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The cohesive energy of W and Mo nanoparticles is modeled by considering W and Mo nanoparticles as Wulff construction. The energetic characteristics of Wulff construction is described by accounting for bond number in a system. The model predictions are consistent with the corresponding experimental results, especially when the diameter of nanoparticle is smaller than 1nm, which implies the closed packed structure for small nanoparticles.

In this study, we report comparative luminescence properties of multi-layer InGaN quantum dots grown on C- and R-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). High-density InGaN quantum dots (QDs) are formed on GaN templates by decreasing the growth temperature and increasing the adatom hopping-barrier through surface passivation. Atomic force microscopy (AFM) has been employed to estimate the size and height of these dots. Photoluminescence (PL) spectra recorded from (1120) InGaN QDs/(1102) sapphire show much stronger emission intensity compared to spectra recorded from (0001) InGaN QDs/(0001) sapphire. Due to the absence of strong spontaneous polarization and piezoelectric field, such (1150) InGaN QDs in the active layers would lead to high efficiency light emitting devices. (c) 2005 Elsevier B.V. All rights reserved.

A new compound with a cubic structure, (Ba{sub 0.05}K{sub 0.95})BiO{sub 3}{center_dot}1/6H{sub 2}O (BKBO), was synthesized by electrochemical crystal growth using a rotating anode in molten KOH flux at 255 C. The BKBO crystal had the KSbO{sub 3} structure and belonged to space group Im{bar 3} (No 204) with Z = 12. Refinement of X-ray diffraction data at room temperature gave a = 10.0204(2) {angstrom}, V = 1006.1(1) {angstrom}{sup 3}, and R = 2.4% for 1465 unique reflections. Potassium, barium, and hydrated oxygen were found to occupy different sites in the tunnel structure. The electrical conductivity at room temperature was similar to the ionic conductor KBiO{sub 3}. BKBO decomposed to Bi{sub 2}O{sub 3}, K{sub 2}O, and BaO above 400 C.

A method is described for the growth of large single crystals of cubic BKBO. The improved technique uses top-seeded growth from Na-free compositions through use of a BKBO reference electrode. By careful control of over-potential it is possible to control the K content (ϰ) and homogeneity in the crystals. For ϰ = 0.38 the highest T c was obtained (32 K) with a sharp transition ( ΔT = 1 K). Details are reported for the crystal growth process and the superconducting properties.

We report DC magnetization measurements of high quality single crystals of superconducting Ba_(0.63)K_(0.37)BiO_3 with T_c = 29 K, yielding values for the upper and lower critical fields, the low field critical current, the magnetization relaxation rate, and the activation energy for flux motion. We contrast the magnetization relaxation results for isotropic Ba_(0.63)K_(0.37)BiO_3 with those obtained on highly anisotropic oxygen deficient single crystals of YBa_2Cu_3O_(7-δ) with δ = 0.58 and a comparable T_c= 35 K.

A systematic investigation was carried out on the effect of flux composition on the growth of crystals in the Bi-Ca-Sr-Cu-O system. 2021 superconducting single crystals were grown in oxygen from a Cu-rich flux in silver crucibles. Phase pure 2122 single crystals were obtained from stoichiometric melts in alumina crucible. Larger 2122 crystals could be obtained from fluxes with small amounts of Cu and Ca in excess. 2223 crystals could not be grown by flux methods (but by crystallization of rapidly solidified material). The effects of fluxing agents and starting composition on intergrowth content, crystals morphology and superconducting properties are discussed.

Hiroi et al. have recently reported the occurrence of superconductivity at a transition temperature of ~ 70 K in Sr2CuO3+δ. They observed a superstructure with lattice constants of Neutron diffraction studies on this compound by Shimakawa et al. indicate that the apical oxygen is fully occupied, whereas the oxygen in CuO2 plane is half occupied. If oxygen does not fully occupy in the conducting CuO2 planes, it raises doubts about our current understanding of superconductivity in the cuprates, which relies on full oxygen occupancy for the CuO2 planes.Recently, Han et al. observed a dependence of Tc on post annealing treatment of the high pressure synthesized Sr2CuO3+δ. They noticed that heating the sample to 300°C increased the Tc from 70 K to 94 K and that further heating to 450°C caused the sample to lose superconductivity.In order to investigate the structural and microchemical details of Sr2CuO3+δ, transmission electron diffraction, high resolution electron microscopy, and electron energy loss spectroscopy are employed.