2022, Oswald, Steffen

Li-based batteries are a key element in reaching a sustainable energy economy in the near future. The understanding of the very complex electrochemical processes is necessary for the optimization of their performance. X-ray photoelectron spectroscopy (XPS) is an accepted method used to improve understanding around the chemical processes at the electrode surfaces. Nevertheless, its application is limited because the surfaces under investigation are mostly rough and inhomogeneous. Local elemental analysis, such as Auger electron spectroscopy (AES), could assist XPS to gain more insight into the chemical processes at the surfaces. In this paper, some challenges in using electron spectroscopy are discussed, such as binding energy (BE) referencing for the quantitative study of chemical shifts, gas atmospheric influences, or beam damage (including both AE and XP spectroscopy). Carefully prepared and surface-modified metallic lithium material is used as model surface, considering that Li is the key element for most battery applications.

2022, Ciobanu, Vladimir, Ursaki, Veaceslav V., Lehmann, Sebastian, Braniste, Tudor, Raevschi, Simion, Zalamai, Victor V., Monaico, Eduard V., Colpo, Pascal, Nielsch, Kornelius, Tiginyanu, Ion M.

In this paper, new aeromaterials are proposed on the basis of titania thin films deposited using atomic layer deposition (ALD) on a sacrificial network of ZnO microtetrapods. The technology consists of two technological steps applied after ALD, namely, thermal treatment at different temperatures and etching of the sacrificial template. Two procedures are applied for etching, one of which is wet etching in a citric acid aqua solution, while the other one is etching in a hydride vapor phase epitaxy (HVPE) system with HCl and hydrogen chemicals. The morphology, composition, and crystal structure of the produced aeromaterials are investigated depending on the temperature of annealing and the sequence of the technological steps. The performed photoluminescence analysis suggests that the developed aeromaterials are potential candidates for photocatalytic applications.

2024, Roslova, Maria, Büchner, Bernd, Maljuk, Andrey

In this review, we summarize recent progress in crystal growth and understanding of the influence of crystal structure on superconductivity in pure and Pb-doped Bi2Sr2CuOy (Bi-2201) materials belonging to the overdoped region of high-temperature cuprate superconductors. The crystal growth of Bi-2201 superconductors faces challenges due to intricate materials chemistry and the lack of knowledge of corresponding phase diagrams. Historically, a crucible-free floating zone method emerged as the most promising growth approach for these materials, resulting in high-quality single crystals. This review outlines the described methods in the literature and the authors’ synthesis endeavors encompassing Pb-doped Bi-2201 crystals, provides a detailed structural characterization of as-grown and post-growth annealed samples, and highlights optimal growth conditions that yield large-size, single-phase, and compositionally homogeneous Bi-2201 single crystals.

2023, Elmroth Nordlander, Jonas, Bermeo, Marie, Ternero, Pau, Wahlqvist, David, Schmeida, Toni, Blomberg, Sara, Messing, Maria E., Ek, Martin, Hübner, Julia-Maria

Spark ablation is an advantageous method for the generation of metallic nanoparticles with defined particle sizes and compositions. The reaction of the metal particles with the carrier gas during the synthesis and, therefore, the incorporation of those light elements into structural voids or even compound formation was confirmed for hydrides and oxides but has only been suspected to occur for nitrides. In this study, dispersed nanoparticles of Mo3Ni2N and Mo with Janus morphology, and defined particle sizes were obtained by spark discharge generation as a result of carrier gas ionization and characterized using transmission electron microscopy and powder X-ray diffraction. Metal nitrides possess beneficial catalytic and thermoelectric properties, as well as high hardness and wear resistance. Therefore, this method offers the possibility of controlled synthesis of materials which are interesting for numerous applications.

2022, Ćwik, Jacek, Koshkid’ko, Yurii, Nenkov, Konstantin, Tereshina-Chitrova, Evgenia, Weise, Bruno, Kowalska, Karolina

In this paper, the results of heat capacity measurements performed on the polycrystalline Tb1-xErxNi2 intermetallic compounds with x = 0.25, 0.5 and 0.75 are presented. The Debye temperatures and lattice contributions as well as the magnetic part of the heat capacity were determined and analyzed. The heat capacity measurements reveal that the substitution of Tb atoms for Er atoms leads to a linear reduction of the Curie temperatures in the investigated compounds. The ordering temperatures decrease from 28.3 K for Tb0.25Er0.75Ni2 to 12.9 K for Tb0.75Er0.25Ni2. Heat capacity measurements enabled us to calculate with good approximation the isothermal magnetic entropy ΔSmag and adiabatic temperature changes ΔTad for Tb1-xErxNi2, for the magnetic field value equal to 1 T and 2 T. The optimal molar ratios of individual Tb0.75Er0.25Ni2, Tb0.5Er0.5Ni2 and Tb0.25Er0.75Ni2 components in the final composite were theoretically determined. According to the obtained results, the investigated composites make promising candidates that can find their application as an active body in a magnetic refrigerator performing an Ericsson cycle at low temperatures. Moreover, for the Tb0.5Er0.5Ni2 compound, direct measurements of adiabatic temperature change in the vicinity of the Curie temperature in the magnetic field up to 14 T were performed. The obtained high-field results are compared to the data for the parent TbNi2 and ErNi2 compounds, and their magnetocaloric properties near the Curie temperature are analyzed in the framework of the Landau theory for the second-order phase transitions.

2022, Voloshyna, Olesia, Romaka, Vitaliy V., Karmakar, Koushik ;Seiro, Silvia, Maljuk, Andrey, Büchner, Bernd

The travelling solvent floating zone (TSFZ) growth of Eu-substituted LSCO (La1.81−xEuxSr0.19CuO4, with nominal x = 0 ÷ 0.4) single crystals was systematically explored for the first time. The substitution of La with Eu considerably decreased the decomposition temperature. Optimal growth parameters were found to be: oxygen pressure 9.0–9.5 bars; Eu-free CuO-poor solvent (66 mol% CuO) with a molar ratio of La2O3:SrCO3:CuO = 4:4.5:16.5 and growth rate 0.6 mm/hour. The obtained single crystals were characterized with optical polarized microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy analysis. The solubility of Eu in LSCO appeared to be limited to x~0.36–0.38 under the used conditions. The substitution of La3+ with smaller Eu3+ ions led to a structural transition from tetragonal with space group I4/mmm for La1.81Sr0.19CuO4 (x = 0) to orthorhombic with space group Fmmm for La1.81−xSr0.19EuxCuO4 (x = 0.2, 0.3, 0.4), and to a substantial shrinking of the c-axis from 13.2446 Å (x = 0.0) to 13.1257 Å (x = 0.4). Such structural changes were accompanied by a dramatic decrease in the superconducting critical temperature, Tc, from 29.5 K for x = 0 to 13.8 K for 0.2. For x ≥ 0.3, no superconductivity was detected down to 4 K.

2022, Pavlenko, Maksim A., Di Rino, Franco, Boron, Leo, Kondovych, Svitlana, Sené, Anaïs, Tikhonov, Yuri A., Razumnaya, Anna G., Vinokur, Valerii M., Sepliarsky, Marcelo, Lukyanchuk, Igor A.

Ferroelectric materials manifest unique dielectric, ferroelastic, and piezoelectric properties. A targeted design of ferroelectrics at the nanoscale is not only of fundamental appeal but holds the highest potential for applications. Compared to two-dimensional nanostructures such as thin films and superlattices, one-dimensional ferroelectric nanowires are investigated to a much lesser extent. Here, we reveal a variety of the topological polarization states, particularly the vortex and helical chiral phases, in loaded ferroelectric nanowires, which enable us to complete the strain–temperature phase diagram of the one-dimensional ferroelectrics. These phases are of prime importance for optoelectronics and quantum communication technologies

2022, Ursaki, Veaceslav V., Lehmann, Sebastian, Zalamai, Victor V., Morari, Vadim, Nielsch, Kornelius, Tiginyanu, Ion M., Monaico, Eduard V.

GaAs nanowire arrays have been prepared by anodization of GaAs substrates. The nanowires produced on (111)B GaAs substrates were found to be oriented predominantly perpendicular to the substrate surface. The prepared nanowire arrays have been coated with thin ZnO or TiO2 layers by means of thermal atomic layer deposition (ALD), thus coaxial core–shell hybrid structures are being fabricated. The hybrid structures have been characterized by scanning electron microscopy (SEM) for the morphology investigations, by Energy Dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis for the composition and crystal structure assessment, and by photoluminescence (PL) spectroscopy for obtaining an insight on emission polarization related to different recombination channels in the prepared core–shell structures.

2023, Voloshyna, Olesia, Gorbunov, Mikhail V., Mikhailova, Daria, Maljuk, Andrey, Seiro, Silvia, Büchner, Bernd

The flux growth of InVO4 bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V2O5:InVO4 = 1:1 could not be used as a self-flux since no sign of melting was observed up to 1100 °C. Crystals of InVO4 of typical size 0.5 × 1 × 7 mm3 were obtained using copper pyrovanadate (Cu2V2O7) as a flux, using Pt crucibles. X-ray powder diffraction confirmed the orthorhombic Cmcm structure. Rests of the flux material were observed on the sample surface, with occasional traces of Pt indicating some level of reaction with the crucible. X-ray absorption spectroscopy showed that oxidation states of indium and vanadium ions are +3 and +5, respectively. The size and high quality of the obtained InVO4 crystals makes them excellent candidates for further study of their physical properties.

2022, Shipulin, Ilya A., Thomas, Aleena Anna, Holleis, Sigrid, Eisterer, Michael, Nielsch, Kornelius, Hühne, Ruben

We report the local structural and superconducting properties of undoped and Ag-doped YBa2Cu3O6+x (YBCO) films with a thickness of up to 1 µm prepared by pulsed laser deposition on SrTiO3 (STO) single crystals and on ion-beam-assisted deposition (IBAD) and rolling-assisted biaxially textured substrate (RABiTS)-based metal templates. X-ray diffraction demonstrates the high crystalline quality of the films on both single crystalline substrates and metal-based templates, respectively. Although there was only a slight decrease in Tc of up to 1.5 K for the Ag-doped YBCO films on all substrates, we found significant changes in their transport characteristics. The effect of the silver doping mainly depended on the concentration of silver, the type of substrate, and the temperature and magnetic field. In general, the greatest improvement in Jc over a wide range of magnetic fields and temperatures was observed for the 5%Ag-doped YBCO films on STO substrates, showing a significant increase compared to undoped films. Furthermore, a slight Jc improvement was observed for the 2%Ag-doped YBCO films on the RABiTS templates at temperatures below 65 K, whereas Jc decreased for the Ag-doped films on IBAD-MgO-based templates compared to undoped YBCO films. Using detailed electron microscopy studies, small changes in the local microstructure of the Ag-doped YBCO films were revealed; however, no clear correlation was found with the transport properties of the films.