Microstructure and thermoelectric properties of Y x Al y B14 samples fabricated through the spark plasma sintering

Abstract

Excellent control in p-and n-type transport characteristics was previously obtained for the thermoelectric Y x Al y B 14 compounds through Al flux method. In this study, new attempts were made to reduce their grain sizes to obtain dense samples and to possibly lower the thermal conductivity. Introducing the reduction of grain sizes into Y x Al y B 14 samples was attempted by two methods; one was through mechanical grinding, and the other was by synthesizing Y x Al y B 14 via Y 0.56 B 14 (denoted as ''vYB-YAlB 14 ''). Mechanical grinding using ball milling with Si 3 N 4 pots and balls was found not to be an efficient way to decrease the grain size because of contamination of Si 3 N 4 . In contrast, vYB-YAlB 14 samples were successfully synthesized. Through the synthesis of Y 0.56 B 14 , the boron network structure was first formed. Afterward, Y x Al y B 14 was obtained by adding Al in the boron network structure through a heat treatment. Due to shorter heating time at lower temperature, the grain sizes were discovered to be smaller than that of Al flux method. The decrease of grain size was found to be beneficial for the densification of Y x Al y B 14 and the decrease of its thermal conductivity.

Zr doped β-rhombohedral boron: Widely variable Seebeck coefficient and structural properties

“…From a practical point of view, the huge variation in the Seebeck coefficientvalues from positive to negative we find in Zr-doped β-rh B is quite striking. With the rare ntype behavior reaching values of -600 VK -1 , it is significantly larger than the -200 VK-1 observed in YAlB 14 with varying Al occupancy which has recently gained sizable attention[54][55][56][57].…”

Thermoelectric properties of boron carbide/HfB2 composites

“…However, previous results in borides indicate that the penalty from reduction in electrical conductivity with porosity typically largely outweighs the benefit in reduction in thermal conductivity [30,32,39]. As a result, there have been many efforts to densify thermoelectric borides [30,32,39,40,52]. Therefore, the fact that in relatively dense samples, the doping of HfB 2 results in an overall reduction in the thermal conductivity, in contrast to the increase in electrical conductivity, indicates the potential of HfB 2 as an enhancer of thermoelectric properties.…”

“…We cannot simply estimate the effect of porosity on the electrical conductivity. However, previous results in borides indicate that the penalty from reduction in electrical conductivity with porosity typically largely outweighs the benefit in reduction in thermal conductivity [30,32,39]. As a result, there have been many efforts to densify thermoelectric borides [30,32,39,40,52].…”

“…These features are inherently desirable for thermoelectric energy generation, and particularly so for high-temperature applications. Wellknown boron compounds like boron carbide [17,[26][27][28] have been investigated for thermoelectrics, with recent striking p, n control demonstrated in Zr-doped b-boron [29], YAl x B 14 [30][31][32] and later also MgAlB 14 [33,34]. A renewed interest in RB 66 [22,35] has also arisen with large enhancements in ZT discovered for YB 48 [36] and SmB 66 [37].…”

Enhanced mechanism of thermoelectric performance of Bi2Se3 using density functional theory

“…Thermoelectricity has become fascinating prospect for use in generating green energy especially from the processes of waste heat [1][2][3]. The narrow-band gap (0.3 eV) semiconductor such as Bi 2 Se 3 has been recognized as an outstanding thermoelectric material [4][5][6].…”