High Thermoelectric Performance of Dually Doped ZnO Ceramics

Abstract

A marked improvement in the thermoelectric performance of dense ZnO ceramics is achieved by employing a third element as a co-dopant with Al. Dual doping of ZnO with Al and Ga results in a drastic decrease in the thermal conductivity of the oxide, while the decrease in the electrical conductivity is relatively small. With the aid of a significant enhancement in the thermopower, the dually doped oxide shows thermoelectric figure of merit values, ZT, values of 0.47 at 1000 K and 0.65 at 1247 K at the composition Zn 0.96 Al 0.02 Ga 0.02 O. These results appear to be the highest ZT values so far reported for bulk n-type oxides. Microscopic observation of the samples reveals a granular texture in the densely sintered oxide matrix, suggesting that considerable reduction of the thermal conductivity while maintaining high electrical conductivity could be achieved by such a bulk nanocomposite structure in the samples.

Metal oxides for thermoelectric power generation and beyond

“…Because the doped Al 3+ and Ga 3+ usually substitute for Zn 2+ in ZnO and act as n-type donors, these dopants significantly enhance the electrical property of ZnO. Furthermore, the largest PF value [93], which remains the highest PF of all high-temperature n-type oxides that was ever reported.…”

“…Despite the high Seebeck for the Al-doped nano-bulk and bulk ZnO samples, the electrical conductivity of these samples is extremely low leading to a small PF value. Compared to their nano-structured counterparts, the bulk Zn 0.96 Al 0.02 Ga 0.02 O and Zn 0.98 Al 0.02 O alloys showed a higher PF in the temperature range from 300 to~1300 K [92,93], which can be attributed to a better crystal quality in the bulk materials leading to higher electrical conductivity. Because the doped Al 3+ and Ga 3+ usually substitute for Zn 2+ in ZnO and act as n-type donors, these dopants significantly enhance the electrical property of ZnO.…”

Thermoelectric properties of n-type SrTiO3

“…The best n-type to date is found in ZnO ceramics at high temperatures. [15][16][17][18] Among the several n-type oxides, SrTiO 3 (STO) with cubic perovskite structure has attracted growing attention for TE power generation at high temperatures due to its large Seebeck coefficient originated from the degenerate Ti 3d-t 2g band at the conduction band minimum (CBM) and high power factor (PF) comparable to that of Bi-Te alloy. 19 However the ZT value achieved is still quite low (<0.5) even at 1000 K. This is mainly attributed to its high thermal conductivity (6-12 W m −1 K −1 for undoped STO 20 ).…”

Recent aspects of oxide thermoelectric materials for power generation from mid-to-high temperature heat source

“…The thermoelectric performance of the oxide was thereby markedly improved by the co-doping, obtaining ZT = 0.47 at 1000 K and ZT = 0.65 at 1273 K for Zn 0.96 Al 0.02 Ga 0.02 O 45 as shown in Fig. 6.…”