IKAWA Atsushi Kyoto University Graduate School of Science Assistant Professor, 大学院・理学研究科, 助教授 (80243004)
HOSHINO Hideoki Hirosaki University Faculty of Education Professor, 教育学部, 教授 (30001861)
ENDO Hirohisa Fukui Institute of Technology Faculty of Engineering Professor, 工学部, 教授 (40025284)
HIROYUKI Ikemoto Toyama University Faculty of Science Assistant, 理学部, 助手 (20262496)
TATUKI Oda Kanazawa University Faculty of Science Lecturer, 理学部, 講師 (30272941)
|Budget Amount *help
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 2000: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1999: ¥2,400,000 (Direct Cost: ¥2,400,000)
(1) First-principles electronic structure calculations have been carried for all high-pressured phases (Se-I, II, III, IV, X, VI) of Selenium with using a full-potential augmented plane wave (FLAPW) method, based on the density functional theory (LDA and GGA calculation), and the pressure-inducced phase transitions have been discussed. Through the transiton, Se-I→Se-II, the trigonal chain in Se-I is folded on a plane. Lone-pair orbitals which exist on all atoms in Se-I vanish partially in Se-II and entirely in Se-III.The electronic structure in Se-III shows a complete metalic behavior. A new structure of Se-IV have been proposed, which could reasonably explain a second-order property of the phase transition between Se-IV and V.The proposed structure is consistent with the extinciton low of the X-ray diffraction measurement and the space group of Se-IV have been determined to be P2_1/m. The transition pressure between Se-V and VI has been estimated from the total energy calculation and
the agreement with experimental value are good.
(2) Classical molecular dynamics simulations on A2X2 (A=S, Se ; X=Cl, Br) are performed with the model based on the ab-initio molecular orbital calculations. The static and dynamic structure factors are compared with the experiments of neutron scattering. IR absorption spectrum on amorphous Se is calculated and analysed. We find the double peak structure in the stretching band is caused by the presence of an intermediate range order in the sequence of dihedral angles in Se chains.
(3) Magnetoresistance and Hall coefficients measurements have been carried out for liquid As-Te and Se-Te mixtures in order to investigate a mechanism of semiconductor to metal transition with covalent bonds. There are interesting features on plots of magnetoresistance and Hall coefficients against conductivities. While the magnetoresistance is not observed in the semiconductor region, positive magnetoresistances are observed in the semiconductor to metal transition region and the metallic region. Values of the magnetoresistance lie on a unique line irrespective of concentrations in As-Te and Se-Te mixtures. The values increase rapidly with increasing conductivity. The Hall coefficients of As-Te mixtures are nearly constant in the semiconductor region. Absolute values of the Hall coefficients bend downward around the so-called minimum metallic conductivity, and decrease to much smaller values. When the Hall coefficient data are extrapolated by linear functions, they converge on the same point. Less