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Item Open Access Ab initio machine-learning unveils strong anharmonicity in non-Arrhenius self-diffusion of tungsten(2025) Zhang, Xi; Divinski, Sergiy V.; Grabowski, BlazejThe knowledge of diffusion mechanisms in materials is crucial for predicting their high-temperature performance and stability, yet accurately capturing the underlying physics like thermal effects remains challenging. In particular, the origin of the experimentally observed non-Arrhenius diffusion behavior has remained elusive, largely due to the lack of effective computational tools. Here we propose an efficient ab initio framework to compute the Gibbs energy of the transition state in vacancy-mediated diffusion including the relevant thermal excitations at the density-functional-theory level. With the aid of a bespoke machine-learning interatomic potential, the temperature-dependent vacancy formation and migration Gibbs energies of the prototype system body-centered cubic (BCC) tungsten are shown to be strongly affected by anharmonicity. This finding explains the physical origin of the experimentally observed non-Arrhenius behavior of tungsten self-diffusion. A remarkable agreement between the calculated and experimental temperature-dependent self-diffusivity and, in particular, its curvature is revealed. The proposed computational framework is robust and broadly applicable, as evidenced by first tests for a hexagonal close-packed (HCP) multicomponent high-entropy alloy. The successful applications underscore the attainability of an accurate ab initio diffusion database.Item Open Access Influence of In‐doping on the structure and electrochemical performance of compositionally complex garnet‐type solid electrolytes(2025) Alsawaf, Alaa; Karkera, Guruprakash; Diemant, Thomas; Kante, Monaha Veerraju; Schneider, Yannik; Velasco, Leonardo; Bhattacharya, Subramshu S.; Stainer, Florian; Wilkening, Martin; Clemens, Oliver; Janek, Jürgen; Hahn, Horst; Botros, MiriamThe electrochemical instability of electrode active materials as well as the flammability of the organic liquid electrolytes in Li‐ion batteries pose challenges for their safety and long cycle life. Solid electrolytes (SEs) that exhibit high ionic conductivity and a wide electrochemical stability window alleviate these challenges. Garnet‐type Li7La3Zr2O12 is a promising SE for next‐generation all‐solid‐state batteries. Herein, samples are prepared via a modified solid‐state reaction of compositionally complex Li6.3+zLa3Zr1.1-z Nb0.8Gd0.1InzO12 under different sintering atmospheres. X-ray diffraction patterns and Raman spectra prove the formation of a cubic garnet structure. Significant morphological changes are detected upon In‐doping and correlated to the ionic conductivity. The total Li‐ion conductivity of the dense pellets reaches 1 mS cm-1, among the highest reported to date, with an activation energy of 0.38 eV for the macroscopic ion transport obtained by impedance spectroscopy and as low as 0.24 eV for local Li‐ion hopping processes determined by 7Li nuclear magnetic resonance spin‐lattice relaxation measurements. The electronic contribution to the conductivity is negligible (10-10 S cm-1) making this compositionally complex SE a suitable candidate for all‐solid‐state battery applications.Item Open Access Towards recycling of all‐solid‐state batteries with argyrodite sulfide electrolytes : insights into electrolyte and electrode degradation in dissolution‐based separation processes(2025) Wissel, Kerstin; Hu, Zian; Wu, Xuebin; Jacob, Martine; Küster, Kathrin; Starke, Ulrich; Clemens, OliverAll‐solid‐state Li‐ion batteries (ASSBs) represent a promising leap forward in battery technology, rapidly advancing in development. Among the various solid electrolytes, argyrodite thiophosphates Li6PS5X (X=Cl, Br, I) stand out due to their high ionic conductivity, structural flexibility, and compatibility with a range of electrode materials, making them ideal candidates for efficient and scalable battery applications. However, despite significant performance advancements, the sustainability and recycling of ASSBs remain underexplored, posing a critical challenge for achieving efficient circular processes. This study investigates the dissolution‐based separation and recovery of argyrodite thiophosphate electrolytes and transition metal oxide electrode materials as a potential recycling strategy for ASSBs. A focus is set on the impact of solvent treatments on the recrystallization behavior of these electrolytes. Furthermore, the interactions between dissolved argyrodite thiophosphates and various transition metal oxide electrode materials (LiCoO2, LiMn2O4, LiNi0.8Mn0.1Co0.1O2, LiFePO4 and Li4Ti5O12) is examined to assess their influence on the functional properties of both the electrolytes and electrode materials. Structural, compositional and morphological changes are analyzed using X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, inductively coupled plasma mass spectrometry and X‐ray photoelectron spectroscopy. Our findings provide insights into the complexities of recycling ASSBs, but also highlight the potential for developing efficient, sustainable recycling processes.Item Open Access Free-energy perturbation in the exchange-correlation space accelerated by machine learning : application to silica polymorphs(2025) Forslund, Axel; Jung, Jong Hyun; Ikeda, Yuji; Grabowski, BlazejWe propose a free-energy-perturbation approach accelerated by machine-learning potentials to efficiently compute transition temperatures and entropies for all rungs of Jacob’s ladder. We apply the approach to the dynamically stabilized phases of SiO2, which are characterized by challengingly small transition entropies. All investigated functionals from rungs 1-4 fail to predict an accurate transition temperature by 25-200%. Only by ascending to the fifth rung, within the random phase approximation, an accurate prediction is possible, giving a relative error of 5%. We provide a clear-cut procedure and relevant data to the community for, e.g., developing and evaluating new functionals.Item Open Access Floating zone growth of large tetragonal Ruddlesden-Popper bilayer nickelate YySr3-yNi2-xAlxO7-δ single crystals(2025) Yilmaz, Hasan; Sosa-Lizama, Pablo; Knauft, Manuel; Küster, Kathrin; Starke, Ulrich; Isobe, Masahiko; Clemens, Oliver; Aken, Peter A. van ; Suyolcu, Y. E.; Puphal, PascalThe discovery of superconductivity under high pressure in Ruddlesden-Popper (RP) type phase bilayer La3Ni22.5+O7 and trilayer La4Ni32.66+O10 has initiated the frontier of nickelate-based superconductors. In this context, RP-type phases within the Sr-Ni-O system offer promising alternatives as they offer unconventional high oxidation states and Sr-T-O comprises the usual RP series. Here, the intrinsic stability of the undoped Sr-Ni-O framework is investigated using density functional theory (DFT). While Sr3Ni2O7 (SNO) is stable synthesis so far requires Al co-substition in Sr3Ni2-xAlxO7-δ (SNAO). Y-doping resulting in YySr3-yNi2-xAlxO7-δ (YSNAO) effectively mitigates the challenge posed by an insulating ground state. This modification yields a substantial reduction in resistivity, with the crystals exhibiting semiconducting behavior. To explore phase formation within the narrow compositional window of the Y-Sr-Ni-Al-O system, single crystals were grown using the optical floating zone (OFZ) technique under an oxygen partial pressure of approximately 10 bar. The optimized growth conditions for YSNAO enabled the production of large (6 × 5 x 3 mm3), high-quality crystals suitable for neutron scattering experiments. In the absence of Al, crystal growth yielded the n = 1 RP phase Sr1.66Y0.33NiO4-δ, for which single crystals were obtained. The structural, chemical, electrical, and magnetic properties of both the as-grown and topochemically reduced YSNAO compounds were comprehensively characterized through diffraction, spectroscopy, transport, and magnetization measurements.