Effects of Metal Doping on Thermoelectric Properties of Arc-Melted and Hot-Pressed β-Rhombohedral Boron

Abstract

Thermoelectric properties of metal (V, Co, Zr, Sr, W)-doped -rhombohedral boron (-Boron) were examined in the temperature range from 353 K to 1073 K. Doping with V (V 1:5 B 105 ), which preferentially occupy the A 1 sites, results in a great increase of electrical conductivity and a negative Seebeck coefficient S, while doping Co, Zr, Sr or W (M 1:0 B 105 , M ¼ Co, Zr, Sr or W) also increases the though S remains positive. By crushing and hot pressing as-melted samples, the thermal conductivity was decreased to almost half of that of arc-melted samples. As a result, V-doped and hot-pressed n-type -Boron had a ZT value of about 0.01 at 885 K, which approaches that of boron carbide, which exhibits the maximum ZT value among the boron-rich icosahedral cluster solids.

Theoretical and experimental investigation of the excellent p–n control in yttrium aluminoborides

“…However, TE modules require p-type and n-type materials with matching structure, and the lack of a suitable matching n-type counterpart for boron carbide has been a longstanding problem since icosahedral boron compounds have been found to be predominantly p-type. Slack first showed the n-type characteristics of vanadium-doped β -boron [11, 12], and extensive tests have been conducted for various dopants [13–15]. However, all such n-type borides undergo metallization, whereby the Seebeck coefficient decreases with increasing temperature, in contrast to the temperature dependence of boron carbide.…”

Vanadium Concentration Dependence of Thermoelectric Properties of β-Rhombohedral Boron Prepared by Spark Plasma Sintering

“…Nevertheless, the values of for these SPS samples are much lower than those for arc-melted bulk samples. 9) On the other hand, when x ! 1:5, increases with increasing V concentration owing to the formation of a second phase, VB 2 , which has a larger value of .…”

“…This is because a large increase in ' and a decrease in were possible owing to the metallic-covalent bonding conversion around the A 1 sites and to the decrease in grain size induced by SPS, respectively, although the value of S decreased and became negative. [9][10][11] As a result, V-doping is focused on in this paper. Table 1 shows the V concentration of three samples obtained by ICP analysis.…”

“…The occupancy of doping sites by foreign atoms has a great effect on the electrical and thermal properties of -boron. In previous studies, [9][10][11] the V, Co, Zr, Sr and W doping of -boron was attempted and n-type -boron doped with V, which is known to preferably occupy A 1 sites, had the highest ZT value.…”

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

“…Both studies showed different results regarding dopant atom site preferences, however they are evidence of rather high solid solubility of such a large transition element in β-rh B. Contrasting data are available for the TE properties of Zrdoped β-rh B showing highly positive (for Zr 1.0 B 105 and Zr 0.8 B 105 [18,25]), and slightly negative (for Zr 1.0 B 105 [26]) values of Seebeck coefficient in the temperature ranges 200 K -300 K and 300 K -500 K respectively. In view of these inconsistencies and since the structure determination from powder diffraction data of ZrB~5 1 was only of a rather preliminary nature, in the current study we i) aimed to clarify the structure of metal rich Zrdoped β-rh B including the details of boron atom framework and dopant sites preferences as well as we ii) undertook the task to shed a light on the TE properties and their compositional dependence within the studied solubility range.…”