Daichi Oka

Lithium Ion Battery Peformance of Silicon Nanowires with Carbon Skin

Silicon (Si) nanomaterials have emerged as a leading candidate for next generation lithium-ion battery anodes. However, the low electrical conductivity of Si requires the use of conductive additives in the anode film. Here we report a solution-based synthesis of Si nanowires with a conductive carbon skin. Without any conductive additive, the Si nanowire electrodes exhibited capacities of over 2000 mA h g(-1) for 100 cycles when cycled at C/10 and over 1200 mA h g(-1) when cycled more rapidly at 1C against Li metal. In situ transmission electron microscopy (TEM) observation reveals that the carbon skin performs dual roles: it speeds lithiation of the Si nanowires significantly, while also constraining the final volume expansion. The present work sheds light on ways to optimize lithium battery performance by smartly tailoring the nanostructure of composition of materials based on silicon and carbon.

Possible ferroelectricity in perovskite oxynitride SrTaO2N epitaxial thin films

Compressively strained SrTaO2N thin films were epitaxially grown on SrTiO3 substrates using nitrogen plasma-assisted pulsed laser deposition. Piezoresponse force microscopy measurements revealed small domains (101–102 nm) that exhibited classical ferroelectricity, a behaviour not previously observed in perovskite oxynitrides. The surrounding matrix region exhibited relaxor ferroelectric-like behaviour, with remanent polarisation invoked by domain poling. First-principles calculations suggested that the small domains and the surrounding matrix had trans-type and a cis-type anion arrangements, respectively. These experiments demonstrate the promise of tailoring the functionality of perovskite oxynitrides by modifying the anion arrangements by using epitaxial strain.

Intrinsic high electrical conductivity of stoichiometricSrNbO3epitaxial thin films

SrVO3 and SrNbO3 are perovskite-type transition-metal oxides with the same d1 electronic configuration. Although SrNbO3 (4d1) has a larger d orbital than SrVO3 (3d1), the reported electrical resistivity of SrNbO3 is much higher than that of SrVO3, probably owing to nonstoichiometry. In this paper, we grew epitaxial, high-conductivity stoichiometric SrNbO3 using pulsed laser deposition. The growth temperature strongly affected the Sr/Nb ratio and the oxygen content of the films, and we obtained stoichiometric SrNbO3 at a very narrow temperature window around 630

Stress stabilization of a new ferroelectric phase incorporated into SrTaO2N thin films

°

Composition-induced structural, electrical, and magnetic phase transitions in AX-type mixed-valence cobalt oxynitride epitaxial thin films

C. The stoichiometric SrNbO3 epitaxial thin films grew coherently on KTaO3 (001) substrates with high crystallinity. The room-temperature resistivity of the stoichiometric film was

Strain Engineering for Anion Arrangement in Perovskite Oxynitrides

2.82 {\times} 10^{-5} {\Omega}

Low temperature epitaxial growth of anatase TaON using anatase TiO2 seed layer

cm, one order of magnitude lower than the lowest reported value of SrNbO3 and comparable with that of SrVO3. We observed a T-square dependence of resistivity below

High-Mobility Electron Conduction in Oxynitride: Anatase TaON

T^{\ast}

Heteroepitaxial Growth of Perovskite CaTaO2N Thin Films by Nitrogen Plasma-Assisted Pulsed Laser Deposition

= 180 K and non-Drude behavior in near-infrared absorption spectroscopy, attributable to the Fermi-liquid nature caused by electron correlation. Analysis of the T-square coefficient A of resistivity experimentally revealed that the 4d orbital of Nb that is larger than the 3d ones certainly contributes to the high electrical conduction of SrNbO3.

Epitaxial growth and dimensionality-controlled MIT of Ruddlesden-Popper type Sr n +1 V n O 3 n +1 (001) thin films ( n = 1, 2)

Microstructural analyses of highly stressed SrTaO2N thin films deposited on SrTiO3 substrates by cathodoluminescence spectroscopy revealed coexistence of ferroelectric and relaxor-ferroelectric-like phases in the films. These two phases are, respectively, associated with “trans-type” and “cis-type” anion orders, as supported by the relative difference of the band gap energies calculated by first principles calculations based on the density functional theory. The formation of the new ferroelectric phase is considered to occur upon stabilization by the high compressive residual stress stored into the film structure, with the length/size of the “trans-type” region strongly depending upon the local stress state in the film.