Thermoelectric properties of sintered clathrate compounds Sr8GaxGe46−x with various carrier concentrations

Abstract

Polycrystalline samples of Sr8GaxGe46−x clathrates with varied nominal Ga contents were prepared by powder metallurgy to produce n-type samples with carrier concentration n of 1.8×1020–1.1×1021cm−3. Their thermoelectric properties were measured in the temperature range from 300to900K. Their Seebeck coefficient and electrical conductivity were found to be typical for a heavily doped semiconductor, and varied systematically with their carrier concentration. The maximum value of the figure-of-merit ZT was 0.62 at 800K for n=5.6×1020cm−3. Other following properties were also measured or estimated, and their relationships with the thermoelectric properties are discussed. The band gap of the samples was estimated to be 0.4–0.5eV; their effective mass was an almost constant value of 3.1me at room temperature, and this value decreases with increasing temperature; and their electron Hall mobilities were 8–13cm2V−1s−1 at room temperature, increasing slightly with decreasing carrier concentration.

Thermal stability and thermoelectric properties of p-type Ba8Ga16Ge30 clathrates

“…The BGG4a sample exhibits a slight increase in charge carrier concentration with temperature, while for BGG4b no trend could be discerned due to large scattering of the data above room temperature. The room temperature charge carrier density for samples BGG1-BGG4a agrees well with what is found in literature, 29,40 while the result for BGG4b is somewhat lower than previously reported for the Ba 8 Ga 16 Ge 30 system.…”

Growth and thermoelectric properties of Ba8Ga16Ge30 clathrate crystals

“…It has been reported that the thermoelectric properties of type I clathrate vary in a wide range with the stoichiometric composition and homogeneity. For example, the maximum ZT value of Ba 8 Ga 16 Ge 30 synthesized by Martin et al was reported as 0.8 at 850 K [7], while a similar material prepared by Fujita et al only owned maximum ZT of 0.62 at 800 K [3]. Synthesizing homogeneous and reproducible clathrate material with high ZT values is still a challenge.…”

“…Since then an increasing number of papers treating the thermoelectric properties of type I clathrates have been published, such as Sr 8 Ga X Ge 46−X , Ba 8 Ga 16 Ge 30 and Eu 8 Ga 16 Ge 30 [3][4][5][6]. It has been reported that the thermoelectric properties of type I clathrate vary in a wide range with the stoichiometric composition and homogeneity.…”

Optimization of thermoelectric properties of type-VIII clathrate Ba8Ga16Sn30 by carrier tuning

“…The optimally doped n-type sample with x = 0.25 has the maximum ZT = 0.86 at 950 K [9,10]. Similarly, Ba 8 Ga 16 Si 30 and Sr 8 Ga 16 Ge 30 exhibit ZT values 0.9 at 870 K and 0.6 at 800 K, respectively [11,12]. These compounds were regarded as examples those fulfill the phonon glass and electron crystal concept proposed by Slack [13].…”