Off-Center Guest Vibrations and Their Effect on Lattice Thermal Conductivity in n- and p-Type β-Ba8Ga16Sn30

• Published in: Journal of electronic materials 2009-07, Vol.38 (7), p.1516-1520
• Main Authors: Suekuni, Koichiro, Tanaka, Tomoo, Yamamoto, Shuhei, Avila, Marcos A., Umeo, Kazunori, Takasu, Yuichi, Hasegawa, Takumi, Ogita, Norio, Udagawa, Masayuki, Takabatake, Toshiro
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Condensed matter: structure, mechanical and thermal properties; Electronics and Microelectronics; Exact sciences and technology; Instrumentation; Lattice dynamics; Materials Science; Optical and Electronic Materials; Phonons and vibrations in crystal lattices; Physics; Solid State Physics
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-009-0686-6

We report on thermoelectric and Raman scattering studies of single crystalline samples of a type I clathrate Ba 8 Ga 16 Sn 30 . The n - and p -type samples have a thermopower of −300  μ V/K and +270  μ V/K, and electrical resistivity of 20 mΩ cm and 40 mΩ cm at room temperature, respectively. Regardless of the charge carrier type, the lattice thermal conductivity κ L shows typical glass-like behavior. The low-energy vibration of Ba(2) in the tetrakaidecahedron is manifested in the Raman scattering spectrum as a peak at 15 cm −1 . This energy agrees with the characteristic vibrational temperature of 20 K derived from the analysis of the specific heat data with a soft-potential model. The fact that both the vibrational energy and the magnitude of κ L for Ba 8 Ga 16 Sn 30 are lowest among the type I clathrates is evidence that off-center vibrations are responsible for the strong reduction of κ L . Analysis of κ L ( T ) revealed that the positional disorder associated with the off-center vibrations acts as the Rayleigh scattering center, and the coupling between guest vibrational modes and acoustic phonons is stronger than that in Sr 8 Ga 16 Ge 30 and Eu 8 Ga 16 Ge 30 .