Search

Polycrystalline layered Y2C with quasi-2D anionic electrons confined in the interlayer is prepared by melting stoichiometric amounts of Y shots and C granules under Ar.

LnCrAsO (Ln: La, Ce, Pr, Nd) is prepared by solid state reaction of stoichiometric mixtures of LnAs, Cr, and Cr2O3 (evacuated silica tube, 1273 K, 20 h).

FeAs-based layered superconductors such as F-doped LaFeAsO have recently been investigated intensively because of their high superconducting transition temperatures. Epitaxial films of these compounds are important to examine their intrinsic materials properties as well as to transfer them to device applications. In this review, we first present our research route from transparent p-type oxides semiconductors to the Fe-based superconductors. Then we review growth of epitaxial thin films for the layered oxychalcogenides and oxypnictides. Reactive solid-phase epitaxy technique was inevitable to prepare epitaxial thin films of the oxychalcogenides and Zn-based oxypnictides. On the other hand, epitaxial thin films of Mn-based oxypnictides were grown by standard pulsed laser deposition. These techniques, however, did not grow epitaxial thin films for LaFeAsO. Thus, we developed a modified pulsed laser deposition process and succeeded in obtaining epitaxial thin films of FeAs-based superconductors, LaFeAsO and cobalt-doped SrFe 2 As 2 .

A new synthetic route via a solid-state reaction, the crystal structure of 12SrO·7Al2O3 (S12A7) incorporated with OH− ions, and the formation of oxygen radical anions in S12A7 have been examined. Investigations using X-ray powder diffraction and thermogravimetric and evolved gas combined analyses demonstrate that homogenization promoted by molten Sr(OH)2 hydrates and the presence of Sr-hydrogarnet precursors play crucial roles in the formation of S12A7. Rietveld analyses confirm the lattice framework of S12A7 has a structure identical to that of the nanoporous crystal 12CaO·7Al2O3 (C12A7, a mayenite structure) and demonstrate that two Sr2+ ions (pole Sr2+ ions) on the S4 axis of a cage displace toward the cage center owing to the accommodation of an OH− ion. An electron paramagnetic resonance study demonstrates that oxygen radical anions, O2− and O−, are generated in the cages with concentrations on the order of 1020 cm−3 each by oxygen annealing. From the g-values observed at 77 K, the oxygen radical ani...

Rietveld analysis of the powder X-ray diffraction of a new layered oxyarsenide, LaNiOAs, which was synthesized by solid-state reactions, revealed that LaNiOAs belongs to the tetragonal ZrCuSiAs-type structure (P4/nmm) and is composed of alternating stacks of La-O and Ni-As layers. The electrical and magnetic measurements demonstrated that LaNiOAs exhibits a superconducting transition at 2.4 K, and above this, LaNiOAs shows metallic conduction and Pauli paramagnetism. The diamagnetic susceptibility measured at 1.8 K corresponded to {approx}20% of perfect diamagnetic susceptibility, substantiating that LaNiOAs is a bulk superconductor. - Graphical abstract: A new layered oxyarsenide, LaNiOAs, which exhibits a superconducting transition at 2.4 K, was synthesized by solid-state reactions. This compound had a tetragonal ZrCuSiAs-type structure similar to recently discovered superconductors, LaFeOP, LaFeOAs, and LaNiOP. Superconductivity was observed for undoped LaNiOAs, which differs from the case of LaFeOAs. Display Omitted.

Crystal structures, optoelectronic properties, and electronic structures of layered oxychalcogenides BiCuOCh (Ch = S, Se, Te) have been compared to those of LaCuOCh, with an emphasis on the electronic configurations of Bi3+ (5d106s2) and La3+ (5d06s0). The BiCuOCh series were expected to exhibit better hole-transport properties than the LaCuOCh series because the pseudo-closed-shell 6s2 electronic configuration of the Bi3+ cation was expected to form valence band maxima (VBM) by admixing with the p orbitals of the Ch anions. However, the two series of compounds exhibited similar electrical properties, suggesting that the contribution of the Bi 6s orbitals to the VBM is small in BiCuOCh. The crystal structures and optical properties showed distinct differences; for example, the band gaps of BiCuOCh were smaller than those of LaCuOCh. These findings can be understood on the basis of the electronic structures obtained by photoelectron spectroscopy and density functional theory calculations. The Bi 6s orbital...

A layered oxyphosphide, LaNiOP, was synthesized by solid-state reactions. This crystal was confirmed to have a layered structure composed of an alternating stack of (La(3+)O(2-))(+) and (Ni(2+)P(3-))(-). We found that the resulting LaNiOP shows a superconducting transition at approximately 3 K. This material exhibited metallic conduction and Pauli paramagnetism in the temperature range of 4-300 K. The resistivity sharply dropped to zero and the magnetic susceptibility became negative at4 K, indicating that a superconducting transition occurs. The volume fraction of the superconducting phase estimated from the diamagnetic susceptibility reached approximately 40 vol % at 1.8 K, substantiating that LaNiOP is a bulk superconductor.

We report superconductivity in an iron-based layered oxy-pnictide LaOFeP. LaOFeP is composed of an alternate stack of lanthanum oxide (La3+O2-) and iron pnictide (Fe2+P3-) layers. Magnetic and electrical resistivity measurements verify the occurrence of the superconducting transition at approximately 4 K.

The optical and electronic properties of a wide-gap (∼3.3 eV) layered oxychalcogenide, La2CdO2Se2, were examined using epitaxial thin films prepared by a reactive solid-phase epitaxy. Two optical absorption peaks due to exciton split by the spin−orbit interaction were observed at 3.43 and 3.61 eV at 10 K near the absorption edge. A sharp ultraviolet photoluminescence was observed even at room temperature, indicating that the free exciton had a large binding energy (estimated value = ∼40 meV) similar to Cu-based, layered oxychalcogenides LnCuOCh (Ln = lanthanide, Ch = chalcogen). The optical properties were compared to those of the Cu-based oxychalcogenides and low-dimensional CdSe-based materials. It is concluded that the two-dimensional crystal structure, which remarkably reduces the bandwidth of the conduction band, is a major origin for the wide band gap. Energy band calculations indicate that the holes are confined in the two-dimensional (CdSe2)2- layer, which is most likely responsible for the large ...

A series of layered oxysulfides, LnCuOS (Ln = La∼Nd), was studied to examine the influence of these lanthanide ions on their optical and electrical transport properties. PrCuOS and NdCuOS showed wide-gap p-type semiconducting properties similar to LaCuOS, which is a p-type semiconductor with an energy gap of 3.1 eV. A sharp photoluminescence peak near the absorption edge, which originates from excitons, was observed in LnCuOS (Ln = La, Pr, and Nd), indicating that these lanthanide ions do not influence the fundamental optical properties and excitons are confined in (Cu2S2)2- sulfide layers sandwiched between (Ln2O2)2+ oxide layers. On the other hand, CeCuOS showed p-type degenerate semiconducting behavior and its color was black. The electronic structures of LnCuOS (Ln = La∼Nd) were investigated by ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy to understand these differences derived from the lanthanide ions. Although no remarkable difference in the electronic structures was...