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

Abstract

Samples of 1 at% metal (Al, Co, Cr, Cu, Mo, Nb, Ni, Ru, Si, V, W, Zr)-doped -rhombohedral boron (-boron) were prepared by spark plasma sintering and their thermoelectric properties were examined in the temperature range from 353 K to 1073 K. It was found that V-dopedboron exhibited the largest dimensionless figure of merit (ZT value). The V concentration dependence of the thermoelectric properties ofboron was investigated. We discuss the effects of V doping into -boron and the precipitation of a second phase on the thermoelectric properties. The temperature dependences of electrical conductivity and the Seebeck coefficient in the single-phase range of V concentration can be explained by assuming a combination of the band conduction of holes and the variable-range hopping conduction of electrons. This is described using the band structure model with the intrinsic acceptor level and the hybridization between the orbitals of boron and V, which corresponds to the metallic-covalent bonding conversion. Among the samples of V-doped -boron, V 2:0 B 105 had the highest value of ZT (7:91 Â 10 À3 at 1079 K) due to both V doping and the precipitation of a metallic phase (VB 2 ).

n-p Type variation in thermoelectric AlMgB14–based materials by raw material mixture ratio

“…Though various higher-boride thermoelectric materials have been developed to date, there are few report about ntype higher-boride materials [14e16]. Kim and Kimura reported that b-rhombohedral boron exhibited a change of Seebeck coefficient between positive and negative along with vanadium doping [17]. Maruyama et al reported to control of sign of Seebeck coefficient on YAlB 14 the structure of which is similar to that of AlMgB 14 [18] by controlling metal occupancy [15].…”

p-n Control of AlMgB14-Based Thermoelectric Materials by Metal Site Occupancy

“…However, most B 12 icosahedral cluster solids have comparatively high thermoelectric properties at a high temperature, making them promising high-temperature thermoelectric materials. However, most B 12 icosahedral cluster solids are p-type materials and the development of an n-type material to create a pair is desirable [ 16 , 21 , 22 , 23 , 24 ].…”

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

“…Regarding elemental boron, the structure of βrhombohedral (β-rh) B (space group m R3 ) [7][8][9][10][11] has been extensively studied with respect to its ability to accommodate interstitially different kinds of foreign atoms [12][13][14]. It has been shown that metal doping into β-rh B can control the bonding nature in and between the clusters, delivering variation of physical properties such as electrical and thermal conductivities and Seebeck coefficient [13,[15][16][17][18][19][20]. The interstitial doping of β-rh B by certain 3d-metals (e.g.…”

“…V, Cr, Fe, Ni, Cu) led to negative values of TE power in the originally p-type semiconducting material in certain temperature ranges [13,21]; the structural and electronic properties of some solid solutions (i.e. V:B, Fe:B, Cu:B) have been consistently studied by different research groups [13,15,22,23].…”