Single-crystalline Ba8Al x Ga y Si 46-x-y clathrates were synthesized by the arc melting method and Czochralski method without subsequent treatment, and their thermoelectric properties were compared with those of Ba8Al x Ga y Si46-x-y and Ba8Al x Si 46-x clathrates with almost the same carrier concentration as estimated from the similar Seebeck coefficient and the Zintl concept. The resistivity of Ba7.8Al5.3Ga7.4Si33.3 was lower than that of Ba7.9Al12.6Si33.4. The specific electrical resistance of Ba7.9Al12.6Si 33.4 and Ba7.8Al5.3Ga7.4Si 33.3 was 0.573 mΩ cm and 0.282 mΩ cm at 750 K, respectively. The band structure of Ba8Al8Ga 8Si30 and Ba8Al16Si30 was estimated by first-principle calculations using density functional theory with the local density approximation. Based on these calculations, it was found that the shape of the bottom of the conduction band for Ba8Al x Si46-x clathrate changed slightly on Ga doping and the radius of curvature of the bottom of the conduction band for Ba8Al 8Ga8Si30 clathrate was lower than that for Ba8Al16Si30 clathrate. These results indicate that the mobility was enhanced by Ga doping of Ba8Al x Si46-x clathrate. We also synthesized single-crystalline Ga-doped Ba8Al x Si46-x clathrate. The electrical resistivity decreased dramatically due to the single-crystallization because of reduced electron scattering on grain boundaries. These results suggest that Ga doping and single-crystallization are effective for improvement of the thermoelectric properties of Ba8Al x Si46-x clathrate.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering
- Materials Chemistry