Hisashi Oshima

Annealing study of electron transport in slightly neutron-irradiated graphite.

A study has been made on the recovery of transport properties of synthetic single-crystal graphite irradiated with fast neutrons to a total dose of 3×1036nvt. Isochronal annealing was conducted stepwise between 100°C and 1600°C. An analysis based on the rigid two-band model gives a consistent account of the diffusion thermoelectricity and the galvanomagnetic effect. In addition to the major normal recovery between 200°C and 300°C, a reverse recovery in the carrier constitution is found to take place in the annealing range from 300°C to 350°C. This seems explicable by considering that divacancies are intermediately transformed to single vacancies during their annihilation process. The phonon-drag thermoelectric power vs. acceptor concentration relationship implies that positive holes are more strongly scattered than electrons by radiation-induced vacancies negatively charged by accepting electrons within the basal plane.

Electrical Conduction in C-Direction of Highly Crystalline Graphites in Relation to Structural Perfection

Electrical resistivity in c-direction (ρ c ) as a function of temperature ( T ) has been investigated of a number of highly crystalline specimens of kish and pyrolytic graphites in relation to their structural perfection evaluated by the basal-plane resistivity ratio between 300 K and 4.2 K ( R T =ρ a (300)/ρ a (4.2)). The ρ c vs R T plot indicates a \(\varLambda\)-shaped curve, and the ρ c vs T relationship becomes gradually metallic-like as R T increases. For pyrolytic graphite, the thinner the specimen the higher the perfection in the range 0.016 to 0.73 mm. Based on these observations, the intrinsic c -axis conduction is concluded to be described within the framework of band theory, while it is impeded by laminar defects and short-circuited sometimes by misaligned basal-planes especially in the pyrolytic specimens. Comparison is made with the theory of Ono who has taken into account the scattering of carriers by stacking faults.

Hall Effect in Graphite and Its Relation to the Trigonal Warping of Energy Bands. I. Experimental

The Hall effect study of graphite at low magnetic fields below 1.2 kOe has been extended over the four kinds of well-defined specimens and the low temperature range down to 4.2 K. Behaviors of the Hall coefficient are qualitatively accounted for in connection with the structural perfection of specimens by considering the resonance condition of the cyclotron motion of various carriers. The zero-field coefficient of the best-grade specimen exhibits a temperature dependence nearly in agreement with the band-theoretical calculation taking into account the trigonally warped Fermi surfaces in Slonczewski-Weiss-McClures model, while those of somewhat less perfect ones are reproduced by ignoring the warping. The contribution of mobile minority holes and the warping effect are concluded to be superimposed with each other.

c-Axis thermoelectric power of graphite intercalation compounds

Abstract c-Axis thermoelectric power (Sc) of ICl-GICs exhibits a gradual slope change around 80–100 K, though below the range Sc is proportional to T. A calculation based on the c-axis conduction theory developed by us, leads to a good agreement with our observed result for a stage-2 compound and it provides useful information on the scattering processes in the basal plane. The present work is an extension of our previous paper on a stage-1 compound.

Thermoelectric Power of Graphite Intercalation Compounds with Iodine Monochrolide

Thermoelectric power (TEP) of iodine monochrolide-graphite intercalation compounds (ICl–GICs) exhibits a linear temperature dependence at low temperatures, which is ascribed to the diffusion term. Above 200 K TEP levels off. This behavior stems from the phonon drag effect. By choosing an appropriate parameter set Sugiharas theory can provide a good fit with the observed TEP results for the stage-1 and -2 ICl–GICs.

Hall Effect in Graphite and Its Relation to the Trigonal Warping of the Energy Bands. II. Theoretical

Low field Hall coefficient R in well-crystalline graphite is positive at low temperatures. R reveals a maximum around 0.2 kOe at low temperatures and decreases rapidly with H →0. This trend can not be eplained without invoking the trigonal warping of the bands. The trigonal warping appreciably modifies the electron bands, and the harmonics induced by the trigonal warping corresponds to the appearance of the small effective mass carriers. This effect predominates over the contribution due to the holes around H -point. An exact calculation of R ( H →0) is carried out for γ 3 =0.29 eV, and the comparison with our measurements (I. Experimental) is performed.

Fabrication and Characterization of Nd-Substituted Bi4Ti3O12 Thin Films with

a- and b-axis-oriented (Bi4-xNdx)Ti3O12 (BNT; x = 0.5–1.0) films with 0.3 and 3.0 µm thicknesses, respectively, were fabricated on conductive IrO2(101)/Al2O3(012) substrates at 650 °C by high-temperature sputtering. The BNT films on the IrO2 electrode were preferentially a- and b-axis-oriented. The 3.0-µm BNT samples with x = 0.75–1.0 maintained a stable leakage current density range of 2.8 ×10-10–6.5 ×10-8 A/cm2 in the wide field range of 25–160 kV/cm. The remanent polarization (Pr) exhibited maxima (0.3 µm; 2Pr = 36 µC/cm2, 3.0 µm; 2Pr = 53 µC/cm2) at x = 0.75, regardless of film thickness. It is shown that the samples with x = 0.75–1.0 have relatively superior fatigue endurance due to a firm Bi/Nd–O bonding state formed with increasing Nd substitution.

a

Copper chloride intercalated pitch-based carbon fibers are found to have electrical resistivities as low as 12.9 micro-ohm-cm, and are air, and thermally stable at and above room temperature. This is therefore a good candidate system for conductor application. In addition, we find Shubnikov-deHaas quantum oscillatory effects, and electronic properties of the intercalated fiber are studied using magnetic fields to 20 tesla.

- and

Thermoelectric and thermomagnetic properties have been investigated of a single crystal graphite irradiated with fast neutrons of a total dose of 3×10 16 nvt, and after subsequently annealed at 250°C and 1400°C. The Seebeck coefficients ( S ) of the post-irradiated as well as the 250°C-annealed crystals are wholly positive at temperatures ( T ) between 300 K and 4.2 K, while the characteristic phonon drag anomaly still survives in the S vs T diagram, consisting of positive and negative components located around 25 K and 40 K respectively. Annealing at 1400°C, whereby the radiation-induced vacancies have mostly been recovered, makes the S vs T curve not much different from that of the unirradiated graphite, except for the doublet structure of the phonon drag dip. The presence of a magnetic field enhances the thermoelectricity in positive and/or negative direction. The Nernst-Ettingshausen coefficient measured at 6 kOe is also accompanied by the phonon drag anomaly having the doublet structure.

b

Abstract The nonsynchronous coil planet centrifuge has a unique mode of planetary motion in that it allows a freely adjustable rotational rate of the coiled separation column at a given revolution speed. This paper describes a series of studies using the apparatus fabricated in our laboratory on the countercurrent chromatographic separation of proteins with aqueous‐aqueous polymer phase systems, experimental and theoretical analysis of the effect of planetary motion on protein separation, and application to elutriation of cells such as blood cell components and mast cells using a single‐phase physiological buffer solution.