Elias Carl Johannes Gießelmann

Synthesis of europium aluminates is usually conducted from the binary oxides (EuO/Eu2O3 + Al2O3) at high temperatures alongside a reductive gas for the stabilization of Eu2+. We are reporting on an alternative pathway starting from EuAl2 (cubic Laves phase, MgCu2 type, Fd3̅m), which was oxidized under different conditions. By heating the intermetallic precursor to different temperatures, first amorphous and at higher temperatures highly crystalline products were observed. However, the question of the Eu valence state in the product will immediately arise. Depending on the reaction procedure used both, the di- and trivalent state could be achieved in the reaction with elemental oxygen. EuIIIAlO3 (GdFeO3 type, Pnma) was observed as the sole crystalline product with excess O2 in the powder X-ray diffraction experiments. The differing chemical composition could be explained by the formation of amorphous γ-Al2O3 proven by 27Al solid-state NMR spectroscopy. Oxidizing EuAl2 under controlled conditions yields X-ray pure EuIIAl2O4 (SrAl2O4 type, P21). Surprisingly, annealing of the EuIIIAlO3/amorphous γ-Al2O3 mixture under vacuum led to the formation of EuIIAl2O4, which was investigated in detail. The different oxidation states of the Eu atoms were proven by magnetic measurements, 151Eu Mössbauer spectroscopic investigations, and photoluminescence studies.

Mechanochemical activation of Na _1.2 V ₃ O ₈ induces crystallite size reduction, surface area enhancement, and local structural changes, accelerating Na de/intercalation kinetics.

Mechanochemical activated NaTi ₂ (PO ₄ ) ₃ , a NASICON-type sodium titanium phosphate (NTP), exhibits enhanced sodium intercalation activity. Thus this activation offers great potential for sodium-ion energy storage.

Partial reduction of transition metal oxides via defect engineering is a promising strategy to enhance their electronic and photocatalytic properties. In this study, we systematically explored the mechanochemical reduction of Nb₂O₅ using LiBH₄ and NaBH₄ as reducing agents. Electron paramagnetic resonance (EPR) spectroscopy confirmed a successful partial reduction of the oxide, as seen by the presence of unpaired electrons. Interestingly, larger hydride concentrations did not necessarily enable a higher degree of reduction as large amounts of boron hydrides acted as a buffer material and thus hindered the effective transfer of mechanical energy. Powder X-ray diffraction (PXRD) and ⁷Li solid-state NMR spectroscopy indicated the intercalation of Li⁺ into the Nb₂O₅ lattice. Raman spectroscopy further revealed the increased structural disorder, while optical measurements showed a decreased band gap compared with pristine Nb₂O₅. The partially reduced samples showed significantly enhanced photocatalytic performance for methylene blue degradation relative to the unmodified oxides.

Partial reduction of transition metal oxides via defect engineering is a promising strategy to enhance their electronic and photocatalytic properties. In this study, we systematically explore the mechanochemical reduction of Nb2O5 using LiBH4 and NaBH4 as reducing agents. Electron paramagnetic resonance (EPR) spectroscopy confirms a successful partial reduction of the oxide, as seen by the presence of unpaired electrons. Interestingly, larger hydride concentrations do not necessarily enable a higher degree of reduction as large amounts of the boron hydrides act as a buffer material and thus hinder the effective transfer of mechanical energy. Powder X-ray diffraction (PXRD) and 7Li solid-state NMR spectroscopy indicate the intercalation of Li+ into the Nb2O5 lattice. Raman spectroscopy further reveals the increased structural disorder, while optical measurements show a decreased band gap compared to pristine Nb2O5. The partially reduced samples show significantly enhanced photocatalytic performance for methylene blue degradation relative to the unmodified oxides.

The synthesis of differently substituted polyferrocenylmethylenes (PFM) via ring‐opening transmetalation polymerization (ROTP) is reported. A number of novel, symmetrically and asymmetrically substituted carba[1]magnesocenophanes have been prepared, which were used as precursors and allowed investigations of the influence of different substitution patterns on the PFM polymer properties. The novel carba[1]magnesocenophanes have been fully characterized by ¹ H and ¹³ C{ ¹ H} NMR spectroscopy, and structurally authenticated by single‐crystal X‐ray diffraction (SC‐XRD). The corresponding PFMs were obtained with molecular weights in a range of M _w =1900 g mol ⁻¹ up to 15100 g mol ⁻¹ and corresponding dispersities of Đ =1.48 to 1.81. All PFMs have been fully characterized by ¹ H and ¹³ C{ ¹ H} NMR spectroscopy, as well as by gel permeation chromatography (GPC), thermal gravimetric analysis (TGA) and matrix assisted laser desorption ionization‐time‐of‐flight (MALDI‐ToF) mass spectrometry. Pyrolysis of spyrocyclic substituted PFM resulted in a ceramic yield above 50 %, while the obtained residue was characterized by powder X‐ray diffraction (PXRD).

CaAl₂ was treated via ball milling to investigate the influence of the subsequent oxidation on the activated material. It was shown that a significantly different reaction pathway was observed.

Synthesis, structure and bonding, magnetic, NMR as well as XPS properties of several new ternary aluminum intermetallics are reported.