Superconductivity–Electron Count Relationship in Heusler Phasesthe Case of LiPd₂Si

We report superconductivity in the full Heusler compound LiPd2Si (space group Fm3̅m, No. 225) at a critical temperature of Tc = 1.3 K and a normalized heat capacity jump at Tc, ΔC/γTc = 1.1. The low-temperature isothermal magnetization curves imply type-I superconductivity, as previously observed in LiPd2Ge. We show, based on density functional theory calculations and using the molecular orbital theory approach, that while LiPd2Si and LiPd2Ge share the Pd cubic cage motif that is found in most of the reported Heusler superconductors, they show distinctive features in the electronic structure. This is due to the fact that Li occupies the site which, in other compounds, is filled with an early transition metal or a rare-earth metal. Thus, while a simple valence electron count–property relationship is useful in predicting and tuning Heusler materials, inclusion of the symmetry of interacting frontier orbitals is also necessary for the best understanding

Ternary Bismuthide SrPtBi₂: Computation and Experiment in Synergism to Explore Solid-State Materials

A combination of theoretical calculation and the experimental synthesis to explore the new ternary compound is demonstrated in the Sr–Pt–Bi system. Because Pt–Bi is considered as a new critical charge-transfer pair for superconductivity, it inspired us to investigate the Sr–Pt–Bi system. With a thorough calculation of all the known stable/metastable compounds in the Sr–Pt–Bi system and crystal structure predictions, the thermodynamic stability of hypothetical stoichiometry, SrPtBi₂, is determined. Following the high-temperature synthesis and crystallographic analysis, the first ternary bismuthide in Sr–Pt–Bi, SrPtBi₂ was prepared, and the stoichiometry was confirmed experimentally. SrPtBi₂ crystallizes in the space group <i>Pnma</i> (S.G. 62, Pearson Symbol <i>oP48</i>), which matches well with theoretical prediction using an adaptive genetic algorithm. Using first-principles calculations, we demonstrate that the orthorhombic structure has lower formation energies than other 112 structure types, such as tetragonal BaMnBi₂ (CuSmP₂) and LaAuBi₂ (CuHfSi₂) structure types. The bonding analysis indicates that the Pt–Bi interactions play a critical role in structural stability. The physical property measurements show the metallic properties at the low temperature, which agrees with the electronic structure assessment

Photocatalytically Active TiO₂/Ag₂O Nanotube Arrays Interlaced with Silver Nanoparticles Obtained from the One-Step Anodic Oxidation of Ti–Ag Alloys

The development of a photocatalyst with remarkable activity to degrade pollutants in aqueous and gas phase requires visible light-responsive stable materials, easily organized in the form of a thin layer (to exclude the highly expensive separation step). In this work, we present a one-step strategy for synthesizing material in the form of a self-organized TiO₂/Ag₂O nanotube (NT) array interlaced with silver nanoparticles (as in a cake with raisins) that exhibited photoactivity significantly enhanced compared to that of pristine TiO₂ NTs under both ultraviolet (UV) and visible (vis) irradiation. An NT array composed of a mixture of TiO₂ and Ag₂O and spiked with Ag nanoparticles was formed via the anodization of a Ti–Ag alloy in a one-step reaction. Silver NPs have been formed during the <i>in situ</i> generation of Ag ions and were (i) embedded in the NT walls, (ii) stuck on the external NT walls, and (iii) placed inside the NTs. The enhancement of photocatalytic efficiency can be ascribed to the existence of an optimal content of Ag₂O and Ag NPs, which are responsible for decreasing the number of recombination centers. In contrast to UV–vis light, performance improvement under vis irradiation occurs with increasing Ag₂O and Ag⁰ contents in the TiO₂/Ag₂O/Ag NTs as a result of the utilization of larger amounts of incident photons. The optimized samples reached phenol degradation rates of 0.50 and 2.89 μmol dm^–3 min^–1 under visible and UV light, respectively, which means degradation activities 3.8- and 2-fold greater than that of the reference sample, respectively, remained after four photodegradation cycles under UV light

Dependence between Ionic Liquid Structure and Mechanism of Visible-Light-Induced Activity of TiO₂ Obtained by Ionic-Liquid-Assisted Solvothermal Synthesis

Because of the tremendous structural diversity of ionic liquids (ILs), simple transfer of observations performed for one IL used for IL-TiO₂ preparation on different samples is not possible. Therefore, four ionic liquids, all containing distinct nitrogen-bearing organic cations (pyridinium, pyrrolidinium, ammonium, imidazolium), were used for the first time for the preparation of IL-TiO₂ composites. The role of the individual IL cation in the synthesis of TiO₂ microspheres, as well as the effect of the IL structure on the mechanism of the visible-light (Vis)-induced photoactivity of IL-TiO₂ was presented and discussed in regard to structure, morphology, absorption properties, elemental composition, and reactive species involved in the photocatalytic reaction of phenol degradation. The successful modification of the TiO₂ with organic IL species including possible interactions between IL and TiO₂ surface, as well as the TiO₂ matrix (doping with N), were confirmed. The sample that exhibited the highest photoactivity under Vis irradiation (58%) was TiO₂ prepared in a presence of 1-butylpyridinium chloride with a IL:precursor molar ratio of 1:3. For this sample, the highest partial decomposition of cationic species of IL was observed resulting in interaction of N atoms with deeper sites of TiO₂ (Ti-N_<i>x</i>) as well as the highest surface defects in a form of Ti³⁺. The superoxide radical species O₂^• – were found to be main active species responsible for high efficiency of degradation under Vis irradiation