https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/202086/1/j.scriptamat.2015.07.021.pdf

First principles phonon calculations in materials science

Phonon plays essential roles in dynamical behaviors and thermal properties, which are central topics in fundamental issues of materials science. The importance of first principles phonon calculations cannot be overly emphasized. Phonopy is an open source code for such calculations launched by the present authors, which has been world-widely used. Here we demonstrate phonon properties with fundamental equations and show examples how the phonon calculations are applied in materials science.

Magnetic fluid hyperthermia: focus on superparamagnetic iron oxide nanoparticles.

Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

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Hierarchically porous materials: synthesis strategies and structure design

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

A SPASER, short for surface plasmon amplification by stimulated emission of radiation, is key to accessing coherent optical fields at the nanoscale. Nevertheless, the realization of a SPASER in the visible range still remains a great challenge because of strong dissipative losses. Here, we demonstrate that room-temperature SPASER emission can be achieved by amplifying longitudinal surface plasmon modes supported in gold nanorods as plasmon nanocavities and utilizing laser dyes to supply optical gain for compensation of plasmon losses. By choosing a particular organic dye and adjusting the doping level, the resonant wavelength of the SPASER emission can be tuned from 562 to 627 nm with a spectral line width narrowed down to 5–11 nm. This work provides a versatile route toward SPASERs at extended wavelength regimes.

/pdf/wavelength-tunable-spasing-in-the-visible-4vfsyajqen.pdf

Wavelength-tunable spasing in the visible.

We report on observations of random lasers with coherent feedback in highly transparent polymer films embedded with silver nanoparticles. The hybrid materials were fabricated via in situ synthesis method, through which silver nanoparticles were precipitated by thermal treatment. Sharp peaks with linewidth ∼0.5nm were observed to emerge on the broad emission background when the pump energy reached a threshold, together with unidirectional laser irradiation. Random lasers with coherent feedback induced by silver nanoparticles have been rarely reported, hence, we expect that this work will add an aspect to random lasers by using metal nanostructures to obtain coherent feedback.

/pdf/random-lasers-with-coherent-feedback-from-highly-transparent-2jtnoei808.pdf

Random lasers with coherent feedback from highly transparent polymer films embedded with silver nanoparticles

Theoretical calculations of Zn $K$ and Fe $K$ x-ray absorption near-edge structures (XANES) using a first-principles method have been performed to evaluate the degree of cation disordering in spinel zinc ferrite $(\mathrm{Zn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4})$ thin film prepared by a sputtering method, $\mathrm{Zn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ thin films annealed at elevated temperatures, and $\mathrm{Zn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ bulk specimen prepared by a solid-state reaction. Using the full-potential linearized augmented plane-wave + local orbitals method, a theoretical spectrum is generated for the tetrahedral and octahedral environments for each of the two cations. The experimental XANES spectrum of the thin film annealed at $800\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ as well as that of bulk specimen is successfully reproduced by using either the theoretical spectrum for ${\mathrm{Zn}}^{2+}$ on the tetrahedral site ($A$ site) or that for ${\mathrm{Fe}}^{3+}$ on the octahedral site ($B$ site), which is indicative of the normal spinel structure. For the as-deposited film, on the other hand, excellent agreement between theoretical and experimental spectra is obtained by considering the presence of either ion in both the $A$ and $B$ sites. The degree of cation disordering, $x$, defined as ${[\mathrm{Zn}_{1\ensuremath{-}x}{}^{2+}\mathrm{Fe}_{x}{}^{3+}]}_{A}{[\mathrm{Zn}_{x}{}^{2+}\mathrm{Fe}_{2\ensuremath{-}x}{}^{3+}]}_{B}{\mathrm{O}}_{4}$, is estimated to be approximately 0.6 in the as-deposited film, which is consistent with the analysis of the extended x-ray absorption fine structure on the Zn $K$ edge. Curious magnetic properties as we previously observed for the as-deposited thin film---i.e., ferrimagnetic behaviors accompanied by large magnetization at room temperature and cluster spin-glass-like behavior---are discussed in connection with disordering of ${\mathrm{Zn}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ ions in the spinel-type structure.

/pdf/first-principles-xanes-simulations-of-spinel-zinc-ferrite-vlw5o1spaf.pdf

First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution

Large-scale battery systems are essential for efficiently utilizing renewable energy power sources from solar and wind, which can generate electricity only intermittently. The use of lithium-ion batteries to store the generated energy is one solution. A long cycle life is critical for lithium-ion battery when used in these applications; this is different from portable devices which require 1,000 cycles at most. Here we demonstrate a novel co-substituted lithium iron phosphate cathode with estimated 70%-capacity retention of 25,000 cycles. This is found by exploring a wide chemical compositional space using density functional theory calculations. Relative volume change of a compound between fully lithiated and delithiated conditions is used as the descriptor for the cycle life. On the basis of the results of the screening, synthesis of selected materials is targeted. Single-phase samples with the required chemical composition are successfully made by an epoxide-mediated sol-gel method. The optimized materials show excellent cycle-life performance as lithium-ion battery cathodes.

/pdf/accelerated-discovery-of-cathode-materials-with-prolonged-tvwbl83sax.pdf

Accelerated discovery of cathode materials with prolonged cycle life for lithium-ion battery

We experimentally demonstrate the capability of tailoring lasing resonance properties by manipulating the coupling between surface plasmons and photons in random lasing media composed of metallic−dielectric core−shell nanoparticles and organic dyes. It is revealed that core−shell nanoparticle-based systems exhibit optical feedback features distinctive from those containing pure metallic nanoparticles, provided that the scattering strength is weak enough. The pump threshold increases with an increment in the shell thickness, which can provide a direct proof that the local field enhancement plays a central role in the emergence of coherent feedback. The anomalous behavior in both threshold and optical feedback is discussed in terms of the modification of fluorescent properties of fluorophores close to metallic surface.

Katsuhisa Tanaka

Papers

Wavelength-tunable spasing in the visible.

Random lasers with coherent feedback from highly transparent polymer films embedded with silver nanoparticles

First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution

Accelerated discovery of cathode materials with prolonged cycle life for lithium-ion battery

Plasmonically controlled lasing resonance with metallic-dielectric core-shell nanoparticles.