Tomohiko Nakajima

Direct fabrication of metavanadate phosphor films on organic substrates for white-light-emitting devices

White-light-emitting materials have attracted considerable attention because of their applications, such as large-surface emitting devices. Inorganic phosphor films are expected to be applied to these devices because of good chemical stability; however, a substantial reduction of fabrication temperature is required for future industrial uses such as lighting materials fabricated onto flexible organic substrates. Here we show the optical properties of white-light-emitting metavanadate phosphors, AVO3 (A: K, Rb and Cs), and we report a new direct fabrication process for RbVO3 films onto flexible polyethylene terephthalate (PET) substrates by means of a vacuum ultraviolet irradiation using an excimer lamp. In addition, the (Ca,Sr,Pr)TiO3/a-Al2O3/RbVO3/PET heterostructure prepared by an excimer-laser-assisted metal-organic deposition process has demonstrated the possibility of colour modification for RbVO3 films on PET. Our findings suggest new possibilities for further development of large-surface emitting lighting devices.

Black TiO2 nanotubes formed by high energy proton implantation show noble-metal-co-catalyst free photocatalytic H2-evolution

We apply high-energy proton ion-implantation to modify TiO2 nanotubes selectively at their tops. In the proton-implanted region, we observe the creation of intrinsic cocatalytic centers for photocatalytic H2-evolution. We find proton implantation to induce specific defects and a characteristic modification of the electronic properties not only in nanotubes but also on anatase single crystal (001) surfaces. Nevertheless, for TiO2 nanotubes a strong synergetic effect between implanted region (catalyst) and implant-free tube segment (absorber) can be obtained.

Structures and Electromagnetic Properties of New Metal-Ordered Manganites: RBaMn2O6 (R=Y and Rare-Earth Elements)

New metal-ordered manganites R BaMn 2 O 6 can be classified into three groups based on the structural and electromagnetic properties measured. The first group ( R =Tb, Dy and Ho) shows three succes...New metal-ordered manganites R BaMn 2 O 6 can be classified into three groups based on the structural and electromagnetic properties measured. The first group ( R =Tb, Dy and Ho) shows three successive phase transitions, namely, structural, charge/orbital order (CO) and antiferromagnetic order (AF) transitions on cooling, as observed in YBaMn 2 O 6 . The second group ( R =Sm, Eu and Gd) exhibits a CO transition, followed by an AF transition. The third group ( R =La, Pr and Nd) exhibits a metallic ferromagnetic transition, followed by an A -type AF transition in PrBaMn 2 O 6 and NdBaMn 2 O 6 . Compared with metal-disordered ( R 0.5 3+ A 0.5 2+ )MnO 3 , R BaMn 2 O 6 has two remarkable features: (1) the high CO transition temperature ( T CO ) above 340 K and (2) the presence of a structural transition above T CO in the first group. These are closely related to the structural feature that the MnO 2 sub-lattice is sandwiched by two types of rock-salt layers, R O and BaO, with different lattice sizes.

New A-site Ordered Perovskite Cobaltite LaBaCo2O6: Synthesis, Structure, Physical Property and Cation Order–Disorder Effect

By means of annealing LaBaCo 2 O 5 under high pressure oxygen, we have successfully synthesized a new A-site ordered perovskite cobaltite, LaBaCo 2 O 6 . The structure and electromagnetic propertie...

A-site Randomness Effect on Structural and Physical Properties of Ba-based Perovskite Manganites

The discovery of novel structural and physical properties in the A -site ordered manganite R BaMn 2 O 6 ( R = Y and rare earth elements) has demanded new comprehension about perovskite manganese ox...

Successive phase transitions in a metal-ordered manganite perovskite YBaMn2O6

Abstract Structural, magnetic and electric properties of a metal-ordered perovskite YBaMn 2 O 6 have been studied by means of powder X-ray diffraction, differential scanning calorimetric, magnetic susceptibility, and electric resistivity. It is found that this material undergoes a first-order structural phase transition at T c 1 =520 K , from a pseudo orthorhombic (monoclinic) phase ( T c1 T ) to a pseudo tetragonal (monoclinic) one ( T T c1 ). Accompanied by this transition the susceptibility exhibits a sharp drop where ferromagnetic exchange interaction becomes antiferromagnetic. Furthermore, two more transitions, a metal–insulator transition at T c 2 =480 K and an antiferromagnetic ordering at T c 3 =200 K , have been observed, respectively.

Ground State Properties of the A-site Ordered Manganites, RBaMn2O6 (R = La, Pr and Nd)

The most significant structural feature of the A -site ordered manganese perovskites, R BaMn 2 O 6 , is that the MnO 2 square sublattice is sandwiched by two types of rock-salt layers, R O and BaO,...

Hydrogenated Anatase: Strong Photocatalytic Dihydrogen Evolution without the Use of a Co-Catalyst†

The high-pressure hydrogenation of commercially available anatase or anatase/rutile TiO2 powder can create a photocatalyst for H2 evolution that is highly effective and stable without the need for any additional co-catalyst. This activation effect cannot be observed for rutile; however, for anatase/rutile mixtures, a strong synergistic effect can be found (similar to results commonly observed for noble-metal-decorated TiO2). EPR and PL measurements indicated the intrinsic co-catalytic activation of anatase TiO2 to be due to specific defect centers formed during hydrogenation. These active centers can be observed specifically for high-pressure hydrogenation; other common reduction treatments do not result in this effect.

Novel structures and electromagnetic properties of the A-site-ordered/disordered manganites RBaMn2O6/R0.5Ba0.5MnO3 (R = Y and rare earth elements)

The A-site-ordered/disordered manganese perovskites, RBaMn 2 O 6 /R 0.5 Ba 0.5 MnO 3 (R = Y and rare earth elements), are reviewed. RBaMn 2 O 6 displays remarkable features: (1) the charge/orbital order (CO) transition at relatively high temperatures far above 300 K, (2) a new stacking variation of the CE-type CO with a fourfold periodicity along the c-axis, (3) the presence of structural transition possibly accompanied by d x 2 -y 2 orbital order and (4) electronic phase segregation. These novel structural and electromagnetic properties are discussed in terms of the structural characteristic that the MnO 2 square sublattice is sandwiched by two types of rock-salt layer, RO and BaO, with different lattice sizes. Such structure introduces a strong frustration to the MnO 2 sublattice and gives a new perturbation to the competition of multiple degrees of freedom among charge, orbital, spin and lattice. In R 0.5 Ba 0.5 MnO 3 with a primitive cubic perovskite cell, on the other hand, the magnetic glassy states are dominant as the ground state. A peculiar behaviour, steplike ultrasharp magnetization and resistivity changes, has been observed in Pr 0.5 Ba 0.5 MnO 3 .

New Stacking Variations of the Charge and Orbital Ordering in the Metal-Ordered Manganite YBaMn2O6

We performed transmission electron microscopy (TEM) and powder neutron diffraction experiments on an A -site ordered manganese perovskite YBaMn 2 O 6 which undergoes unusual and multiple phase transitions. In the paramagnetic insulating phase, the so-called CE type of charge and orbital ordering was observed in the monoclinic a – b plane, which has been frequently observed for the ordinary solid solution of A 1- x 3+ A x ′2+ MnO 3 around x =0.5. TEM revealed, however, a fourfold periodicity along the c axis, suggesting a new stacking pattern, in which planes of the CE type are built up according to the sequence [ααββ...]. Interestingly, when the system entered the antiferromagnetic state below 195 K, this stacking pattern changed into [αααα...] or [αβαβ...], suggesting a close interplay between spins and orbitals. The obtained stacking patterns were strongly correlated to the inherent structural alternation, i.e., the Y/Ba order along the c axis.