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- ItemSyntheses, crystal structure and magnetic properties of Tl9RETe6 (RE = Ce, Sm, Gd)(Basel : MDPI AG, 2020) Isaeva, A.; Schönemann, R.; Doert, T.The three compounds Tl9RETe6 with RE = Ce, Sm, Gd were synthesized from the elements at 1020 K. Their isostructural crystal structures are ordered derivatives of the Tl5Te3 type with rare-earth metal and thallium occupying different Wyckoff positions. The structures can be understood as charge-ordered in accordance with the Zintl-Klemm concept: 9 Tl+ + RE3+ + 6 Te2-. DFT calculations for Tl9GdTe6, however, result in a low, but finite density of states at the Fermi level. Magnetic data confirm trivalent Gd, but indicate a small amount of Ce4+ in Tl9CeTe6; no indications for long-range magnetic order was found down to T = 2 K.
- ItemStabilizing a three-center single-electron metal–metal bond in a fullerene cage(Cambridge : RSC, 2021) Jin, Fei; Xin, Jinpeng; Guan, Runnan; Xie, Xiao-Ming; Chen, Muqing; Zhang, Qianyan; Popov, Alexey A.; Xie, Su-Yuan; Yang, ShangfengTrimetallic carbide clusterfullerenes (TCCFs) encapsulating a quinary M3C2 cluster represent a special family of endohedral fullerenes with an open-shell electronic configuration. Herein, a novel TCCF based on a medium-sized rare earth metal, dysprosium (Dy), is synthesized for the first time. The molecular structure of Dy3C2@Ih(7)-C80 determined by single crystal X-ray diffraction shows that the encapsulated Dy3C2 cluster adopts a bat ray configuration, in which the acetylide unit C2 is elevated above the Dy3 plane by ∼1.66 Å, while Dy–Dy distances are ∼3.4 Å. DFT computational analysis of the electronic structure reveals that the endohedral cluster has an unusual formal charge distribution of (Dy3)8+(C2)2−@C806− and features an unprecedented three-center single-electron Dy–Dy–Dy bond, which has never been reported for lanthanide compounds. Moreover, this electronic structure is different from that of the analogous Sc3C2@Ih(7)-C80 with a (Sc3)9+(C2)3−@C806− charge distribution and no metal–metal bonding.
- ItemPhase equilibria in the Gd–Cr–Ge system at 1070 K(Ivano-Frankivsʹk : Fizyko-chimičnyj instytut DVNZ "Prykarpatsʹkyj nacionalʹnyj universytet imeni Vasylja Stefanyka", 2021) Konyk, M.; Romaka, L.; Stadnyk, Yu.; Romaka, V.V.; Pashkevych, V.The isothermal section of the phase diagram of the Gd–Cr–Ge ternary system was constructed at 1070 K over the whole concentration range using X-ray diffractometry, metallography and electron microprobe (EPM) analysis. Three ternary compounds are realized in the Gd–Cr–Ge system at the temperature of annealing: Gd117Cr52Ge112 (Tb117Fe52Ge112 structure type, space group Fm-3m, Pearson symbol cF1124, a = 2.8971(6) nm), GdCr6Ge6 (SmMn6Sn6 structure type, space group P6/mmm, Pearson symbol hP16, a = 0.51797(2), c = 0.82901(4) nm) and GdCr1-хGe2 (CeNiSi2 structure type, space group Cmcm, Pearson symbol oS16, a = 0.41569(1)-0.41593(8), b = 1.60895(6)-1.60738(3), c = 0.40318(1)-0.40305(8) nm). For the GdCr1-xGe2 compound the homogeneity range was determined (x=0.73 – 0,69).
- ItemTiNb2O7 and VNB9O25 of ReO3 type in hybrid Mg−Li batteries: Electrochemical and interfacial insights(Washington, DC : American Chemical Society, 2020) Maletti, Sebastian; Herzog-Arbeitman, Abraham; Oswald, Steffen; Senyshyn, Anatoliy; Giebeler, Lars; Mikhailova, DariaAs one of the beyond-lithium battery concepts, hybrid metal-ion batteries have aroused growing interest. Here, TiNb2O7 (TNO) and VNb9O25 (VNO) materials were prepared using a high-temperature solid-state synthesis and, for the first time, comprehensively examined in hybrid Mg−Li batteries. Both materials adopt ReO3-related structures differing in the interconnection of oxygen polyhedra and the resulting guest ion diffusion paths. We show applicability of the compounds in hybrid cells providing capacities comparable to those reached in Li-ion batteries (LIBs) at room temperature (220 mAh g−1 for TNO and 150 mAh g−1 for VNO, both at 0.1 C), their operability in the temperature range between −10 and 60 °C, and even better capacity retention than in pure LIBs, rendering this hybrid technology superior for long-term application. Post mortem X-ray photoelectron spectroscopy reveals a cathode−electrolyte interface as a key ingredient for providing excellent electrochemical stability of the hybrid battery. A significant contribution of the intercalation pseudocapacitance to charge storage was observed for both materials in Li- and Mg−Li batteries. However, the pseudocapacitive part is higher for TNO than for VNO, which correlates with structural distinctions, providing better accessibility of diffusion pathways for guest cations in TNO and, as a consequence, a higher ionic transport within the crystal structure. © 2020 American Chemical Society
- ItemRemarkable performance recovery in highly defective perovskite solar cells by photo-oxidation(London [u.a.] : RSC, 2023) Goetz, Katelyn P.; Thome, Fabian T. F.; An, Qingzhi; Hofstetter, Yvonne J.; Schramm, Tim; Yangui, Aymen; Kiligaridis, Alexander; Loeffler, Markus; Taylor, Alexander D.; Scheblykin, Ivan G.; Vaynzof, YanaExposure to environmental factors is generally expected to cause degradation in perovskite films and solar cells. Herein, we show that films with certain defect profiles can display the opposite effect, healing upon exposure to oxygen under illumination. We tune the iodine content of methylammonium lead triiodide perovskite from understoichiometric to overstoichiometric and expose them to oxygen and light prior to the addition of the top layers of the device, thereby examining the defect dependence of their photooxidative response in the absence of storage-related chemical processes. The contrast between the photovoltaic properties of the cells with different defects is stark. Understoichiometric samples indeed degrade, demonstrating performance at 33% of their untreated counterparts, while stoichiometric samples maintain their performance levels. Surprisingly, overstoichiometric samples, which show low current density and strong reverse hysteresis when untreated, heal to maximum performance levels (the same as untreated, stoichiometric samples) upon the photooxidative treatment. A similar, albeit smaller-scale, effect is observed for triple cation and methylammonium-free compositions, demonstrating the general application of this treatment to state-of-the-art compositions. We examine the reasons behind this response by a suite of characterization techniques, finding that the performance changes coincide with microstructural decay at the crystal surface, reorientation of the bulk crystal structure for the understoichiometric cells, and a decrease in the iodine-to-lead ratio of all films. These results indicate that defect engineering is a powerful tool to manipulate the stability of perovskite solar cells.
- ItemCharting lattice thermal conductivity for inorganic crystals and discovering rare earth chalcogenides for thermoelectrics(Cambridge : RSC Publ., 2021) Zhu, Taishan; He, Ran; Gong, Sheng; Xie, Tian; Gorai, Prashun; Nielsch, Kornelius; Grossman, Jeffrey C.Thermoelectric power generation represents a promising approach to utilize waste heat. The most effective thermoelectric materials exhibit low thermal conductivity κ. However, less than 5% out of about 105 synthesized inorganic materials are documented with their κ values, while for the remaining 95% κ values are missing and challenging to predict. In this work, by combining graph neural networks and random forest approaches, we predict the thermal conductivity of all known inorganic materials in the Inorganic Crystal Structure Database, and chart the structural chemistry of κ into extended van-Arkel triangles. Together with the newly developed κ map and our theoretical tool, we identify rare-earth chalcogenides as promising candidates, of which we measured ZT exceeding 1.0. We note that the κ chart can be further explored, and our computational and analytical tools are applicable generally for materials informatics.
- ItemComprehensive scan for nonmagnetic Weyl semimetals with nonlinear optical response(London : Nature Publishing Group, 2020) Xu, Q.; Zhang, Y.; Koepernik, K.; Shi, W.; van den Brink, J.; Felser, C.; Sun, Y.First-principles calculations have recently been used to develop comprehensive databases of nonmagnetic topological materials that are protected by time-reversal or crystalline symmetry. However, owing to the low symmetry requirement of Weyl points, a symmetry-based approach to identifying topological states cannot be applied to Weyl semimetals (WSMs). To date, WSMs with Weyl points in arbitrary positions are absent from the well-known databases. In this work, we develop an efficient algorithm to search for Weyl points automatically and establish a database of nonmagnetic WSMs with Weyl points near the Fermi level based on the experimental non-centrosymmetric crystal structures in the Inorganic Crystal Structure Database (ICSD). In total, 46 Weyl semimetals were discovered to have nearly clean Fermi surfaces and Weyl points within 300 meV of the Fermi level. Nine of them are chiral structures which may exhibit the quantized circular photogalvanic effect. In addition, the nonlinear optical response is studied and the giant shift current is explored. Besides nonmagnetic WSMs, our powerful tools can also be used in the discovery of magnetic topological materials.
- ItemAnisotropic fractal magnetic domain pattern in bulk Mn1.4PtSn(Woodbury, NY : Inst., 2020) Sukhanov, A.S.; Zuniga Cespedes, B.E.; Vir, P.; Cameron, A.S.; Heinemann, A.; Martin, N.; Chaboussant, G.; Kumar, V.; Milde, P.; Eng, L.M.; Felser, C.; Inosov, D.S.The tetragonal compound Mn1.4PtSn with D2d symmetry recently attracted attention as the first known material that hosts magnetic antiskyrmions, which differ from the skyrmions known so far by their internal structure. The latter have been found in a number of magnets with the chiral crystal structure. In previous works, the existence of antiskyrmions in Mn1.4PtSn was unambiguously demonstrated in real space by means of Lorentz transmission electron microscopy on thin-plate samples (∼100 nm thick). In the present study, we used small-angle neutron scattering and magnetic force microscopy to perform reciprocal- and real-space imaging of the magnetic texture of bulk Mn1.4PtSn single crystals at different temperatures and in applied magnetic field. We found that the magnetic texture in the bulk differs significantly from that of thin-plate samples. Instead of spin helices or an antiskyrmion lattice, we observe an anisotropic fractal magnetic pattern of closure domains in zero field above the spin-reorientation transition temperature, which transforms into a set of bubble domains in high field. Below the spin-reorientation transition temperature the strong in-plane anisotropy as well as the fractal self-affinity in zero field is gradually lost, while the formation of bubble domains in high field remains robust. The results of our study highlight the importance of dipole-dipole interactions in thin-plate samples for the stabilization of antiskyrmions and identify criteria which should guide the search for potential (anti)skyrmion host materials. Moreover, they provide consistent interpretations of the previously reported magnetotransport anomalies of the bulk crystals. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.