High thermoelectric performance of Cu substituted type-VIII clathrate Ba8Ga16–xCuxSn30 single crystals

Abstract

Single crystalline samples of type-VIII clathrate Ba 8 Ga 16-x Cu x Sn 30 (0 x 0.033) were prepared by the Sn-flux method. Upon substituting Cu for Ga, the carrier mobility at 300 K increases twice while the carrier density stays in the range 3:1 À 4:2 Â 10 19 =cm 3. Consequently, the electrical resistivity is decreased from 5.3 mXcm for x ¼ 0 to 3.2 mXcm for x ¼ 0.033. Irrespective of x, the Seebeck coefficient is largely negative and linearly changes with temperature in the range 300 < T < 600 K. The thermal conductivity is in the range 0:68 À 0:74 W/Km at 300 K for all samples. The dimensionless figure of merit ZT for x ¼ 0.033 reaches the maximum of 1.35 at 540 K.

Estimating Energy Conversion Efficiency of Thermoelectric Materials: Constant Property Versus Average Property Models

“…The one exception in Table I is Bi x Sb 2-x Te 3 , which has equivalent average and peak ZT due to the atypical feature of the maximum being located near the midpoint of the measured temperature range. Although considerable emphasis is placed on achieving high peak or maximum ZT in contemporary thermoelectric materials research literature, 12,13,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] it is not as important as achieving high average ZT. Furthermore, the need for high average ZT can place greater expectations on the corresponding requisite value of peak or maximum ZT.…”

Electronic Structures and Thermoelectric Properties of Sb-Doped Type-VIII Clathrate Ba₈Ga₁₆Sn₃₀

“…In particular, Al-and Cu-doped n-type BGS-VIII samples show high ZT values. 7,8) On the other hand, Sb-doped p-type BGS-VIII has high ZT value. 6,24) According to the Zintl concept for the clathrate, 25) electron carrier doping is realized by the partial substitution of Sb(5s 2 5p…”

“…The guest atoms (Ba) occupy 8c sites, whereas the host atoms (Ga and Sn) occupy 2a, 8c, 12d, and 24g sites. Sn-based clathrate Ba 8 Ga 16 Sn 30 also have a type-I crystal phase. Synthesis of each phase can be controlled by tuning the heat treatment in the growth processes, but the type-I phase is less stable than the type-VIII phase.…”

“…The crystal structure of type-VIII Ba 8 Ga 16 Sn 30 (BGS-VIII) is characterized by the space group I 43m; its unit cell is shown in Fig. 1.…”

“…This rattling mode effectively scatters thermal-conducting phonons and causes glass-like low thermal conductivity. Some researchers have reported this PGEC features lead to a high dimensionless figure of merit (ZT) in Ge clathrate compounds, with values of 1.35 (900 K, n-type Ba 8 Ga 16 Ge 30 ), 3) 1.25 (940 K, n-type Ba 24 Ga 15 Ge 85 ), 4) and 0.9 (680 K, p-type Ba 8 Au 5.3 Ge 40.7 ) 5) being observed. Recently, some authors also reported high ZT values in Sn-based clathrates with type-VIII structures.…”