Hideo Iwasaki

Preparation and Chemical Composition of Superconducting Oxide Tl2Ba2Can-1CunO2n+4 with n=1, 2 and 3

Superconducting oxides of Tl2Ba2Can-1CunO2n+4 with n=1, 2 and 3 were synthesized, and their structure and chemical composition were examined by X-ray powder diffraction, EPMA, Rietveld analysis and electron microscopy. Partial substitution of Tl with Ca was confirmed, but the production of holes in Cu layers expected from this substitution was rather small for a 120 K superconductor. Charge transfer of Tl3-δ-Cu2+δ would provide both the hole in the Cu-O bond required for high Tc and s-like electron of Tl atoms for stabilization of layered structures.

Formation of Bismuth Strontium Calcium Copper Oxide Superconducting Films by Chemical Vapor Deposition

Superconducting films of bismuth strontium calcium copper oxides were prepared by chemical vapor deposition at 910?C and 1 Torr on MgO substrate using a bismuth alkoxide and ?-diketonate chelates of Sr, Ca and Cu as source materials. In the film with Tc(zero) of 78 K, the predominant phase was Bi2(Sr, Ca)3Cu2Ox with the c-axis perpendicular to the substrate.

Tc of c-Axis-Oriented Y-Ba-Cu-O Films Prepared by CVD

YBa2Cu3O7-x thin films (0.8 µm in thickness) with c-axis orientation were prepared at 900°C on yttria-stabilized zirconia substrates by chemical vapor deposition using metal chelates as source materials. The onset and completion of the superconductive transition occurred at 89 K and 80 K, respectively, for the film that received in situ oxygen treatment. The oxygen-treated film had metallic resistivity and the resistance ratio (R273 K / R100 K) was 2.

Evaluation of the Figure of Merit on Thermoelectric Materials by Harman Method

The figure of merit ZT of thermoelectric materials has been evaluated by the Harman method in the temperature region below room temperature. In this method only resistance measurements by both dc and ac methods are required to obtain the ZT values. ZT is given by ZT=(Rdc/Rac-1)/x, where Rdc, Rac and x are the resistance value by the ac and dc methods and the rate of the heat to the heat bath, respectively. The heat effect is experimentally confirmed to be negligibly small and we can use x=1 which corresponds to a sufficient adiabatic condition. Because an ambiguity due to experimental errors such as the length between the measurement terminals in the resistivity and the thermal conductivity measurements is removed, ZT can be determined very simply and precisely by the Harman method.

Historical review of quartz crystal growth

Abstract The history of quartz crystal growth is reviewed from the origin to the industrialization. The developing process of growth techniques is divided into the following three stages: (1) The fundamental work based on the mineralogical genetic view point, which was performed in Italy during the end of the 19th to the beginning of the 20th centuries. (2) The works to attempt the industrial application made in Germany and in England during World War II. (3) The industrialization of quartz growth after World War II. These were initiated in England, in USA and independently in Russia. The highest mass production process was developed in Japan. The historical flow is traced by the interview of several persons based on the original references.

The effect of Eu substitution on thermoelectric properties of SrTi0.8Nb0.2O3

Herein we demonstrate that Eu2+ substitution of SrTi0.8Nb0.2O3 is effective in reducing the thermal conductivity, with no reduction in the thermoelectric power factor (S2σ; S, Seebeck coefficient; σ, electrical conductivity). We prepared cubic (Sr,Eu)Ti0.8Nb0.2O3 crystals having the same lattice parameter (a=0.395 nm) over the whole composition range. Although no dependence upon the Eu content was observed for the electron transport properties, including the density of states effective mass and carrier relaxation time for (Sr,Eu)Ti0.8Nb0.2O3, the mean free path of the phonon was reduced ∼12% at room temperature when half of the Sr2+ was substituted by Eu2+.

Impurity Species in Synthetic and Brazilian Natural Quartz

Impurity species in synthetic and Brazilian natural quartz were studied by means of infrared absorption spectroscopy and atomic absorption spectrometry. It is shown that almost all of the Al ions in synthetic quartz are incorporated as a substitutional type of Al(3+). The possibility of the existence of interstitial Al is small. In the formation of Al-related centers in crystals grown in Li-containing solution, the dominant charge compensator for Al(3+) is Li(+). In natural quartz, the charge of Al(3+) is compensated by Li(+) and H(+) to form Al-Li and Al-OH centers. Na(+) ions are incorporated into crystal with H2O impurities both in synthetic and natural quartz. The content of Al-hole centers due to ? irradiation is approximately proportional to the content of Al-Li centers and inversely proportional to H2O impurity content.

Preparation of Bi-Sr-Ca-Cu-O Superconducting Films by CVD

Bi-Sr-Ca-Cu-O (BSCCO) films were prepared on MgO(100) single-crystal substrates at 770°C by chemical vapor deposition using β-diketone metal chelates of Sr, Ca and Cu and Bi-triethoxide. The films were Bi2(Sr, Ca)3Cu2Ox (c=30 A) with c-axis orientation. The films showed superconducting transition onset at 90 K with zero resistivity at 74 K. The formation of films having high-Tc phase (Bi2(Sr, Ca)4Cu3Ox, c=37 A) was achieved when the films were annealed at 890°C for 5 h under 760 Torr of oxygen. The resistivity of the annealed films began to drop sharply at around 110 K and reached zero at 77 K.

Evaluation of Thermoelectric Properties in Bi-Microwires by the Harman Method

We have improved the Harman method to evaluate all thermoelectric properties related to the figure of merit, ZT, not only in bulk materials but also in mesoscopic ones. By this method, the ZT of single microwires can also be determined. The minimum sample size is currently ~0.25 mm in length and ~10 µm in diameter. The fabrication of our equipment based on the Harman method is described in detail. The enhancement of ZT can be achieved in the Bi-microwire array because of the homogeneous arrangement of the crystal orientation in each microwire. The results obtained in the Bi-microwire arrays are consistent with ZT behavior in the single microwires extracted from the arrays.

Impurity content characterization of brazilian quartz lascas

Lattice impurities (Al, Li, Fe) free from the influence of cations in inclusion liquid were evaluated by atomic absorption spectrophotometry (AAS) in quartz lascas taken from 10 deposits with known localities in three states, Minas Gerais, Tocantins and Bahia. Levels of Al content and associated Li content depend on the localities of deposits. Quartz deposit regions with high Al content are composed of granite, gneiss, and pegmatite as surrounding rocks. It was concluded that the charge compensation for Al-Si substitution in quartz lascas was realized substantially by the formation of Al-Li and Al-OH centers which were confirmed from the linear relation of Al-Li plots by AAS data and IR spectra due to Al-OH center. The variety in Al-Li and Al-OH correlations was attributed to the fluctuation of growing conditions of quartz in nature.