Johannes Birkenstock

Universität Bremen | Uni Bremen · Department of Geosciences

The development of a novel reactive spray technology based on the well-known gas phase metal oxide synthesis route provides innumerable opportunities for the production of non-oxide nanoparticles. Among these materials, metal sulfides are expected to have a high impact especially in the development of electrochemical and photochemical high surface...

Single crystals of five (Al,Ge)-mullites incorporating Pb, and four of which also incorporating foreign cations (Fe,Cr,Nd,Sm) were grown by flux techniques in a PbO-MoO3 flux. They were characterized by scanning electron microscopy, electron microprobe analyses, single-crystal X-ray diffraction. In addition, the refractive indices of mullite contai...

Na1/2Bi1/2TiO3 (NBT) with varying Bi content has gained significant interest as a potential new material for solid-oxide fuel cells and oxygen separation membranes because of its excellent oxygen-ion conductivity. In this work, the effect of varying Bi content in NBT ceramics of compositions Na1/2BixTiO2.25+1.5x, where x = 0.485–0.510, on the tempe...

The spinel LiMn2O4 (LMO) is a promising cathode material for rechargeable Li-ion batteries due to its excellent properties, including cost effectiveness, eco-friendliness, high energy density, and rate capability. The commercial application of LiMn2O4 is limited by its fast capacity fading during cycling, which lowers the electrochemical performanc...

Single crystals of ABW-type CsAlTiO4 (CAT), CsFeTiO4 (CFT), CsGaTiO4 (CGT), and ANA-type CsTi1.1Si1.9O6.5 (CST) were grown and characterized by electron microprobe analyses, single-crystal X-ray diffraction, thermal analyses, and spindle-stage optical investigations to determine the electronic polarizability of 4-coordinated Ti⁴⁺, α([4]Ti⁴⁺). The c...

A single crystal (∼ 20 µm × 20 µm × 330 µm) of mullite-2c, a natural polytype of mullite, was separated from a radially grown cluster of acicular crystals from Ettringer Bellerberg (Quarternary Eifel volcanic fields, Germany). The chemical composition determined from electron microprobe analysis (EMPA) is Na0.01Mg0.05Al8.52Fe0.293+Si3.13Ti0.02O19.5...

The controlled dissolution kinetics of iron‐doped copper oxide nanoparticles are applied in targeted nanomedicine. In their Research Article (DOI: 10.1002/anie.201912312), L. Mädler, S. J. Soenen et al. present a model‐based approach for adjusting the dissolution kinetics and intracellular release of copper that opens a therapeutic window for cance...

Die kontrollierte Auflösungskinetik Eisen‐dotierter Kupferoxid‐Nanopartikel wird in der gezielten Nanomedizin eingesetzt. In ihrem Forschungsartikel (DOI: 10.1002/ange.201912312) stellen L. Mädler, S. J. Soenen et al. einen Modell‐basierten Ansatz zur Anpassung der Auflösungskinetik und interzellulären Freigabe von Kupfer vor, der neue Krebstherapi...

The progress in nanomedicine (NM) using nanoparticles (NPs) is mainly based on drug carriers for the delivery of classical chemotherapeutics. While low NM delivery rates limit therapeutic efficacy, an entirely different approach was investigated. A homologous series of engineered CuO NPs was designed for dual purpose (carrier and drug) with a direc...

The progress in nanomedicine (NM) using nanoparticles (NPs) is mainly based on drug carriers for the delivery of classical chemotherapeutics. While low NM delivery rates limit therapeutic efficacy, an entirely different approach was investigated. A homologous series of engineered CuO NPs was designed for dual purpose (carrier and drug) with a direc...

The development and industrial application of advanced lithium-based energy storage materials are directly related to the innovative production techniques and the usage of inexpensive precursor materials. The Flame spray pyrolysis (FSP) is a promising technique that overcomes the challenges in the production processes such as scalability, process c...

Single crystals of B2O3 are needed for the precise determination of the refractive indices used to calculate the electronic polarizability α of 3-coordinated boron. The α(B) values in turn are used to predict mean refractive indices of borate minerals. Since the contribution of boron to the total polarizability of a mineral is very low, the synthet...

A crystal of BaCaBO3F was grown by the Czochralski method. It shows a phase transition at 242.7 °C upon cooling where the hexagonal high-temperature modification is transformed to a monoclinic low-temperature form (space group C2, a = 17.8779(8) Å, b = 9.0596(4) Å, c = 12.9735(5) Å, β = 118.875(13)°, V = 1840.03(22) ų, Z = 18). The monoclinic phas...

δ-Bi2O3 is one of the best oxygen ion conductors known. However, due to its limited thermal stability and complicated synthesis techniques, the applications are limited. Here, the synthesis of stable nano-sized δ-Bi2O3 using versatile and rapid flame spray pyrolysis (FSP) combined with in-situ Ti and/or Mn doping for an enhanced thermal stability i...

A mineral intermediate between sillimanite and mullite, tentatively designated as “sillimullite,” was studied by electron microprobe analyses and single-crystal X-ray diffraction methods. The chemical compositions derived from the microprobe results and the crystal-structure refinement are Al7.84Fe0.18 Ti0.03Mg0.03Si3.92O19.96 and Al8.28Fe0.20Si3.5...

We study the transformation that WO3 nanoparticles produced by Flame Spray Pyrolysis undergo when subjected to heating and cooling cycles by means of accurate in-situ XRD and HRTEM investigations supported by atomistic modeling at the level of Density Functional Theory. As-deposited particles, initially in the monoclinic phase, reversibly transform...

Homogeneous and inclusion-free single crystals of 2:1 mullite (Al4.8Si1.2O9.6) grown by the Czochralski technique were examined by X-ray and neutron diffraction methods. The observed diffuse scattering together with the pattern of satellite reflections confirm previously published data and are thus inherent features of the mullite structure. The id...

In Bragg–Brentano powder X-ray diffraction, incompletely filled sample holders result in a significant loss of intensity for diffraction peaks at small 2θ angles due to shadowing of the diffracted beam by the sample holder. This has to be considered in crystal structure refinements for samples with diffraction peaks in the low 2θ range when shifts...

In this work, a simple method is presented to generate hierarchically structured monolithic types of foam with high specific surface areas and good catalytic activities in a one-step process. The materials prepared are platinum- and zinc/platinum-containing hybrid ceramics generated by the pyrolytic conversion of a mixture of a methyl phenyl polysi...

Large crystals of Bi2M4O9 (M = Fe, Ga) were examined by single-crystal neutron diffraction at the Institut Laue Langevin (ILL) in Grenoble. The crystal structures of these bismuth metal oxides are commonly described as mullite-type compounds in space group Pbam. However, up to several hundreds of reflections were observed in both compounds with sig...

Synthetic mullites (Al4+2xSi2-2xO10-x) belong to one of the most important groups of ceramic materials. Their crystal structure consists of chains of edge-sharing AlO6 octahedra interconnected by tetrahedral double chains of TO4 (T = Al, Si) tetrahedra. The occurrence of oxygen vacancies is associated with the formation of triclusters of TO4 groups...

Tetraphenylphosphonium montmorillonite (TPP-MMT) was prepared from an aqueous solution of tetraphenylphosphonium bromide and a bentonite consisting primarily of sodium rich montmorillonite (Na-MMT) together with minor amounts of cristobalite, quartz and nontronite. The original bentonite, the TPP-MMT and mixtures of TPP-MMT with various amounts of...

Flame spray pyrolysis (FSP) is a novel technique for the fabrication of nanostructured catalysts with far-reaching options to control structure and composition even in cases where complex composites need to be prepared. In this study, we took advantage of this technique to synthesize highly dispersed pure and Pd-doped iron oxide nanoparticles and i...

Flame spray pyrolysis (FSP) has been employed for the syntheses of single crystalline WO3 nanoparticles using tungsten precursors with tungsten in usual (+6) and unusual (+4 and 0) oxidation states. The WO3 nanoparticles have been characterized by powder X-ray diffraction and the patterns have been refined using the Rietveld and the Le Bail method...