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A semiconductive oxide, La2CuO4 (LCO), was investigated as a potential material to compose photocathode for sunlight-driven hydrogen evolution by splitting water. LCO, despite involving partially filled Cu 3d orbitals, behaves as a semiconductor and absorbs visible light on the bandgap formed by significant Coulomb repulsion between the electronic orbitals. An epitaxial LCO film was grown on a SrRuO3/SrTiO3 (SRO/STO) single-crystal substrate by pulsed laser deposition to obtain a photocathodic specimen for water photo-splitting. An LCO photocathode dressed with a Pt cocatalyst for hydrogen evolution (Pt/LCO/SRO/STO) exhibited a cathodic photocurrent with a density of 0.4 mA cm−2 at 0 VRHE under simulated AM1.5 G sunlight. This photocathode responded to incident light up to 800 nm, which is one of the longest wavelengths so far reported for an oxide photoelectrode. Together with a counter-electrode for oxygen evolution, the Pt/LCO/SRO/STO photocathode generated hydrogen with the expected H2 : O2 = 2 : 1 stoichiometric ratio with a Faradaic efficiency of approximately 80%. [ABSTRACT FROM AUTHOR]

A phase transformation induced by reduced particle size was investigated for NaNbO(sub 3) powders prepared through microemulsion-mediated synthesis and subsequent annealing treatment. The effect of particle structure on the phase transformation of the prepared NaNbO(sub 3) powders was studied using X-ray powder diffraction Raman spectroscopy, and nuclear site group based on these spectroscopic data and a possible mechanism of the phase transformation is suggested.

Abstract: Pure sodium potassium niobates with K0.5Na0.5NbO3 composition were prepared in powderous form with various particle sizes (75nm–10μm) through microemulsion mediated synthesis and subsequent annealing. An interesting change of particle shape and a mixture of fine and coarse particles were observed at a critical diameter of 200nm. A combined study by X-ray powder diffraction (XRPD) and Raman spectroscopy demonstrated a phase transformation induced by particle size. Fine particles (<200nm) have a triclinic structure whereas coarse particles (>200nm) have a monoclinic structure at room temperature. Possible space groups describing both these modifications were suggested. [Copyright &y& Elsevier]

Abstract: The present study reports on the synthesis of nanocrystalline (K x ,Na1− x )NbO3 powders prepared via microemulsion mediated hydrolytic decomposition of mixed alkoxide solutions. Compositions with different K/Na ratios ranging between the two end members KNbO3 and NaNbO3 have been synthesized and characterized with respect to stoichiometry, purity, crystalline structure, particle size and powder morphology using X-ray diffraction, Raman spectroscopy and inductively coupled plasma with optical emission spectroscopy. Both raw as well as calcined powders were investigated. For the technically relevant and piezoelectric most active composition (K0.50,Na0.50)NbO3 the results are presented and discussed in comparison to micron-sized and submicron-sized powders, that have been prepared by solid state reaction for reference. The study of the crystallographic structure of these reference powders by XRD and Raman spectroscopy confirms the size induced phase transition between the thermodynamically stable monoclinic modification for large particles towards a new triclinic polymorph, which has been reported for nano-powders of this composition by us previously. As possible origin for this phenomenon, internal OH− groups, variations in K-/Na-site occupancy and mechanical stresses arising from the large surface curvature of the nanocrystalline powders are addressed. [Copyright &y& Elsevier]

A particle size dependent modification in crystal structure of submicron KNaNb2O6 powders was observed for the first time by X-ray diffraction coupled with Raman spectroscopy. We saw a clear correlation between crystal size and crystallographic structure. Particles larger than 200 nm in diameter consisted of a perovskite type monoclinic phase whereas particles smaller than 200 nm were found to be triclinic. The lattice parameters were refined for both modifications and possible space groups defining the modifications were given. [Copyright &y& Elsevier]

Two different processes, which lead to formation of multishell fullerenes, are reported and discussed. The first process is 3000°C high temperature treatment of C 60 -containing carbon blacks. The second process is laser vaporization of composite carbon targets, containing C 60 and vapor-grown carbon fibers (VGCF). It has been shown that the laser vaporization technique allows increasing the yield up to 40%. Possible mechanisms of formation of the outer shells are discussed. [ABSTRACT FROM PUBLISHER]