2004 Fiscal Year Final Research Report Summary
Low temperature and High-pressure Raman Study of Superconductivity and Cage-structure Stability of Silicon Clathrates
| Project/Area Number |
15340095
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics I
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| Research Institution | Gifu University |
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Principal Investigator |
SHIMIZU Hiroyasu Gifu University, Faculty of Engineering, Professor, 工学部, 教授 (80023258)
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| Co-Investigator(Kenkyū-buntansha) |
SASAKI Shigeo Gifu University, Faculty of Engineering, Assoc.Professor, 工学部, 助教授 (30196159)
KUME Tetsuji Gifu University, Faculty of Engineering, Assistant, 工学部, 助手 (30293541)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Silicon Clathrates / High-pressure Raman Scattering / Superconductivity / Guest-Host Interactions / Cage Structures / Guest Vibration |
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| Research Abstract |
Silicon clathrates are covalent bonded cage-like crystals composed of face-sharing Si_<20>, Si_<24>, and Si_<28> polyhedra in which guest atoms are occupied. These compounds continue to attract much attention as new superconductors, unusual wide-bandgap semiconductor, and a new class of thermo-electric materials. Vibrational properties of guests and host lattice, and the guest-host interactions are studied by high-pressure Raman spectroscopy.
High-pressure Raman scattering of type-I silicon clathrates, Ba_8Si_<46>, K_8Si_<46>, and I_8Si_<44>I_2, and type-III Ba_<24>Si_<100> were measured up to about 30 GPa. Low-frequency vibrational modes associated with Ba, K, and I atoms isnside two or three kinds of cages were found around 40-110 cm^<-1>. The silicon framework Raman bands were also observed around 110-450 cm^<-1>. Pressure-induced phase transitions occurred at high pressures. They are closely related to the motions of guest atoms and the guest-host interactions. At higher pressures, the pressure-induced amorphized irreversible transitions were found, which were discussed by comparing the amorphous silicon at high pressures.
By considering these results and high-pressure phase transitions of Si clathrates, we investigate their characteristics depending on guests and cage-structures, and the stability of cage-structures.
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