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- ItemDesign of high-performance antimony/MXene hybrid electrodes for sodium-ion batteries(London [u.a.] : RSC, 2022) Arnold, Stefanie; Gentile, Antonio; Li, Yunjie; Wang, Qingsong; Marchionna, Stefano; Ruffo, Riccardo; Presser, VolkerDue to their versatile properties and excellent electrical conductivity, MXenes have become attractive materials for alkali metal-ion batteries. However, as the capacity is limited to lower values due to the intercalation mechanism, these materials can hardly keep up in the ever-fast-growing community of battery research. Antimony has a promisingly high theoretical sodiation capacity characterized by an alloying reaction. The main drawback of this type of battery material is related to the high volume changes during cycling, often leading to electrode cracking and pulverization, resulting in poor electrochemical performance. A synergistic effect of combing antimony and MXene can be expected to obtain an optimized electrochemical system to overcome capacity fading of antimony while taking advantage of MXene charge storage ability. In this work, variation of the synthesis parameters and material design strategy have been dedicated to achieving the optimized antimony/MXene hybrid electrodes for high-performance sodium-ion batteries. The optimized performance does not align with the highest amount of antimony, the smallest nanoparticles, or the largest interlayer distance of MXene but with the most homogeneous distribution of antimony and MXene while both components remain electrochemically addressable. As a result, the electrode with 40 mass% MXene, not previously expanded, etched with 5 mass% HF and 60% antimony synthesized on the surfaces of MXene emerged as the best electrode. We obtained a high reversible capacity of 450 mA h g−1 at 0.1 A g−1 with a capacity retention of around 96% after 100 cycles with this hybrid material. Besides the successful cycling stability, this material also exhibits high rate capability with a capacity of 365 mA h g−1 at 4 A g−1. In situ XRD measurements and post mortem analysis were used to investigate the reaction mechanism.
- ItemThe influence of Sb doping on the local structure and disorder in thermoelectric ZnO:Sb thin films(Lausanne : Elsevier, 2023) Ribeiro, Joana M.; Rodrigues, Frederico J.; Correia, Filipe C.; Pudza, Inga; Kuzmin, Alexei; Kalinko, Aleksandr; Welter, Edmund; Barradas, Nuno P.; Alves, Eduardo; LaGrow, Alec P.; Bondarchuk, Oleksandr; Welle, Alexander; Telfah, Ahmad; Tavares, Carlos J.Thermoelectric transparent ZnO:Sb thin films were deposited by magnetron sputtering, with Sb content varying between 2 and 14 at%. As evidenced by X-ray diffraction analysis, the films crystallize in the ZnO wurtzite structure for lower levels of Sb-doping, developing a degree of amorphization for higher levels of Sb-doping. Temperature-dependent (10–300 K) X-ray absorption spectroscopy studies of the produced thin films were performed at the Zn and Sb K-edges to shed light on the influence of Sb doping on the local atomic structure and disorder in the ZnO:Sb thin films. The analysis of the Zn K-edge EXAFS spectra by the reverse Monte Carlo method allowed to extract detailed and accurate structural information in terms of the radial and bond angle distribution functions. The obtained results suggest that the introduction of antimony to the ZnO matrix promotes static disorder, which leads to partial amorphization with very small crystallites (∼3 nm) for large (12–14 at%) Sb content. Rutherford backscattering spectrometry (RBS) experiments enabled the determination of the in-depth atomic composition profiles of the films. The film composition at the surfaces determined by X-ray photoelectron spectroscopy (XPS) matches that of the bulk determined by RBS, except for higher Sb-doping in ZnO films, where the concentration of oxygen determined by XPS is smaller near the surface, possibly due to the formation of oxygen vacancies that lead to an increase in electrical conductivity. Traces of Sb–Sb metal bonds were found by XPS for the sample with the highest level of Sb-doping. Time-of-flight secondary ion mass spectrometry obtained an Sb/Zn ratio that follows that of the film bulk determined by RBS, although Sb is not always homogeneous, with samples with smaller Sb content (2 and 4 at% of Sb) showing a larger Sb content closer to the film/substrate interface. From the optical transmittance and reflectance curves, it was determined that the films with the lower amount of Sb doping have larger optical band-gaps, in the range of 2.9–3.2 eV, while the partially amorphous films with higher Sb content have smaller band-gaps in the range of 1.6–2.1 eV. Albeit the short-range crystalline order (∼3 nm), the film with 12 at% of Sb has the highest absolute Seebeck coefficient (∼56 μV/K) and a corresponding thermoelectric power factor of ∼0.2 μW·K−2·m−1.
- ItemEpitaxial stannate pyrochlore thin films: Limitations of cation stoichiometry and electron doping(Melville, NY : AIP Publishing, 2021) Hensling, Felix V. E.; Dahliah, Diana; Dulal, Prabin; Singleton, Patrick; Sun, Jiaxin; Schubert, Jürgen; Paik, Hanjong; Subedi, Indra; Subedi, Biwas; Rignanese, Gian-Marco; Podraza, Nikolas J.; Hautier, Geoffroy; Schlom, Darrell G.We have studied the growth of epitaxial films of stannate pyrochlores with a general formula A2Sn2O7 (A = La and Y) and find that it is possible to incorporate ∼25% excess of the A-site constituent; in contrast, any tin excess is expelled. We unravel the defect chemistry, allowing for the incorporation of excess A-site species and the mechanism behind the tin expulsion. An A-site surplus is manifested by a shift in the film diffraction peaks, and the expulsion of tin is apparent from the surface morphology of the film. In an attempt to increase La2Sn2O7 conductivity through n-type doping, substantial quantities of tin have been substituted by antimony while maintaining good film quality. The sample remained insulating as explained by first-principles computations, showing that both the oxygen vacancy and antimony-on-tin substitutional defects are deep. Similar conclusions are drawn on Y2Sn2O7. An alternative n-type dopant, fluorine on oxygen, is shallow according to computations and more likely to lead to electrical conductivity. The bandgaps of stoichiometric La2Sn2O7 and Y2Sn2O7 films were determined by spectroscopic ellipsometry to be 4.2 eV and 4.48 eV, respectively. © 2021 Author(s).
- ItemResearch Update: Van-der-Waals epitaxy of layered chalcogenide Sb2Te3 thin films grown by pulsed laser deposition(Melville, NY : AIP Publ., 2017) Hilmi, Isom; Lotnyk, Andriy; Gerlach, Jürgen W.; Schumacher, Philipp; Rauschenbach, BerndAn attempt to deposit a high quality epitaxial thin film of a two-dimensionally bonded (layered) chalcogenide material with van-der-Waals (vdW) epitaxy is of strong interest for non-volatile memory application. In this paper, the epitaxial growth of an exemplary layered chalcogenide material, i.e., stoichiometric Sb2Te3 thin films, is reported. The films were produced on unreconstructed highly lattice-mismatched Si(111) substrates by pulsed laser deposition (PLD). The films were grown by vdW epitaxy in a two-dimensional mode. X-ray diffraction measurements and transmission electron microscopy revealed that the films possess a trigonal Sb2Te3 structure. The single atomic Sb/Te termination layer on the Si surface was formed initializing the thin film growth. This work demonstrates a straightforward method to deposit vdW-epitaxial layered chalcogenides and, at the same time, opens up the feasibility to fabricate chalcogenide vdW heterostructures by PLD.