Masaya Uchida

Modulated Structure of Misfit-Layered Cobalt Oxide [Ca2(Co0.65Cu0.35)2O4]0.63CoO2

We have determined the crystal structure of novel thermoelectric compound [Ca2(Co0.65Cu0.35)2O4]0.63CoO2 by a superspace group approach. Structural parameters have been refined with a superspace group of C2/m(1 p 0)s0 using powder neutron diffraction data collected at 293 K. The compound consists of mutually interpenetrating triangular CoO2 layers and distorted four-layered rock salt-type Ca2(Co0.65Cu0.35)2O4 slabs, which are incommensurate parallel to the b-axis. The CoO2 layer is composed of the CdI2-type edge-shared CoO6 octahedra. Both the subsystems have common a- and c-axes, and β-angle with a=4.8212(4) A, c=12.7671(8) A and β=93.93(1)°. The b-axis lengths are b1=2.8103(3) A for the [CoO2] subsystem and b2=4.4915(3) A for the [Ca2(Co0.65Cu0.35)2O4] subsystem. A marked displacive modulation of the (Co,Cu) and O sites in the [Ca2(Co0.65Cu0.35)2O4] subsystem has been observed, yielding a large fluctuation of the (Co,Cu)–O distances in the range from 1.8 A to 2.7 A. Cu2+ ions appear to play an important role in stabilizing such a four-atom thick subsystem in this compound.

Nanoparticles of amorphous ruthenium sulfide easily obtainable from a TiO2-supported hexanuclear cluster complex [Ru6C(CO)16]2-: a highly active catalyst for the reduction of SO2 with H2.

TiO(2)-supported ruthenium-metal particles were derived from an anionic hexanuclear carbido carbonyl cluster [Ru(6)C(CO)(16)](2-) and compared with those prepared conventionally by impregnation of TiO(2) with a solution of RuCl(3) followed by reduction with H(2). The average sizes of the metal particles in both systems are similar, that is, 12 A for molecular cluster-derived particles and 15 A for those derived from the RuCl(3) precursor, although the size distribution is sharper in the former case. These supported particles efficiently promote the reduction of SO(2) with H(2) to give elemental sulfur. Their active form is ruthenium sulfide as confirmed by EXAFS and X-ray diffraction measurements. The nanoscale ruthenium sulfide particles, which originated from the cluster complex, have an amorphous character and show activity even at low temperature (463 K), whereas ruthenium sulfide formed from RuCl(3)-derived metal dispersion is a pyrite-type RuS(2) crystallite and needs a temperature above 513 K to effect the same catalysis. Amorphous ruthenium sulfide maintains its nano-sized scale (approximately 14 A) regardless of the reaction temperature, while RuS(2) crystallite aggregates to form larger nonuniform particles.

The pseudocubic approximant Mg51Zn20 interpreted as a modulated crystal

Abstract The structure of the pseudocubic Mg51Zn20 phase, which is related to icosahedral quasicrystals, was interpreted as a modulated crystal. It basically comprises distorted close-packed layers with ordered atomic vacancies. The basic reciprocal-lattice vectors point to the vertices of a distorted icosahedron. A relationship in reciprocal space between the Mg51Zn20 phase and the icosahedral Zn-Mg-Dy quasicrystal was also investigated.

Role of dislocations on the formation of the Abrikosov lattice in Nb superconductor

Abstract Quantized magnetic flux lines (vortices) in superconducting Nb foils were directly observed with various externally applied magnetic fields in a cryo-Lorentz electron microscope. The interaction between vortices and dislocations was examined; edge-on dislocations weakly pin individual vortices at magnetic fields below 100xa0G. In higher magnetic fields the formation of a regular hexagonal vortex lattice starts preferentially at in-plane dislocations. At 200xa0G small domains of the Abrikosov vortex lattice is formed. Based on these observations the mechanism for the formation of the Abrikosov lattice is proposed.

Hexagonal Frank-Kasper phases interpreted as modulated crystals

The structures of the hexagonal Frank--Kasper phases F and K, which have been described in terms of the aggregation of clusters, are interpreted as modulated crystal structures. They are basically composed of two close-packed layers with ordered atomic vacancies rotated by 90 degrees to each other about their normal.