The layered chalcogenide Ta2NiSe5 has recently attracted much interest as a strong candidate for the long sought excitonic insulator (EI). Since the physical properties of an EI are expected to depend sensitively on the external pressure, it is important to clarify the pressure evolution of microscopic electronic state in Ta2NiSe5. Here we report the optical conductivity [s(w)] of Ta2NiSe5 measured at high pressures to 10 GPa and at low temperatures to 8 K. With cooling at ambient pressure, s(w) develops an energy gap of about 0.17 eV and a pronounced excitonic peak at 0.38 eV, as already reported in the literature. Upon increasing pressure, the energy gap becomes narrower and the excitonic peak is broadened. Above a structural transition at Ps~3 GPa, the energy gap becomes partially filled, indicating that Ta2NiSe5 is a semimetal after the EI state is suppressed by pressure. At higher pressures, s(w) exhibits metallic characteristics with no energy gap. The detailed pressure evolution of s(w) is presented, and discussed mainly in terms of a weakening of excitonic correlation with pressure.

1Gradute Faculty of Interdisciplinary Research, University of Yamanashi, 4–4–37 Takeda, Kofu 400–8510, Japan 2National Institute for Materials Science (NIMS), 1–2–1 Sengen, Tsukuba, Ibaraki 305–0047, Japan 3Materials Research Center for Element Strategy, Tokyo Institute of Technology, 4259-SE-6 Nagatsuta-cho, Midori-ku, Yokohama 226–8501, Japan 4Graduate School of Advanced Science and Engineering, Hiroshima University, Higashihiroshima, Hiroshima 739–8526, Japan

The development of transparent glass for use in high-temperature applications is continuing. In this study, we synthesized bulk silicon oxynitride glasses (a-Si(O,N)(x)) through the nitridation of SiO2 aerogels containing methyl (CH3-) groups and evaluated their bulk properties, including their glass transition temperature (T-g). Tetramethyl orthosilicate and methyltrimethoxysilane were added into the precursor gels, and those gels were subjected to a supercritical CO2 drying process. The presence of CH3-group in the gel avoided cracking during ammonolysis at 750 degrees C-1400 degrees C, and the transparency of the gel was remained even after ammonolysis at 1300 degrees C. The ammonolysis successfully introduced nitrogen into the gels even at relatively low temperatures, for example, 750 degrees C, and the highest nitrogen content (11.7 mass%) was achieved in the gel after ammonolysis at 1300 degrees C. As the nitrogen-related signals in electron spectroscopy indicated presence of nitride ions (N3-) after ammonolysis and the infrared absorption signals attributed to Si-N bonds were enhanced with the increase of nitrogen concentration, we successfully obtained oxynitride glasses. Those oxynitride glasses showed increase of T-g with their nitrogen concentration.

In this study, we investigated chemothermal pulverization (CTP) phenomena that are induced in titanate single crystals and ceramics by high-temperature treatment at approximately 1000celcius under reactive gas containing ammonia and oxygen and cause these materials to break down into nanosized powders. Structural characterization revealed that there were many nanosized voids formed in titanates during heat treatment for CTP, and subsequent analysis revealed that these voids were filled with nitrogen gas. These results indicated that CTP consisted of four steps: the in-diffusion of nitride ions from the surface to titanates, the deposition of nitrogen molecules (gas) inside the titanate crystals instead of nitride formation, the growth of voids by further nitrogen transport from the surface to voids, and, finally, the breakdown of the walls between voids to form nanopowders. Furthermore, we discussed the exact mechanism of CTP phenomena by examining the effect of doping into titanates on the progress of CTP and by conducting theoretical calculations for the simulation of nitrogen impurities in titanate lattices.

A novel UV-Vis photodetector consisting of an octahedral molybdenum cluster-functionalized Zn2Al layered double hydroxide (LDH) has been successfully synthesized by co-precipitation and delamination methods under ambient conditions. The electrophoretic deposition process has been used as a low cost, fast, and effective method to fabricate thin and transparent nanocomposite films containing a dense and regular layered structure. The study provided evidence that the presence of the Mo6 cluster units between the LDH does not affect the ionic conduction mechanism of the LDH, which linearly depends on the relative humidity and temperature. Moreover, the photocurrent response is remarkably extended to the visible domain. The reproducibility and stabilization of the photocurrent response caused by the Mo6 cluster-functionalized LDH have been verified upon light excitation at 540 nm. Additionally, it was demonstrated that the films show advantageously strong adherence properties for application requirements.

A new layered double hydroxide (LDH)-based nanocomposite functionalized with an octahedral molybdenum atom cluster (MC) exhibiting prominent photoactive and oxidation properties was synthesized. Zn-Al LDH and Zn-Al LDH intercalated dodecyl sulfate compounds (abbreviated as LDH-1 and LDH-2 respectively) were prepared by the co-precipitation method in an aqueous solution. The MCs were simply introduced into the LDH-2 by an anion exchangeable method in dimethylformamide under ambient conditions. The extension of the basal spacing of the LDH-1 from 0.9 nm to about 5 nm by intercalating dodecyl sulfate and Mo-6 cluster was confirmed by several complementary technics. The octahedral structure of the Mo-6 cluster was retained on the outer surface between big nanosheets (NSs) and inner surface between the single layers that were confirmed by ultraviolet-visible absorption and photoluminescence experiments. The possible chemical bonding between the [(Mo6Cl8Cl6-x-ya)-Cl-i(H2O)(x)(a)(OH)(y)(a)](x-2) (x = 0, 1 or 2 and y = 0, 1, 2, 3; x + y = 3) clusters and LDH-2 was suggested on the basis of by X-ray photoelectron spectroscopy. The excellent photoactive and oxidation performance of the Mo-6 cluster on the methylene blue degradation in an aqueous solution was determined in the dark, under UV light (lambda = 370 nm) or with the existence of H2O2. The combination of the LDH-2 with a high absorbability and recyclability and the Mo-6 cluster will be a promising candidate as a heterogenized homogeneous catalyst for removing organic pollutants.

We investigated the multiscale characters of the crystal structure of the oxynitride perovskite LaTiO2N. While X-ray diffraction results identified the average structure as being centrosymmetric, we detected a signature of unknown structural deformation. By viewing the local structure, we unveiled the formation of a polar structure at the nanoscale.

Transition metal nitrides (TMN) form a class of materials with unique physical and chemical properties. Among them, molybdenum nitrides are mainly used as high-performance magnets or catalysts for a wide range of reactions. This work aims at developing innovative syntheses to prepare nanostructured TMN from metallic clusters for heterogeneous catalysis. The use of a nanoscale precursor such as (TBA)(2) Mo6Br14 (TBA = tetrabutylammonium = (C4H9)(4)N+) enables us to reach different molybdenum nitride compositions (Mo2N, Mo5N6) by thermal reaction under ammonia at relatively low temperatures. Such a novel synthetic approach highlights the prime importance of the starting material to stabilize specific stoichiometries. The impact of this new synthetic route is characterized by several techniques including electron probe microanalysis and high-resolution transmission microscopy. Moreover,catalytic properties of these potential cost-effective catalysts are investigated for the Water-Gas Shift Reaction.

The nanoparticle-based material technology has recently opened a new heat shielding material generation for window applications such as aerogel, vacuum insulation panel or nanospace materials. Aiming to prepare a nanospace-based heat insulation material functionalized with an ultraviolet (UV) absorbent, the Mo-6 cluster-deposited hollow silica nanoparticles (HSNs) were prepared by the vacuum impregnation process (VIP). The pore channels of the hollow silica wall filled with the Cs-2[Mo6I8i(OCOC2F5)(6)(a)] octahedral cluster (CMIF) were confirmed by an HR-TEM coupled EDX device, ICP-OES and BET analysis. The retention of the octahedral structure or the typical optical property of the Mo-6 cluster in the pores of the HSNs was demonstrated by ultraviolet (UV) light absorption and photoluminescence spectroscopes even though the powders were heated to 200 degrees C. The multi-functional CMIF@HSNs nanocomposite could adsorb the UV rays under 400 nm and scatter the NIR light through the pores of the silica wall in order to reduce the heat passing a window. For this purpose, the film preparation based on the CMIF@HSNs nanocomposite was performed by dip coating in the commercially available top coat suspension (TCS) on soda lime glass. Excellent mechanical and optical properties of the CMIF@HSNs-based thin film were visibly obtained with a relative transmittance. This study suggests a potential insulation material prepared by a high efficiency and simple method for reducing the air temperature in buildings. (C) 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan.

Manganese oxide particles were prepared by alkaline treatment of the manganese and silicon compound. Silicon was selectively dissolved by the alkaline treatment, forming an aggregate structure of plate-like particles. Consequently, owing to the high specific surface area and surface exposure of the manganese, the catalyst exhibited excellent behavior in the oxidative decomposition of benzene. (C) 2020 The Ceramic Society of Japan. All rights reserved.

Hexanuclear tantalum bromide cluster units [{Ta6Bri12}La6] (i = inner, a = apical, L = ligand OH or H2O) are embedded into SiO2 nanoparticles by a reverse microemulsion (RM) based method. [{Ta6Bri12}Bra2 (H2O)a4]·nH2O (noted TBH) and tetraethyl orthosilicate (TEOS) are used as the starting cluster compound and the precursor of SiO2, respectively. The RM system in this study consists of the n-heptane (oil phase), Brij L4 (surfactants), ethanol, TEOS, ammonia solution and TBH aqueous sol. The size and morphology of the product namely {Ta6Br12}@SiO2 nanoparticles are analyzed by HAADF-STEM and EDS mappings. The presence and integrity of {Ta6Br12} in the SiO2 nanoparticles are evidenced by EDS mapping, ICP-OES/IC and XPS analysis. The optical properties of {Ta6Br12}@SiO2 nanoparticles are analyzed by diffuse reflectance UV-vis spectroscopy, further evidencing the integrity of the embedded {Ta6Br12} and revealing their oxidation state. Both {Ta6Br12}2+ and {Ta6Br12}3+ are found in SiO2 nanoparticles, but the latter is much more stable than the former. The by-products in this RM-based synthesis, as well as their related factors, are also discussed.

NO3-type Zn/Al layered double hydroxides were synthesized by co-precipitation method. The interlayers of the layered double hydroxides were highly expanded by intercalating laurate ions by ion exchange to get it easier to distinguish each layer of the layered double hydroxides by high-resolution transmission electron microscopy observation. Direct observation of the stacking faults in the expanded LDH was successfully carried out by intercalating the laurate ions. The expanded LDH exhibited photoluminescence under the irradiation of 325 nm UV light. (C) 2017 Elsevier B.V. All rights reserved.

The present report describes the catalytic activity of mechanically activated nano quasicrystalline Al65Cu20Fe15 and related nano crystalline Al50Cu28Fe22 for the synthesis of carbon nanotubes (CNTs). CNTs are synthesized by catalytic decomposition of ethanol through nano quasicrystalline Al65Cu20Fe15 and related crystalline Al50Cu28Fe22 alloys as a catalyst. The synthesized multi-walled CNTs exhibits tube diameter ranging from 5 to 25 nm. The synthesized CNTs are characterized by scanning and transmission electron microscopy. It is found that Al65Cu20Fe15 nanoquasicystal shows better catalytic behaviour as compared to nano-crystalline Al50Cu28Fe22 alloys for decomposition of ethanol during the synthesis of multi-walled CNTs.

NaCl-type (B1) chromium oxide (CrO) has been expected to have a high hardness value and does not exist as an equilibrium phase. We report a B1-based Cr0.67O thin film with a thickness of 144 nm prepared by pulsed laser deposition as an epitaxial thin film on a MgO single crystal. The thin film contained a number of stacking faults and had a nanotwinned structure composed of B1 with disordered vacancies and corundum structures. The Cr0.67O thin film had a high indentation hardness value of 44 GPa, making it the hardest oxide thin film reported to date.

The magnetic skyrmion is a topologically stable spin texture in which the constituent spins point to all the directions wrapping a sphere. Generation and control of nanometric magnetic skyrmions have large potential, for example, reduced power consumption, in spintronics device applications. Here we show the real-space observation of a biskyrmion, as defined by a molecular form of two bound skyrmions with the total topological charge of 2, realized under magnetic field applied normal to a thin plate of a bilayered manganite with centrosymmetric structure. In terms of a Lorentz transmission electron microscopy (TEM), we have observed a distorted-triangle lattice of biskyrmion crystal, each composed of two bound skyrmions with oppositely swirling spins (magnetic helicities). Furthermore, we demonstrate that these biskyrmions can be electrically driven with orders of magnitude lower current density (<10(8) A m(-2)) than that for the conventional ferromagnetic domain walls.

Chirality--that is, left- or right-handedness--is an important concept in a broad range of scientific areas. In condensed matter, chirality is found not only in molecular or crystal forms, but also in magnetic structures. A magnetic skyrmion is a topologically stable spin vortex structure, as observed in chiral-lattice helimagnets, and is one example of such a structure. The spin swirling direction (skyrmion helicity) should be closely related to the underlying lattice chirality via the relativistic spin-orbit coupling. Here, we report on the correlation between skyrmion helicity and crystal chirality in alloys of helimagnets Mn(1-x)Fe(x)Ge with varying compositions by Lorentz transmission electron microscopy and convergent-beam electron diffraction over a broad range of compositions (x = 0.3-1.0). The skyrmion lattice constant shows non-monotonous variation with composition x, with a divergent behaviour around x = 0.8, where the correlation between magnetic helicity and crystal chirality changes sign. This originates from continuous variation of the spin-orbit coupling strength and its sign reversal in the metallic alloys as a function of x. Controllable spin-orbit coupling may offer a promising way to tune skyrmion size and helicity.

We investigated the crystal structures of an ordered perovskite-type cobaltate, GdBaCo2O(5+δ) (δ < 0.5), at elevated temperatures by transmission electron microscopy. Above the magnetic ordering temperature, we observed a first-order structural phase transition between the low-temperature tetragonal 3a(p) × 3a(p) and high-temperature orthorhombic 1a(p) × 2a(p) superstructure phases (where a(p) is the perovskite-unit cell). Upon the application of a magnetic field, an incommensurate phase emerges around the structural phase-transition temperature, which indicates a magnetic-field-induced structural phase transition via no magnetic ordering in the ordered perovskite-type cobaltate.