Year: 2009
Type: article
Abstract: A series of infrared-active optical phonons have been detected in type-I clathrate ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Ge}}_{30}$ by terahertz time-domain spectroscopy. The conductivity spectra with the lowest-lying peaks at 1.15 and 1.80 THz are identified with the so-called rattling phonons, i.e., optical modes of the guest ion ${\text{Ba}}^{2+}(2)$ with ${T}_{1u}$ symmetry in the oversized tetrakaidecahedral cage. The temperature dependence of the spectra from these modes are totally consistent with calculations based on a one-dimensional anharmonic potential model that, with decreasing temperature, the shape becomes asymmetrically sharp associated with a softening for the weight to shift to lower frequency. These temperature dependences are determined, without any interaction effects, by the Bose factor for optical excitations of anharmonic phonons with the nonequally spaced energy levels.
Source: Physical Review B
Authors: T. Mori, S. Goshima, K. Iwamoto, S. Kushibiki, H. Matsumoto, N. Toyota, K. Suekuni, M. A. Avila, T. Takabatake, T. Hasegawa, N. Ogita, M. Udagawa
Institutions: Tohoku University, Hiroshima University
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1492765173