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Yamaguchi, Daisuke; Mayama, Hiroyuki*; Koizumi, Satoshi; Tsujii, Kaoru*; Hashimoto, Takeji
European Physical Journal B, 63(2), p.153 - 163, 2008/05
The fractal dimensions of specific porous silica materials were investigated by a wide-q observation using ultra-small-angle neutron scattering technique. In order to control the fractal dimension of porous silica material, flaky particles made of alkylletene dimer (AKD) were employed as moulds and silica matrix was formed by sol-gel process. After the solidification of the silica matrix, the original AKD moulds were completely burnt away at high temperature (ca. 930K) and became pores having a particular fractal dimension. The fractal dimension of the pores was changeable by the compression of the AKD mould at different ratio during the sample preparation. We found that the fractal structure obtained in this study was distinctly different from those of ordinary silica aerogels.
Yamaguchi, Daisuke; Mayama, Hiroyuki*; Koizumi, Satoshi; Tsujii, Kaoru*; Hashimoto, Takeji
European Physical Journal B, 63(2), p.153 - 163, 2008/05
Times Cited Count：12 Percentile：48.4(Physics, Condensed Matter)The unique structure of a set of self-assembled porous silica materials was characterized through a combined small-angle scattering (CSAS) method using small- and ultra-small angle neutron scattering as well as small-angle X-ray scattering. The porous silica specimens investigated were prepared by a sol-gel method under the presence of alkylketene dimer (AKD) template particles and through calcination, which leads to the development of porous silica having a mass-fractal structure over length scales from 10nm to 10
m. Furthermore, the specimens posses a hierarchical structure, which consist of a fractal porous structure, and also contain primary silica particles less than 10 nm in size, which form a continuous silica matrix. To characterize these complex structures, observation over a broad range of length scales is indispensable. We propose a CSAS technique that serves this purpose well.
= 1 antiferromagnet observed by specific heat measurementsHagiwara, Masayuki*; Tsujii, Hiroyuki*; Rotundu, C. R.*; Andraka, B.*; Takano, Yasumasa*; Tateiwa, Naoyuki; Kobayashi, Tatsuo*; Suzuki, Takafumi*; Suga, Seiichiro*
Physical Review Letters, 96(14), p.147203_1 - 147203_4, 2006/04
Times Cited Count：19 Percentile：67.26(Physics, Multidisciplinary)Specific-heat experiments on single crystals of the = 1 quasi-one-dimensional bond-alternating antiferromagnet Ni(C
H
N
)(NO
)(ClO) (NTENP) have been performed in magnetic fields applied both parallel and perpendicular to the spin chains. We have found for the parallel field configuration that the magnetic specific heat (
) is proportional to temperature (
) above a critical field 
, at which the energy gap vanishes, in a temperature region above that of the long-range ordered state. The ratio = increases as the magnetic field approaches from above. The data are in good quantitative agreement with the prediction of the 
=1 conformal field theory in conjunction with the velocity of the excitations calculated by a numerical diagonalization, providing conclusive evidence for a Tomonaga-Luttinger liquid.
Yamaguchi, Daisuke; Miyamoto, Nobuyoshi; Koizumi, Satoshi; Nakato, Teruyuki*; Mayama, Hiroyuki*; Tsujii, Kaoru*; Hashimoto, Takeji
no journal, ,
no abstracts in English
Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Koizumi, Satoshi; Hashimoto, Takeji; Nakato, Teruyuki*; Mayama, Hiroyuki*; Tsujii, Kaoru*
no journal, ,
The hierarchical structures composed of two-dimensional particles were observed via ultra-small-angle scattering method. We have investigated two systems: (1) exfoliated K
Nb
O
nanosheet colloidal dispersion, (2) porous silica fabricated from alkylketene dimer template. Although the physical and chemical structures and properties are largely different in these two systems, a similar point to them is regarded as below. The thickness of the constituent particles is ranging from a few nanometers to several tens of nanometers. Various fractal-like power-law scattering were obtained in the ultra-small angle scattering region reflecting the difference in the self-assembly of the particles.
Yamaguchi, Daisuke; Mayama, Hiroyuki*; Koizumi, Satoshi; Tsujii, Kaoru*; Hashimoto, Takeji
no journal, ,
The fractal dimensions of specific porous silica materials were investigated by ultra-small-angle neutron scattering (USANS). In order to control the fractal dimension of porous silica material, flaky particles made of alkylletene dimer (AKD) were employed as moulds and silica matrix was formed by sol-gel process. The fractal dimension of the pores was changeable by the compression of the AKD mould at different ratio (hereafter designated as r) before the mould was filled with a TMOS solution, which turned to silica matrix, and three specimens, of which r = 1, 2, and 3, were prepared. USANS measurements brought us wide-q observations of the specimens, in the q scale of more than three orders of magnitude, and made it possible to accurate evaluation of the fractal dimension. The resultant mass-fractal dimensions for the specimens of r = 1, 2, and 3 were 2.98, 2.74, and 2.67, respectively.
Yamaguchi, Daisuke; Mayama, Hiroyuki*; Koizumi, Satoshi; Tsujii, Kaoru*; Hashimoto, Takeji
no journal, ,
In this study, the structure of the "novel" porous silica specimens prepared by sol-gel method with alkylketene dimer (AKD) template was characterized on the length scale from nanometers to tens of microns by small-angle neutron scattering measurements. AKD is a kind of wax and has been proven to form a fractal structure by recrystallization. Due to the AKD template, the porous silica product exhibited a distinct mass-fractal structure, which persists over the length scale ten times larger than that of conventional silica aerogel. While on the other hand, the mass fractal dimension is similar between the silica aerogels and the specimen investigated in this study, suggesting that the space symmetry is somewhat similar between those two systems.
Kitazawa, Hideaki*; Kawamura, Yukihiko*; Mamiya, Hiroaki*; Terada, Noriki*; Suzuki, Hiroyuki*; Tsujii, Naohito*; Doenni, A.*; Kaneko, Koji; Metoki, Naoto; Igawa, Naoki; et al.
no journal, ,
In this paper, we will demonstrate some application of neutron scattering for magnetic refrigerant materials Ho
Pd and dilute spinel ferrites. In order to determine the magnetic structure, we have performed neutron powder diffraction experiments at JRR-3. The magnetic peaks with a propagation vector k = (0.18, 0.18, 0.18) are gradually developing. The peak width is significantly broader even 5 K, indicating a short-range order with a long wave length.
