution reaction (OER) is of great importance for an improved catalyst design. Here, an in-depth study of the relation between lattice structure, electronic properties and catalyst performance of the perovskite Ca1−xPrxMnO3 and the first-order RP-system Ca2−xPrxMnO4 at doping levels of x = 0, 0.25 and 0.5 is presented. Lattice structure is determined by X-ray powder diffraction and Rietveld refinement. X-ray absorption spectroscopy of Mn-L and O-K edges gives access to Mn valence and covalency of the Mn-O bond. Oxygen evolution activity and stability is measured by rotating ring disc electrode studies. We demonstrate that the highest activity and stability coincidences for systems with a Mn-valence state of +3.7, though also requiring that the covalency of the Mn-O bond has a relative minimum. This observation points to an oxygen evolution mechanism with high redox activity of Mn. Covalency should be large enough for facile electron transfer from adsorbed oxygen species to the MnO6 network; however, it should not be hampered by oxidation of the lattice oxygen, which might cause a crossover to material degradation. Since valence and covalency changes are not entirely independent, the introduction of the energy position of the eg↑ pre-edge peak in the O-K spectra as a new descriptor for oxygen evolution is suggested, leading to a volcano-like representation of the OER activity.

Room-temperature preparation of biaxially textured indium tin oxide thin films with ion-beam-assisted deposition

Biaxially aligned indium tin oxide (ITO) thin films were prepared by an ion-beam-assisted deposition (IBAD) process at room temperature. Films with a transmittance at 550 nm of 90% and an electrical resistivity of 1.1 x 10 - 3 Ωcm for 300 and 250 nm thickness were obtained. Investigations of the texture evolution during IBAD film growth were carried out and compared to the well-established texture development in yttria-stabilized zirconia. An in-plane texture of 12.6° full width at half-maximum (FWHM) for a 1-μm-thick IBAD-ITO film was achieved. The quality of these films as electrically conductive buffer layers for YBa 2 Cu 3 O 7 - Φ (YBCO) high-temperature superconductors was demonstrated by the subsequent deposition of high-current carrying YBCO films by thermal co-evaporation using a 3-5-nm-thick Y 2 O 3 interlayer. A J C of 0.76 MA/cm 2 (77K, 0 T) was obtained for a I x 1 cm sample with ITO of 20° FWHM.

Current-voltage characteristics of manganite-titanite perovskite junctions

Summary After a general introduction into the Shockley theory of current voltage (J–V) characteristics of inorganic and organic semiconductor junctions of different bandwidth, we apply the Shockley theory-based, one diode model to a new type of perovskite junctions with polaronic charge carriers. In particular, we studied manganite–titanate p–n heterojunctions made of n-doped SrTi1− yNbyO3, y = 0.002 and p-doped Pr1− xCaxMnO3, x = 0.34 having a strongly correlated electron system. The diffusion length of the polaron carriers was analyzed by electron beam-induced current (EBIC) in a thin cross plane lamella of the junction. In the J–V characteristics, the polaronic nature of the charge carriers is exhibited mainly by the temperature dependence of the microscopic parameters, such as the hopping mobility of the series resistance and a colossal electro-resistance (CER) effect in the parallel resistance. We conclude that a modification of the Shockley equation incorporating voltage-dependent microscopic polaron parameters is required. Specifically, the voltage dependence of the reverse saturation current density is analyzed and interpreted as a voltage-dependent electron–polaron hole–polaron pair generation and separation at the interface.

Electronic structure of Pr1−xCaxMnO3

The electronic structure of

An endstation for resonant inelastic X-ray scattering studies of solid and liquid samples.

{\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}

Natural and artificial low angle grain boundaries with high current-carrying capabilities

has been investigated using a combination of first-principles calculations, x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS), electron-energy loss spectroscopy (EELS), and optical absorption. The full range of compositions,

ETEM Studies of Electrodes and Electro-catalysts

x=0,1/2,1

Strain driven phase decomposition in ion-beam sputtered Pr 1− x Ca x MnO 3 films

, and a variety of magnetic orders have been covered. Jahn-Teller as well as Zener polaron orders are considered. The free parameters of the local hybrid density functionals used in this study have been determined by comparison with measured XPS spectra. A model Hamiltonian, valid for the entire doping range, has been extracted. A simple local-orbital picture of the electronic structure for the interpretation of experimental spectra is provided. The comparison of theoretical calculations and different experimental spectra provide a detailed and consistent picture of the electronic structure. The large variations of measured optical absorption spectra are traced back to the co-existence of magnetic orders (respectively, to the occupation of local orbitals). A consistent treatment of the Coulomb interaction indicates a partial cancellation of Coulomb parameters and supports the dominance of the electron-phonon coupling.

Magnetostatic interaction mechanisms in a two-dimensional composite magnet

A novel experimental setup is presented for resonant inelastic X-ray scattering investigations of solid and liquid samples in the soft X-ray region for studying the complex electronic configuration of (bio)chemical systems. The uniqueness of the apparatus is its high flexibility combined with optimal energy resolution and energy range ratio. The apparatus enables investigation of chemical analyses, which reflects the chemical imprints. The endstation is composed of a main sample chamber, a sample holder for either solid or liquid jet delivery system, and a soft X-ray grating spectrometer for 210-1250 eV with a resolving power of ∼1000. It combines for the first time liquid jet technology with a soft X-ray spectrometer based on the variable line spacing principle. This setup was commissioned at the soft X-ray beamline P04 at PETRA III of the Deutsches Elektronen-Synchrotron in Hamburg which is currently the most brilliant storage-ring-based X-ray radiation source in the world. The first results of liquid and solid samples show that this setup allows the detection of photons across an energy range of ∼300 eV. This covers simultaneously the emission lines of life-important elements like carbon, nitrogen and oxygen in a shot-based procedure.