Nb12O29 is a 4d transition metal oxide that occurs in two forms with different symmetries, monoclinic (m) and orthorhombic (o). The monoclinic form has unusual magnetic properties; below a temperature of 12 K, it exhibits both metallic conductivity and antiferromagnetic ordering. Here, first-principles densityfunctional theory calculations are used to study the structure, relative stability and electronic properties of Nb12O29. The optimized crystal structures are in good agreement with experimental observations and total energy calculations show similar stability of the two phases, while a magnetic electronic state is slightly favoured for m-Nb12O29. The unusual magnetism of the monoclinic phase originates from a Stoner instability that can be attributed to the Nb atoms with valence states close to Nb5+, i.e., the atoms with an electronic configuration of similar to d(0). This is in clear contradiction to current models in which the magnetism is attributed to the presence of localized Nb4+ ions with a formal d(1) configuration. Our study demonstrates that in complex structures, magnetic properties are best not inferred from ionic models, but require a full quantum mechanical calculation over the whole unit cell.@en

Cu(5)SbO(6) is found to have a monoclinic, Delafossite-derived structure consisting of alternating layers of O-Cu(I)-O sticks and magnetic layers of Jahn Teller distorted Cu(II)O(6) octahedra in an edge sharing honeycomb arrangement with Sb(V)O(6) octahedra. This yields the structural formula Cu(I)(3)Cu(II)(2)Sb(V)O(6). Variants with ordered and disordered layer stacking are observed, depending on the synthesis conditions. The spin 1/2 Cu(2+) ions form dimers in the honeycomb layer. The magnetic susceptibility measured between 5 and 300 K is characteristic of the presence of a singlet-triplet spin gap of 189 K. High resolution synchrotron X-ray diffraction studies indicate that changes in the intra- or interdirner distances between 300 and 20 K, such as might indicate an increase in strength of the Peierls-like distortion through the spin gap temperature, if present, are very small. A comparison to the NaFeO(2)-type Cu(2+) honeycomb compounds Na(3)Cu(2)SbO(6) and Na(2)Cu(2)TeO(6) is presented.@en

We report on the destabilization of the 6H-SrIrO3 polymorph through partial substitutions of zinc and lithium for iridium to form perovskites. The perovskites crystallize in the orthorhombic space group Pbnm: SrIr1-xZnxO3 is found for 0.25@en

The Yb-Ru-Sn ternary system was investigated and a new material, Yb(0.24)Sn(0.76)Ru, with a simple cubic crystal structure, was discovered. Yb(0.24)Sn(0.76)Ru has a smaller lattice parameter a = 3.217(4) angstrom, than its isostructural YbRu analogue (a = 3.360 angstrom). Both X-ray diffraction and electron microscopy techniques were used to refine the crystal structure of Yb(0.24)Sn(0.76)Ru. It was found that a new compound forms in the CsCl structure, with Ru on the la site and a (Yb,Sn) mixture on site 1b. The XRD Rietveld analysis provides the occupation of Yb equal to 0.24, in agreement with the single crystal nano-electron diffraction refinement, which gives the occupation 0.21@en

We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a ¿7-doublet ground state and a ¿8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a ¿6-excited state resides at 32 meV; however, the ¿8/¿6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the ¿7-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound@en

Bi2Se3 is one of a handful of known topological insulators. Here we show that copper intercalation in the van der Waals gaps between the Bi2Se3 layers, yielding an electron concentration of similar to 2 x 10(20) cm(-3), results in superconductivity at 3.8 K in CuxBi2Se3 for 0.12@en

The structural misfit compound (PbSe)(1.16) (TiSe2)(2) is reported. It is a superconductor with a T-c of 2.3 K. (PbSe)(1.16) (TiSe2)(2) derives from a parent compound, TiSe2, which shows a charge-density wave transition and no superconductivity. The crystal structure, characterized by high-resolution electron microscopy and powder x-ray diffraction, consists of two layers of 1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements suggest that the superconductivity is induced by charge transfer from the PbSe layers to the TiSe2 layers.@en