Technische Universität Darmstadt

The anal. of exptl. results with Python often requires writing many code scripts which all need access to the same set of functions.In a common field of research, this set will be nearly the same for many users.The qspec Python package was developed to provide functions for phys. formulas, simulations and data anal. routines widely used in laser spectroscopy and related fields.Most functions are compatible with numpy arrays, enabling fast calculations with large samples of data.A multidimensional linear regression algorithm enables a King plot analyses over multiple at. transitions.A modular framework for constructing lineshape models can be used to fit large sets of spectroscopy data.A simulation module within the package provides user-friendly methods to simulate the coherent time-evolution of atoms in electro-magnetic fields without the need to explicitly derive a Hamiltonian.

The correct description of the kinetics of NH₃ oxidation over Pt is crucial for the optimal catalyst design.Despite a general agreement on the elementary steps, major discrepancies on the value of the activation energy are still present, with exptl. studies showing activation energies > 100 kJ/mol, way above the activation energies predicted by DFT (typically around 50 kJ/mol ).In this work, we apply a novel kinetic anal., reconciling exptl. and theor. derived activation energies.We developed a Transient Response Measurement protocol which allowed to measure the intrinsic kinetics, observing an activation energy of 39 kJ/mol, close to theory, and then the following Pt oxide formation/decompositionBy combining the two phenomena, we obtained a model describing the exptl. light-off curves and their high apparent activation energy (>100 kJ/mol).This is explained by the Pt-oxide decomposition evolving concurrently with the heating ramp, leading to a gradual enhancement of the catalytic activity beyond the increase related to the low intrinsic activation energy.Furthermore, our model explains previously observed effects like the NH₃ conversion hysteresis during light-up/light-down, and the O₂ inhibition on NH₃ light-off.The work paves the way for a more fundamental understanding of a wide range of NH₃ conversion/abatement catalytic systems.

Cationic redistribution in spinel ferrite systems greatly influences the magnetic ordering and the associated phenomena. Here, the effect of the synthesis condition on the cationic redistribution and its correlation with the magnetic properties were explored in the Cu2+ substituted ZnFe2O4 spinel ferrite. X-ray photoelectron spectroscopy and x-ray diffraction studies reveal that the variation of sintering temperature redistributes the cations between tetrahedral and octahedral sublattices. Results from low field dc-magnetic susceptibility measurements show that the susceptibility increases with decreasing sintering temperature of the sample. Furthermore, the ac-susceptibility results suggest that the sample sintered at 1048 K (1148 K) exhibits spin-glass behavior with a glass transition temperature of ∼49.2 K (47.1 K) and a cluster-glass behavior at a higher temperature of ∼317 K (330 K), characteristics that are absent in the sample sintered at 1248 K. The sample annealed at 1048 K exhibits a magnetocaloric effect with a maximum isothermal entropy change of ∼1.21 J kg−1 K−1 at μ0H=5 T.