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Abstract: Polycrystalline perovskite cobalt oxides Sr1– xRx CoO3 (R=Y and Ho; ) were prepared by high-pressure/high-temperature technique. X-ray powder patterns of the Y-system indicated cubic perovskite form for , and orthorhombic perovskite form for and 1.0, while coexisting of the two phases for . The cubic perovskite samples had metallic electric resistivities while the orthorhombic ones with semiconducting or insulating nature. The parent compound SrCoO3 showed a ferromagnetic transition at 266K. With the Y substitution, the transition temperature increased slightly to ∼275K at , then decreased rapidly to ∼60K for . The YCoO3 () sample showed non-magnetic behavior. The Ho-substituted system showed quite similar structural, transport and magnetic properties to those of the Y-system. [Copyright &y& Elsevier]

New phases Sr8ARe3Cu4O24 (A=Sr,Ca) were discovered under high-pressure/high-temperature condition. X-ray powder diffraction and electron diffraction studies for these phases indicated that they have an ordered perovskite-type structure with cubic lattices of ∼8 A˚. They showed ferromagnetism at room temperature when they were synthesized under high-oxygen-pressure condition. The Ca-containing phase has a very high Tc of 440 K with a spontaneous magnetization of ∼1 μB/f.u. [Copyright &y& Elsevier]

Abstract: Polycrystalline perovskite cobalt oxides (Sr1– x Ca x )CoO3 (0⩽x⩽0.8) were synthesized under high pressure (6GPa) and high temperature (1200–1300 °C) conditions. Powder X-ray diffraction data confirmed that they have cubic perovskite structures. The end member of the solid solution, SrCoO3, exhibited a ferromagnetic transition with Curie temperature of and metallic electric conductivity. With increasing the Ca content , increased slightly to 286K at then decreased rapidly to 148K for . The origin of the ferromagnetism is discussed in relation to the spin state of the Co4+ ions. The present system showed a relatively large (∼5.5%) negative magnetoresistance for or 0.2 in the vicinity of T c. [Copyright &y& Elsevier]

Crystal structures of a homologous series of Co-based layered cuprates, CoSr2(Y,Ce)sCu2O5+2s (s=1–3), have been investigated by high-resolution electron microscopy (HREM) and electron diffraction (ED) techniques. For all the three phases ED patterns showed double periodicity along a direction parallel to the CoO layers, indicating a regular alternation of two types of CoO4-tetrahedra chains within the layers. Also seen was ordering of the chains along the layer-stacking direction for the s=1 phase (Co-1212); ED patterns simulated based on the proposed superstructure model well reproduced the observed patterns. For the s=2 (Co-1222) and s=3 (Co-1232) phases in which an additional fluorite-type layer-block is inserted between two CuO2 planes, HREM and ED analysis revealed complete disorder of the CoO4 chains along the layer-stacking direction. This implies that the interlayer ordering is mainly controlled by the distance between the neighboring CoO layers. [Copyright &y& Elsevier]

The novel spin-chain cobalt oxide Sr5Pb3CoO12 [P6×2m, a=10.1093(2) A˚ and c=3.562 51(9) A˚ at 295 K] is reported. A polycrystalline sample of the compound was studied by neutron diffraction (at 6 and 295 K) and magnetic susceptibility measurements (5 to 390 K). The cobalt oxide was found to be analogous to the copper oxide Sr5Pb3CuO12, which is comprised of magnetic-linear chains at an interchain distance of 10 A˚. Although the cobalt oxide chains (μeff of 3.64 μB per Co) are substantially antiferromagnetic (θW=−38.8 K), neither low-dimensional magnetism nor long-range ordering has been found; a local-structure disorder in the chains might have an impact on the magnetism. This compound is highly electrically insulating. [ABSTRACT FROM AUTHOR]

Abstract: Na2OsO4 crystals were grown by a NaCl flux method under high pressure. It crystallizes in the Ca2IrO4-type structure without having additional elements or metal vacancies, which are usually accommodated. It appears that Na2OsO4 is a metal-stoichiometric Ca2IrO4-type compound never been synthesized to date. Na2OsO4 has the octahedral environment of Os6+O6 so that the electronic configuration is 5d 2, suggesting the magnetic S=1 ground state. However, magnetization, electrical resistivity, and specific heat measurements indicated that the non-magnetic S=0 state is much likely for Na2OsO4 than the S=1 state. Band structure calculations and the structure analysis found that the disagreement is probably due to the statically uniaxial compression of the OsO6 octahedra, resulting in splitting of the band. [Copyright &y& Elsevier]

Abstract: The Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method using KOs2O6 as a host. The composition was identified as Na1.4Os2O6·H2O by electron probe micro-analysis, thermogravimetric analysis, and structural analysis using synchrotron X-ray diffraction. Na1.4Os2O6·H2O crystallizes in a regular pyrochlore structure with some defects (space group: Fd-3m, a=10.16851(1)Å). Electrical resistivity, heat capacity, and magnetization measurements clearly showed absence of superconductivity down to 2K, being in large contrast to what was found for the β-type pyrochlore superconductor AOs2O6 (A=Cs, Rb, and K). The Sommerfeld coefficient is 22mJK−2 mol−1, being the smallest among AOs2O6. A magnetic anomaly at ∼57K and associated magneto-resistance (+3.7% at 2K in 70kOe) were found. [Copyright &y& Elsevier]

Abstract: We prepared samples of cubic γ-MoN x (x∼0.5) by high-pressure–high-temperature synthesis. N atom site occupancies within the defect rock salt structure were determined from time-of-flight neutron diffraction and powder X-ray diffraction data by Rietveld analysis. The results show that N atoms occupy only octahedral sites within the structure. The semi-metallic compound is a superconductor, with determined by SQUID magnetometry. The compressibility of the material was determined by synchrotron X-ray diffraction measurements at high pressure in the diamond anvil cell. The vibrational density of states was studied by Raman scattering spectroscopy. [Copyright &y& Elsevier]

A new hexagonal perovskite-type oxide Ba8Ta4Ru8/3Co2/3O24 was synthesized by the solid-state method at 1573 K and characterized by electron diffraction (ED), time-of-flight (TOF) neutron powder diffraction, and magnetic susceptibility. Structure parameters of Ba8Ta4Ru8/3Co2/3O24 were refined by the Rietveld method from the TOF neutron powder diffraction data on the basis of space group P63/mcm and lattice parameters a=10.0075(1) Å and c=18.9248(2) Å as obtained from the ED data (Z=3). The crystal structure of Ba8Ta4Ru8/3Co2/3O24 consists of 8-layered (cchc)2 close-packed stacking of BaO3 layers along the c-axis. Corner-shared octahedra are filled by Ta only and face-shared octahedra are statistically occupied by Ru, Co, and vacancies. Similar compounds Ba8Ta4Ru8/3M2/3O24 with M=Ni and Zn were also prepared. Magnetic susceptibility measurements showed no magnetic ordering down to 5 K. [Copyright &y& Elsevier]

Non-resonant V L2,3 and OKα X-ray emission spectra of a new series of (Cu,V)Sr2Can−1CunOy (n=3–7) superconductors are presented. We have found that oxygen atoms surround V-atoms in the given compounds, form a (VO4)3− tetrahedrons and have a pentavalent state. This induces holes due to the substitution of divalent copper by pentavalent vanadium ions providing a hole-doping mechanism of superconductivity in this series of compounds. A spectral estimation of the oxygen concentration shows that the oxygen content under high-pressure/high-temperature synthesis conditions is not changed considerably from the start to the final product. [Copyright &y& Elsevier]

New phase (Nd,Ce)2+xCaCu2O6+y was prepared at a high-pressure/high-temperature condition of 6 GPa and 1300°C. It had a nonstoichiometric composition close to Nd2.16Ce0.225CaCu2O6+y. According to X-ray diffraction pattern, the Nd2.16Ce0.225CaCu2O6+y phase has a tetragonal lattice with a = 3.845(1) A˚, c = 19.349(5) A˚. However, electron microscopic observations revealed a complicated shear structure for this phase. Magnetic susceptibility and magnetic hysteresis measurements were performed for the Nd2.16Ce0.225CaCu2O6+y sample and it was found that the phase undergoes a weak ferromagnetic transition at 150 K. Below ≈40 K, complicated magnetic behavior was observed suggesting the presence of second weak ferromagnetic transition near 40 K. [Copyright &y& Elsevier]