2013/09/18 by Ken‐ichi Iwamoto, Tatsuya Mori, Iwamoto, K. +15 · 1 citation
Engineering · Materials Science · #Acoustic Wave Resonator Technologies #Advanced Thermoelectric Materials and Devices #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Solid-state spectroscopy and crystallography
paper · pdf · doi:10.48550/arxiv.1309.4524
openalex publication_date 2013/09/18 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We have investigated optical conductivity spectra of n- and p-type Ba8Ga 16Sn30 (α-BGS) with type-VIII clathrate structure, at temperatures from 296 K down to 6 K with a terahertz time-domain spectrometer (0.2 - 2.5 THz). The continuous spectra contributed from charge carriers are dispersive in this frequency range and also temperature- and carrier type-dependent. The Drude-Smith model taking multiple-scatterings of charge carriers into account well reproduces those data. The relaxation rate of the n-type carriers decreases more sharply than that in the p-type material, suggesting that a stronger electron-phonon interaction may exist in the n-type than in the p-type. On the other hand, the localized infrared-active modes observed at 1.3 THz and 1.7 THz, identified as the rattling phonons of the Ba2+ ion's quasi-on-center vibrations, become soft and broad significantly with decreasing temperature as well as observed in type-I BGS and BGG (Ba8Ga16Ge30) clathrates. The softening in the n-type is smaller by about 30% than in the p-type, whereas the linewidth brodening is almost the same independently on the carrier type. The difference in the softening is discussed with a scenario where the interaction of rattling phonons with carriers can modify the anharmonic potential of the guest ions. The anomalous broadening at low temepratures is also discussed by the impurity-scattering model presented for a rattling-phonon system strongly hybridized with acoustic cage phonons.