Minoru Nakamizo

Raman spectra of ground natural graphite

Abstract Structural changes in Ceylon natural graphite with grinding were studied by Raman spectroscopy along with X-ray diffraction. The natural graphite shows a single Raman band at 1580 cm−1, but the ground graphite samples exhibit two Raman bands at 1360 and 1620 cm−1 in addition to the 1580 cm−1 graphite band. The 1360 cm−1 band increases in intensity with increasing grinding time, and becomes much stronger than the 1580 cm−1 band after 200-hr grinding. Raman results are compared with structural parameters such as effective Debye parameter and C0 spacing obtained from X-ray diffraction measurements, and discussed in terms of structural defects introduced into the crystal lattice of natural graphite. A linear relationship was obtained for the ground graphite when the relative intensity of the 1360 cm−1 band is plotted as a function of effective Debye parameter. The slope of the linear plot is different for the ground graphite from that for the graphitized cokes, indicating a difference in the type of structural defects involved.

Studies on X-ray diffraction and Raman spectra of B-doped natural graphite

Abstract The structure of B-doped natural graphite has been investigated using X-ray diffraction and Raman scattering methods. The B-doped graphite has crystal lattice parameters different from those of pristine graphite. The a-axis is elongated and the c-axis contracted by B doping. Furthermore, B doping induces both an increase in intensity of the 1360 cm−1 Raman band and the appearance of a new Raman band at 1620 cm−1, accompanied by a gradual shift of the 1580 cm−1 Raman band to a higher frequency. It appeared that boron doping introduces a local distortion around substitutional B atoms within the graphite layer planes.

Raman spectra of iron-containing glassy carbons

Abstract Iron-containing glassy carbons were prepared from carbonization of the copolymers of furfuryl alcohol with one of the ferrocene derivatives. Their structural changes with heat treatment were studied with X-ray diffraction and laser Raman spectroscopy. Addition of iron to glassy carbons decreases both the half band width and intensity of a defect-induced Raman band at 1360 cm −1 at temperatures as low as 700°C and accelerates carbonization and graphitization of carbon precursors.

Raman spectra, effective Debye parameter and magnetoresistance of graphitized cokes

Abstract The Raman intensity ratio R ( I 1360 I 1580 ), the effective Debye parameter Beff and the maximum transverse magnetoresistance ( Δρ ρ ) mx at liquid nitrogen temperature and 10 kG were measured on various cokes heat-treated at high temperatures. The observed values of R, Beff and ( Δρ ρ ) mx are closely related with each other and are discussed in relation to the lattice defects in the graphite layer planes. The plot of R against Beff shows a linear relation, suggesting that both parameters are related to projections along a- and c-axes respectively of the same carbon atom displacement due to lattice defects. With decreasing Beff, ( Δρ ρ ) mx increases gradually but almost linearly with Beff and then rapidly. This behavior has been interpreted by an analysis based on a simple two band model.

Liquid Crystalline Compounds Exhibiting Two Smectic B Modifications

Abstract Four liquid crystalline compounds, i.e., three terephthal-bis-4-n-alkylanilines (TBAA; alkyl = pentyl, hexyl, and heptyl) and N-(4-n-heptyloxybenzylidene)-4-n-hexylaniline (HBHA) were synthesized and the phase transitions were studied by means of optical microscope, differential scanning calorimeter and miscibility relationships. It is indicated that all the compounds exhibit a smectic B-smectic B phase transition of which the transition heat is very small. Furthermore, a brief description is given of a smectic phase of TBAA which occurs only monotropically.

Formation of carbonaceous mesophase at lower temperature

Abstract The effects of heat-treatment at lower temperature on the formation of carbonaceous mesophase were studied. Heat-treatments of QS pitch below 340°C and of KF asphalt below 370°C lead to the formation of mesophase spherules having a different structure from those found previously. For QS pitch, the lowest temperature of mesophase formation was 290°C but more than one month was required for heat-treatment. The structure of the fourth-type spherule is proposed from the microscopic observations and its orientational behavior in a magnetic field. The structure of this type is very similar to that of the Brooks-Taylor-type one, and it is believed that the fourth-type spherule is a meta-stable phase of the Brooks-Taylor-type one.

On the phosphorescence rise and decay processes of phenanthrene in EPA at 77°K

Abstract Phosphorescence rise and decay behaviors of phenanthrene have been studied in EPA at 77°K. The rise curves follow exactly an exponential law, and the rate constants obtained from the curves are always larger than or equal to the phosphorescence decay constant, depending on excitation intensity and wavelength. Fluorescence rise curves have been also studied in the same system and found to be time-dependent at t > 0.2 sec after the excitation onset. The results obtained are interpreted in terms of a kinetic model involving a process of the depletion of ground-state molecules caused by excitation to their higher electronic levels, with subsequent population in the lowest excited singlet and triplet states.

Thermal conductivities and Raman spectra of boron-doped carbon materials

Abstract Boron-doped carbons were prepared at temperatures from 1000 to 2800°C. The effect of boron doping on the thermal conductivity of carbons has been studied and discussed with the results from Raman scattering. Boron doping above 2200°C depressed the thermal conductivity of carbons and increased the intensity of the 1360-cm −1 Raman band. It appeared that lowering the thermal conductivity is mainly caused by a distortion of the graphite lattice due to boron doping.

Spectroscopic study of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)2-hydroxybenzylidene]hydroxyanilines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]hydroxyanilines were synthesized. All 4-hydroxyaniline derivatives exhibited a nematic phase, while 3-hydroxyaniline and 2-hydroxyaniline derivatives exhibited only a nematic phase as the terminal alkoxy group was lengthened. Infrared spectra suggest that the 4-hydroxyaniline derivatives form intermolecular hydrogen bonding of the single bridge type, while the 3-hydroxy and 2-hydroxy derivatives form the polymer type. The Raman band at around 1360 cm-1 exhibited large differences in intensity among these derivatives. This can be explained by the effect of intermolecular or hydrogen bonding molecular conformation.

Electro-optic effects in smectic C liquid crystals

Abstract Electro-optic effects are observed in the smectic C states of 4- n -heptyloxybenzoic acid, 4- n -octyloxybenzoic acid. 4,4′-bis- n -heptyloxyazoxybenzene, and 4- n -decyloxy cinnamic acid under the application of an external ac electric field. The stripe domain pattern is observed for all the compounds studied above the first threshold. In the smectic C state there exists a second threshold at which the direction of the domain lines changes.