Yasushi Kanke

Magnetic Properties of NaV6O11

Magnetic properties and electrical resistivity of NaV 6 O 11 single crystal have been investigated. Magnetic transition was observed at 64.2 K. This oxide having a hexagonal crystal structure exhibited a uniaxial magnetic anisotropy with the easy axis of magnetization parallel to [001]. The spontaneous magnetization at 5 K was 1.7µ B per formula unit. The resistivity perpendicular to [001] showed an anomaly at the Curie temperature similar to that of ferromagnetic metals, while that parallel to [001] showed no such anomaly. This behavior suggests the itinerant character of d electrons.

TiC–diamond composite disk-heater cell assembly to generate temperature of 2000 °C in a large-volume belt-type high-pressure apparatus at 10 GPa

A TiC–diamond composite was prepared for the heater of a large-volume belt type high-pressure apparatus. Graphite has conventionally been used for the heater in high-pressure studies, but it cannot be used at pressure higher than 10 GPa and above 1500 °C because of the problem associated with the graphite-to-diamond phase transformation. New TiC–diamond heater overcomes this problem and achieves stable temperature generation by using a belt-type high-pressure apparatus. The composite was fabricated by heat-treatment of a mixture of diamond and TiC0.8 with nonstoichiometric composition at ambient pressure. By optimizing the preparation conditions, we obtained TiC–diamond composites that exhibited mechanical and electrical properties suitable for a heater material without any volatile component such as resin. Since reported conventional TiC–diamond composite heaters include epoxy resin as binder, volatile components arise from decomposition of the resin at high temperature preventing stable high-pressure/hi...

Synthesis and structure refinement of SrTx>V6−xO11 (T =Ti, Cr, and Fe)

Abstract Four new phases, SrV 6 O 11 , SrTi x V 6− x O 11 (0 x V 6− x O 11 (0 x ≤ 1.0), and SrFe x V 6− x O 11 (0 P 6 3 / mmc ) and are isostructural with NaV 6 O 11 , BaTi 2 Fe 4 O 11 , and BaSn 2 Fe 4 O 11 . The structures of SrTiV 5 O 11 , SrTi 1.5 V 4.5 O 11 , SrCrV 5 O 11 , and SrFeV 5 O 11 were refined by Rietveld analysis of their neutron powder diffraction data. Some structural features of these four compounds are discussed in comparison with those of SrV 6 O 11 , BaTi 2 Fe 4 O 11 , and BaSn 2 Fe 4 O 11 .

Heater cell for materials synthesis and crystal growth in the large volume high pressure apparatus at 10 GPa

To realize materials synthesis and crystal growth in a large volume of high pressure apparatus in the region of 10 GPa, a heater cell was developed for a belt-type high pressure apparatus with a bore diameter of 32 mm. The cell consists of a cylindrical electrode made of TiC powders located between a pair of graphite heaters with a disk shape. High temperature of 1500 °C at nominal pressure of 9.7 GPa (9.35 GPa corrected) was successfully generated for 1 h using the cell. Synthesis and growth of stishovite was performed at high pressure and high temperature conditions based on their calibrations. Experimental results suggest that the materials synthesis and crystal growth above 10 GPa can be realized in a large volume of belt-type apparatus using the heater cell.

Fabrication and Characterization of Integrated Ultrahigh-Density Fe-Pt Alloy Nanowire Arrays on Glass

A method is reported for the fabrication of Fe-Pt binary alloy nanowire arrays embedded in porous alumina films with controlled diameters and high aspect ratios directly on glass substrates by successive anodization and cathodic electrodeposition in a novel bath with a simple composition. Porous alumina films with different pore sizes were initially formed by anodizing aluminum layers sputter-deposited on glass substrates covered with an indium tin oxide (ITO) film. After the insulative barrier layer was removed through a chemical dissolution, the porous alumina nanostructures on ITO/glass were used as template electrodes in dc electrodeposition to deposit Fe-Pt alloy within the nanopores, leading to integrated Fe-Pt nanowire (Φ23-52 nm) arrays on glass with high densities of 1.92-7.85 × 10 1 4 wire per square meter. The as-deposited Fe-Pt nanowires are composed of polycrystalline tetragonal FePt phase with crystal sizes 2-6 nm across. Thermal annealing at 973 K induced the crystal growth of disordered tetragonal FePt phase with appearance of (001) facet and developed the preferential magnetic orientation and enhanced coercivity in perpendicular direction (along the nanowire axis).

Phase equilibrium study of the system NaV2O5V2O3V2O5 at 923 K

Abstract The phase diagram of the system NaV 2 O 5 V 2 O 3 V 2 O 5 at 923 K was established. Two new phases, δ -Na x V 2 O 5 (0.55 ≤ x ≤ 0.57) and Na x V 12 O 29 (0.55 ≤ x ≤ 0.65), were found. The δ-Na x V 2 O 5 is hygroscopic and isostructural with δ-Ag x V 2 O 5 . The Na x V 12 O 29 is a member of a homologous series of compounds M x V 6 n O 15 n − m found also for M = Li or Cu. The dc conductivity of a single crystal of NaV 6 O 11 was measured at 5–298 K.

Structure of Ga2O3(ZnO)6: a member of the homologous series Ga2O3(ZnO)m

The structure of Ga(2)O(3)(ZnO)(6) was determined using single-crystal X-ray diffraction techniques in the space group Cmcm. The metal ion sublattice resembles some of the Zn ions in the wurtzite ZnO structure. The oxygen ion sublattice in Ga(2)O(3)(ZnO)(6) also resembles some of the O ions in ZnO. Structural relationships between Ga(2)O(3)(ZnO)(6) and ZnO are discussed, illustrating the process for obtaining the centrosymmetric Ga(2)O(3)(ZnO)(6) structure from the noncentrosymmetric ZnO. Structures of phases in the homologous series Ga(2)O(3)(ZnO)(m) are predicted on the basis of the structural data for Ga(2)O(3)(ZnO)(6). The structures of even m are constructed by simply extending the structure units seen in Ga(2)O(3)(ZnO)(6), while those of odd m consist of structure units which are of different types from those used for even m.

Crystal structure and magnetism of SrV6O11 single crystals

Magnetic property and specific heat of mixed valence vanadium oxide SrV6O11 were investigated. Single crystals and polycrystals were synthesized with a solid state reaction. Four-circle x-ray structural analysis discovered a structural transition at a temperature range between room temperature and 353 K. This transition corresponds to that of NaV6O11 at 245 K. Specific heat measurement of SrV6O11 was performed between 20 and 150 K and two anomalies were observed at 42 and 73 K. These anomalies are consistent with the two peaks in the temperature dependence of magnetization. Below 42 K, SrV6O11 shows metamagnetism and its critical field is about 4 T at 5 K. Its basic magnetic structure at 73 K is considered to be an antiferromagnetic state formed by the localized electron system.

Phase equilibrium study of the system CuV2O5V2O4V2O5

Abstract The phase diagram of the system CuV 2 O 5 V 2 O 4 V 2 O 5 at 923 K was established. Two new phases, Cu x V 9 O 22 (0.87 ≤ x ≤ 1.73) and Cu x V 12 O 29 (1.0 ≤ x ≤ 1.9), were found instead of the oxygen-deficient β′-Cu x V 2 O 5 reported earlier. Including β′-Cu x V 2 O 5 , they form a homologous series of bronze phases Cu x V 6 n O 15 n−m . These phases are closely related to β- and β′-Li x V 6 n O 15 n−m found previously. Factors bounding the maximum M content in M x V 6 n O 15 n − m ( M = Cu, Li) are discussed. The dc conductivities along the b -axis of the single crystals of the new phases were measured.

Synthesis and magnetic property of NaFe3V9O19

A new phase, NaFe3V9O19, was found. It crystallizes hexagonal with a = 5.8400 ± 0.0001 and c = 22.8058 ± 0.0005 A. Its possible space groups are P63mmc, P62c, or P63mc. The composition and the crystal data indicate that NaFe3V9O19 is isostructural with magnetoplumbite-type compounds. NaFe3V9O19 shows a uniaxial magnetism with the easy axis of magnetization parallel to [001] below the transition temperature, around 240 K.