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The electronic structure, magnetism and Fermi surface of a hole self-doped potential iron-based superconductor KCa 2 Fe 4 As 4 O 2 (12442) were studied by a first-principles DFT/GGA approach. The self-doping value is obtained from DFT is 0.75 hole on Fe-3d states for KCa 2 Fe 4 As 4 O 2. Surprisingly, for the KCa 2 Fe 4 As 4 O 2 it was found that except the Fe-3d bands the O-2p bands also cross the Fermi level, which is quite anomalous behavior for O-2p states. In general, the O-2p states are usually fully occupied in transition metal oxides. Here it is not the case due to the fact that CaO layer gives some of the electrons to the FeAs layer, thus leaving O-2p states partially occupied. The O-2p states form additional Fermi surface sheet with propeller-like shape around Γ -point and modify the Fe-3d Fermi surface sheets due to the hybridization. To prove the presence of anomalous metallic O-2p band in KCa 2 Fe 4 As 4 O 2 the comparative study with the same family systems KCa 2 Fe 4 As 4 F 2 and RbGd 2 Fe 4 As 4 O 2 (where it is not the case) was performed. Finally, we discuss the main differences between the emergence of the metallic O-2p band in case of KCa 2 Fe 4 As 4 O 2 and those in case of cuprate superconductors LaBaCuO 4 and YBa 2 Cu 3 O 7. Therefore, we expect that the KCa 2 Fe 4 As 4 O 2 might be a potential superconductor with unusual properties. [ABSTRACT FROM AUTHOR]

The hydrodynamics of plasma formed in the interaction of 100 ns UV KrF laser pulses with foam targets with volume densities from 5 to 500 mg/cm3 was studied. Initial and dynamic transmittance at 248 nm wavelength were measured. At intensities of about 1012 W/cm2, the propagation rates of radiation through foam targets reached 80 km/s, while plasma stream velocities from both the front and rear sides of targets were approximately the same, ~ 75 km/s, which confirms a volumetric absorption of radiation within the target thickness and the explosive nature of the plasma formation and expansion. [ABSTRACT FROM AUTHOR]

The paper presents an original approach to the synthesis of polycalciumorganyl silsesquioxanes through the reaction of polyorganyl silsesquioxanes [RSiO1.5]n (where R is an ethyl and phenyl radical) with sea urchin skeleton under the conditions of mechanochemical activation. The novelty and practical significance of the present study lies in the use of an available natural raw source as a source of calcium ions to initiate the reaction of calcium silicate formation and create a matrix for the formation of a porous inorganic composite framework. The thermal stability of the introduced silicates, i.e., the ability to maintain a porous structure at high temperatures, is key to the production of an ordered porous material. The reaction scheme was proposed to be based on the interaction of calcium carbonate with the siloxane bond. FTIR, XRD, GPC, and TGA were used to study the composition and structure of the obtained materials. The cross-sectional area of the polymer chain and the volumes of the coherent scattering regions of the polymers obtained were calculated from the XRD data. To prepare the composites, the sea urchin skeleton was further modified with polycalciumorganyl silsesquioxanes in a toluene solution. To remove the sea urchin skeleton, the obtained biomimetic composites were treated with hydrochloric acid. The results of the morphological and surface composition studies are reported. The method proposed in the paper could be of fundamental importance for the possibility of obtaining structured porous composite materials for a wide range of practical applications, including for the purpose of creating a composite that may be a promising carrier for targeted delivery of chemotherapy agents. [ABSTRACT FROM AUTHOR]

We successfully synthesized bulk Ba0.6Na0.4Fe2As2 and Sr0.5Na0.5Fe2As2 compounds by high-energy mechanical alloying (MA) technique. The MA process results in homogeneous amorphous phases of BaFe2As2 and SrFe2As2. It was found that the optimum time for high-energy milling in all cases is about 1.5–2 h, and the maximum amount of amorphous phase could be obtained when energy of 50–100 MJ/kg was absorbed by the powder. After a short-term heat treatment, we obtained nearly optimum sodium-doped Ba1−xNaxFe2As2 and Sr1−xNaxFe2As2 superconducting bulk samples. Therefore, MA is a potential scalable method to produce bulk superconducting material for industrial needs. [ABSTRACT FROM AUTHOR]

In the stoichiometric iron-based superconductor EuRbFe4As4, superconductivity coexists with a long-range magnetic ordering in Eu layers. Using high-resolution transmission electron microscopy (HRTEM), we observed an atomic structure of as-grown EuRbFe4As4 crystals. HRTEM shows that crystals have two-dimensional intrinsic nanoinclusions established to be the RbFe2As2 (122) phase with a volume fraction of ~5.6%. In contrast with the CaKFe4As4 compound, similar inclusions are not superconducting down to 2 K, and no second magnetization peak was observed in the magnetization measurements at low temperature with B ‖ ab. We show that the non-superconducting 122 phase nanoinclusions could act as 2D pinning centers. [ABSTRACT FROM AUTHOR]

[Display omitted] Here we report the high-pressure synthesis of a series of lanthanum–yttrium ternary hydrides obtained at pressures of 170–196 GPa via the laser heating of P 6 3 /mmc La–Y alloys with ammonia borane. As a result, we discovered several novel compounds: cubic hexahydride (La,Y)H 6 and decahydrides (La,Y)H 10 with a maximum critical temperature T C ∼ 253 K and an extrapolated upper critical magnetic field B C2 (0) of up to 135 T at 183 GPa. The current–voltage measurements show that the critical current density J C in (La,Y)H 10 is 12–27.7 kA/mm2 at 4.2 K, which is comparable with that of commercial superconducting wires such as NbTi and Nb 3 Sn. (La,Y)H 6 and (La,Y)H 10 are among the first examples of ternary high- T C superconducting hydrides. Our experiments show that part of metal atoms in the structures of recently discovered Im 3 ¯ m -YH 6 and Fm 3 ¯ m -LaH 10 can be replaced with lanthanum (∼70%) and yttrium (∼25%), respectively, with the formation of unique ternary superhydrides containing metal-encapsulated cages La@H 24 and Y@H 32 , which are specific for Im 3 ¯ m -LaH 6 and Fm 3 ¯ m -YH 10. This work demonstrates that hydrides, unstable in pure form such as LaH 6 and YH 10 , may nevertheless be stabilized at relatively low pressures in solid solutions with superhydrides having the desired structure. [ABSTRACT FROM AUTHOR]