A systematic study on the anharmonicity of phonons is made for single-crystal type-I clathrates: n-type Ba8Ga16Ge30 (n-BGG), p-type Ba8Ga16Ge30 (p-BGG), n-type Sr8Ga16Ge30 (n-SGG), n-type K8Ga16Sn30 (n-KGSn), and n-type Ba8Ga16Sn30 (n-BGSn), based on their heat capacity Cp at low temperatures (T) down to 360 mK. The low-T linear terms obsI T of Cp, including the tunneling term of the atoms accommodated in the host cages (I phT=Î±T) and the Sommerfeld itinerant-electron term (I eT), are successfully separated through careful measurements of single crystals with various carrier concentrations. The values of the minimum density of anharmonic potentials are deduced from Î± to be 0.12±0.24 for n-KGSn, 0.47±0.24 for n-BGG, 1.9±0.8 for p-BGG, 6.0±0.9 for n-SGG, and 10.9±0.7 for n-BGSn in units of ×1015 cm 3. The effective mass (m*/m0) is determined from I to be 1.01±0.25 for n-BGG, 1.20±0.19 for p-BGG, 1.68±0.24 for n-SGG, 1.86±0.54 for n-KGSn, and 2.05±0.48 for n-BGSn in units of free electron mass m0, and the electron-phonon interaction strength can be evaluated from these values. It is shown that both the thermal conductivity and the electron-phonon interaction strength agree well with the Î± parameters deduced from Cp. The differences in known between n- and p-BGGs are ascribed to the influence of defects at the crystallographic 6c sites, which are clearly indicated by magnetic susceptibility measurements. This is very different from the situation in the other clathrates.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2014 Jun 3|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics