Atsunobu Masuno

Multiferroic thin film of Bi2NiMnO6 with ordered double-perovskite structure

Epitaxial thin films of Bi2NiMnO6 were synthesized on SrTiO3 substrates by pulsed laser deposition. The resulting film had the rock-salt-type arrangement of Ni2+ and Mn4+ ions in a double-perovskite unit cell. The films clearly showed multiferroic properties, both ferromagnetic behavior with a Curie temperature of about 100K and ferroelectric behavior with a saturated polarization of about 5μC∕cm2.

Epitaxial growth of ferromagnetic La2NiMnO6 with ordered double-perovskite structure

Epitaxial thin films of ordered double-perovskite La2NiMnO6 were deposited on SrTiO3, (LaAlO3)0.3–(Sr2AlTaO6)0.7, and LaAlO3 substrates by a pulsed-laser deposition method. A rock-salt-type ordering for Ni2+ and Mn4+ ions was confirmed through structural and magnetic measurements. Despite the difference in heteroepitaxial constraints on the crystal structure, the magnetic properties of the films were quite similar to each other and also to those of bulk La2NiMnO6.

Refractive index dispersion, optical transmittance, and Raman scattering of BaTi2O5 glass

The optical and vibrational properties of BaTi2O5 glass prepared by containerless processing were investigated. The refractive index was 2.15 and the Abbe number was 21.5, as measured by the focal method. The glass was transparent from 340 nm to 7.7 μm. From the Raman scattering spectrum, the maximum phonon energy was found to be 829 cm−1. Using these data, fundamental optical parameters such as the optical basicity, the average oscillator strength, and the optical band gap were estimated. These parameters suggest that BaTi2O5 glass is an attractive material with many potential applications such as lenses, windows, nonlinear optics, and phosphors; moreover, these parameters can guide future development of new titanate glass compositions with superior optical properties.

Topological engineering of glass for modulating chemical state of dopants.

A novel approach to modulating the chemical state of dopants by engineering the topological features of a glass matrix is presented. The method allows selective stabilization of dopants on a wide range of length scales, from dispersed ions to aggregated clusters to nanoparticles, leading to various intriguing optical phenomena, such as great emission enhancement and ultra-broadband optical amplification.

High Refractive Index of 0.30La2O3–0.70Nb2O5 Glass Prepared by Containerless Processing

A high-refractive-index glass with the composition of 0.30La2O3–0.70Nb2O5 was prepared in bulk form by containerless processing without using network former oxides. The glass transition temperature was 725 °C and the first crystallization peak temperature was 805 °C. The glass was colorless and transparent from 345 nm to 7.3 µm. The refractive index was higher than 2.3 in the visible range, and the Abbe number estimated from the Drude–Voigt relationship was 20.4. These results indicate that the niobate glass system would be useful for optical applications in the visible to infrared region.

High Elastic Moduli of a 54Al2O3-46Ta2O5 Glass Fabricated via Containerless Processing.

Glasses with high elastic moduli have been in demand for many years because the thickness of such glasses can be reduced while maintaining its strength. Moreover, thinner and lighter glasses are desired for the fabrication of windows in buildings and cars, cover glasses for smart-phones and substrates in Thin-Film Transistor (TFT) displays. In this work, we report a 54Al2O3-46Ta2O5 glass fabricated by aerodynamic levitation which possesses one of the highest elastic moduli and hardness for oxide glasses also displaying excellent optical properties. The glass was colorless and transparent in the visible region, and its refractive index nd was as high as 1.94. The measured Young’s modulus and Vickers hardness were 158.3 GPa and 9.1 GPa, respectively, which are comparable to the previously reported highest values for oxide glasses. Analysis made using 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy revealed the presence of a significantly large fraction of high-coordinated Al in addition to four-coordinated Al in the glass. The high elastic modulus and hardness are attributed to both the large cationic field strength of Ta5+ ions and the large dissociation energies per unit volume of Al2O3 and Ta2O5.

Noncentrosymmetric Structure of LuFeO3 in Metastable State

The crystal structure of metastable LuFeO3 synthesized by containerless processing has been revealed to be a non-centrosymmetric structure (space group P63cm) by analyzing the high-energy synchrotron-radiation powder-diffraction data using the maximum entropy method (MEM)/Rietveld method. The structural characteristics are found in the FeO5 trigonal bipyramid distorted and tilted from the c-axis, which is cause by the hybridization of atomic orbitals between the O atom constituent of the polyhedron and the neighboring Lu atom. The spontaneous polarization expected from the polar structure is estimated at about 5 µC/cm2.

Crack-resistant Al2O3–SiO2 glasses

Obtaining “hard” and “crack-resistant” glasses have always been of great important in glass science and glass technology. However, in most commercial glasses both properties are not compatible. In this work, colorless and transparent xAl2O3–(100–x)SiO2 glasses (30 ≤ x ≤ 60) were fabricated by the aerodynamic levitation technique. The elastic moduli and Vickers hardness monotonically increased with an increase in the atomic packing density as the Al2O3 content increased. Although a higher atomic packing density generally enhances crack formation in conventional oxide glasses, the indentation cracking resistance increased by approximately seven times with an increase in atomic packing density in binary Al2O3–SiO2 glasses. In particular, the composition of 60Al2O3•40SiO2 glass, which is identical to that of mullite, has extraordinary high cracking resistance with high elastic moduli and Vickers hardness. The results indicate that there exist aluminosilicate compositions that can produce hard and damage-tolerant glasses.

Modeling of the Structure of Sodium Borosilicate Glasses Using Pair Potentials

Structural models of sodium borosilicate glasses were prepared by means of molecular dynamics (MD) technique using pair potentials over a wide compositional range. The local structures around B, O, and Si obtained from the structural models were compared with experimental (11)B NMR, (17)O NMR, and (29)Si NMR data. It was found that atomic arrangements of B, O, and Si in the structural models were similar to the experimental results indicating that the simulations can reproduce the chemical bonds of the real glasses. These results confirm that even if the MD technique using the pair potentials is quite simple, it is enough to capture the essence of the amorphous materials. In the linkage of the cation-oxygen polyhedra, the differences were observed between the structural models and the experimental results. The factors responsible for these differences are discussed with respect to the equilibrium reactions between the cation-oxygen polyhedra at a higher temperature. The discussion suggests that the differences were caused by the extremely higher quenching rate than the real glasses as well as by the simplicity of our pair potential and the smaller size of the unit cell.

Atomic and electronic structures of an extremely fragile liquid

The structure of high-temperature liquids is an important topic for understanding the fragility of liquids. Here we report the structure of a high-temperature non-glass-forming oxide liquid, ZrO2, at an atomistic and electronic level. The Bhatia–Thornton number–number structure factor of ZrO2 does not show a first sharp diffraction peak. The atomic structure comprises ZrO5, ZrO6 and ZrO7 polyhedra with a significant contribution of edge sharing of oxygen in addition to corner sharing. The variety of large oxygen coordination and polyhedral connections with short Zr–O bond lifetimes, induced by the relatively large ionic radius of zirconium, disturbs the evolution of intermediate-range ordering, which leads to a reduced electronic band gap and increased delocalization in the ionic Zr–O bonding. The details of the chemical bonding explain the extremely low viscosity of the liquid and the absence of a first sharp diffraction peak, and indicate that liquid ZrO2 is an extremely fragile liquid.