Yoshio Matsui

New layered manganite LaSr₂Mn₂O₇ is prepared, and examined by HRTEM and by low-temperature electron diffraction to examine the possibility of charge- and orbital-ordered states occuring below 200K. The crystal structure of this layered manganites is almost perfect and no planar or intergrowth defects has been detected by HRTEM. At low temperature of 200K-110K, hk0 electron diffraction patterns clearly exhibit the appearances of characteristic super-reflection spots along the a*+b* direction. The superstructure is interpreted in terms of the Mn³⁺/Mn⁴⁺ charge-ordering, associated with dz2https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003063056/c87f8d57-bd6e-40f8-a651-90760b6f3961/content/ieq0155.tif"/> orbital-ordering to induce Jahn-Teller distortion around the Mn³⁺ ions.

In this study, we investigated chemothermal pulverization (CTP) phenomena that are induced in titanate single crystals and ceramics by high‐temperature treatment at approximately 1000℃ 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.

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 SiO ₂ aerogels containing methyl (CH ₃ ‐) 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 CO ₂ drying process. The presence of CH ₃ ‐group in the gel avoided cracking during ammonolysis at 750°C–1400°C, and the transparency of the gel was remained even after ammonolysis at 1300°C. The ammonolysis successfully introduced nitrogen into the gels even at relatively low temperatures, for example, 750°C, and the highest nitrogen content (11.7 mass%) was achieved in the gel after ammonolysis at 1300°C. As the nitrogen‐related signals in electron spectroscopy indicated presence of nitride ions (N ³⁻ ) 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.

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.

Polar nano-region formation in the oxynitride perovskite LaTiO₂N is demonstrated from PDF analysis.

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 Cr_0.67O 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 Cr_0.67O 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 (8 A m⁻²) than that for the conventional ferromagnetic domain walls.