Showing papers by "Shigeo Mori published in 2014"
TL;DR: In this article, a cubic A-site ordered perovskite oxide LaCu3Fe4−xMnxO12 was shown to achieve negative and zero thermal expansion near room temperature.
Abstract: Negative and zero thermal expansion near room temperature have been achieved in a cubic A-site ordered perovskite oxide LaCu3Fe4−xMnxO12. A discontinuous volume change in the parent material LaCu3Fe4O12, owing to a first-order intermetallic charge transfer transition (3Cu2+ + 4Fe3.75+ ⇄ 3Cu3+ + 4Fe3+), is efficiently relaxed to a second-order-type negative thermal expansion with a linear thermal expansion coefficient (αL) of −2.2(1) × 10−5 K−1 between 300 and 340 K at x = 0.75, followed by an almost zero thermal expansion [αL of −1.1(2) × 10−6 K−1] at x = 1 in a wide temperature range (240–360 K) including room temperature. Magnetic susceptibility measurements display substantial broadenings of the antiferromagnetic transition when x increases, supporting the relaxation of first-order electronic phase transition of the parent material. These findings indicate that the significant adjustability of thermal expansion properties can be achieved in first-order intermetallic charge-transfer transition.
28 citations
TL;DR: The findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu3Fe 4O12 series and that the melting of the charge-ordering in CeCu2Fe3Fe2O12 is caused by the substantial decrease in the Fe valence and the resulting large deviation from the ideal abundance ratio of Fe(3+):Fe(5+) = 1:1 for rock-salt-type charge- ordering.
Abstract: A novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. 57Fe Mossbauer spectroscopy displays a charge disproportionation transition of 4Fe3.5+ → 3Fe3+ + Fe5+ below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured. Electron and X-ray diffraction studies reveal that the body-centered cubic symmetry (space group Im3, No. 204) is retained at temperatures as low as 100 K, indicating the absence of any types of charge-ordering in the charge-disproportionated CeCu3Fe4O12 phase. The magnetic susceptibility and neutron powder diffraction data illustrate that the antiferromagnetic ordering of Fe ions is predominant in the charge-disproportionated CeCu3Fe4O12 phase. These findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu...
25 citations
TL;DR: In this article, the atomic shifts of Y3+ and Mn3+ (Ti4+) in hexagonal YMn1-xTixO3-δ domains and domain wall structures at the atomic scale were investigated by using aberration-corrected high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) experiments, combining with the conventional TEM observation techniques.
Abstract: We have investigated ferroelectric (FE) and structural antiphase (SAP) domains and domain wall structures at the atomic scale in hexagonal YMn1-xTixO3-δ by using aberration-corrected high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) experiments, combining with the conventional TEM observation techniques. Atomic shifts of Y3+ and Mn3+ (Ti4+) in the FE and SAP domains and domain wall structures in YMn1-xTixO3-δ are successfully visualized at the atomic scale. When Ti4+ are substituted for Mn3+, the magnitude of the shifts of Y3+ is reduced and the regions without any displacement of Y3+ along the [001] direction dominated around x-0.40. Our experimental results clearly revealed that partial substitution of Ti4+ for Mn3+ suppress the magnitude of the shifts of Y3+ ions along the [001] direction and the FE properties tend to diminish with increasing the amount of Ti4+ in YMn1-xTixO3-δ.
10 citations
TL;DR: The combination of the temperature increase and light irradiation was shown to control their interaction with cells, enabling selective cell killing by the AuNP-hybridized temperature-sensitive dendrimers.
Abstract: Stimuli-sensitive dendrimers of a new type were developed through dual functionalization of polyamidoamine (PAMAM) dendrimers with temperature-sensitive surface modification using propoxy diethylene glycol (PDEG) and Au nanoparticle (AuNP) loading. These AuNP-hybridized dendrimers were prepared by attaching PDEG to amine-terminated PAMAM G5 dendrimer using 4-nitrophenylchloroformate and subsequent loading of AuNPs into the dendrimer interior via reduction of AuCl4− ions with NaBH4 in the dendrimer interior. Transmission electron microscopy showed that AuNPs with diameters of about 2 nm were retained in the PDEG-modified dendrimers. These AuNP-loaded dendrimers were dissolved in aqueous solutions at low temperature but became water-insoluble above a specific temperature, because of the character change of the dendrimer surface from hydrophilic to hydrophobic depending on temperature. The AuNPs in the dendrimer interior generated heat under irradiation by a green laser and hence, their association could be induced in the specific area irradiated with the green laser. In addition, the combination of the temperature increase and light irradiation was shown to control their interaction with cells, enabling selective cell killing by the AuNP-hybridized temperature-sensitive dendrimers.
7 citations
TL;DR: In this article, a structural phase boundary exists at approximately x = 0.6 between the P63 structure with a large structural fluctuation and a monoclinic P21 phase with the single-q modulated structure.
Abstract: Crystal structures and microstructures in Ba1−xSrxAl2O4 solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent 〈110〉 directions in the (001) plane, which appear in the P63 structure of Ba1−xSrxAl2O4 for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P21 structure in Ba1−xSrxAl2O4 with x = 0.7 was found to consist of a modulated structure with . The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P63 structure with a large structural fluctuation and a monoclinic P21 phase with the single-q modulated structure.
6 citations
TL;DR: In this paper, structural phase transition and changes of microstrucrtures in BaAl2O4 with the tridymite tetrahedral framework structure were investigated by transmission electron microscopy experiments in the temperature range between 100k and 298k.
Abstract: We have investigated structural phase transition and changes of microstrucrtures in BaAl2O4 with the tridymite tetrahedral framework structure by transmission electron microscopy experiments in the temperature range between 100 K and 298 K. In our polycrystalline samples the transition from the paraelectric phase with the P6322 space group to the ferroelectric (FE) phase took place around 250 K, which accompanies with the appearance of the modulated structure with the three equivalent modulation wave vectors, q = 1/2 . Real-space images revealed that the FE phase should consist of nanodomains with the 10 ∼ 20 nm size. In addition, it is revealed that partial substitution of Fe3+ for Al3+ in BaAl2O4 induced structural phase transition to the modulated structure with q = 1/3 around x ∼ 0.50 in Ba(Al1-xFex)2O4.
6 citations
TL;DR: In this paper, the magnetic properties of multiferroic YbFe2O4 were investigated in the presence of an electrical current and the authors reported that the magnetization measured after cooling is ∼10-20% smaller than that after cooling without a current.
Abstract: We report the change in the magnetic properties of multiferroic YbFe2O4 caused by cooling in the presence of an electrical current. The magnetization measured after the cooling is ∼10–20% smaller than that after cooling without a current. The current also affects the magnetic anisotropy below ∼100 K; the magnetic coercivity is increased by ∼10–20%. These phenomena may arise from the coexistence of ferromagnetic and antiferromagnetic domains or a disturbance in the formation of charge-ordered domains. From the viewpoint of application, the enhancement of anisotropy by an electrical current provides a method for stabilizing magnetization other than the well-known method of exchange bias.
4 citations
3 citations
TL;DR: In this paper, the microstructures of the phases formed during diffusion bonding were investigated using transmission electron microscopy (TEM) and selected-area diffraction analysis, and the effect of interlayer material and the direction of the SiC fibers in the substrate with respect to the interlayer was evaluated.
Abstract: Diffusion bonding was used to join silicon carbide (SiC) to SiC substrates using three kinds of interlayers: physical-vapor-deposited (PVD) Ti coatings (10 and 20 μm) on the substrate, Ti foils (10 and 20 μm), and a Mo–B foil (25 μm). Two types of substrates were used: chemical-vapor-deposited SiC and SiC fiber bonded ceramic (SA-TyrannohexTM), the latter having a microstructure consisting of SiC fibers and a carbon layer. The microstructures of the phases formed during diffusion bonding were investigated using transmission electron microscopy (TEM) and selected-area diffraction analysis. TEM samples were prepared using a focused ion beam, which allowed samples to be taken from the reacted area. The effect of the interlayer material and the direction of the SiC fibers in the substrate with respect to the interlayer was evaluated. Scanning electron microscopy and TEM revealed good diffusion bonds in all samples; however, some samples exhibited small amounts of microcracking. The diffusion bonded CVD SiC sample using the 10-μm-thick PVD-Ti interlayer formed more of the stable phase and less of the intermediate phases than the sample using the Ti foil. This behavior was caused by the presence of columnar Ti grains in the interlayer, which may have enhanced the migration of Si and C atoms in the interlayer. In the SA-Tyrannohex samples using the Ti-foil interlayer, the chemical reaction proceeded more rapidly when the fibers were parallel to the interlayer than when they were perpendicular. This behavior was likely caused by the hexagonal carbon layer always facing the Ti interlayer in the sample with perpendicular fibers; this peculiar microstructure reduced the mobility of Si and C migrating into the interlayer. The SA-Tyrannohex sample using the Mo–B foil as the interlayer had excellent diffusion bonds with no microcracks or voids. In this system, Mo5Si3C, Mo2C, and Mo5Si3 formed. While phases have anisotropic coefficient of thermal expansion (CTE), the CTE mismatch between those phases and the substrate was apparently smaller than the mismatch in the samples using Ti interlayers.
2 citations
Journal Article•
1 citations