Aikebaier Yusufu

Thermoelectric properties of Ag1−xGaTe2 with chalcopyrite structure

In the present study, we investigated the high-temperature thermoelectric (TE) properties of AgGaTe2 with chalcopyrite structure. We tried to enhance the TE properties of AgGaTe2 by reducing the Ag content. The reduction of Ag increased the carrier concentration, leading to enhancement of the dimensionless figure of merit (ZT). The maximum ZT value was 0.77 at 850 K obtained in Ag0.95GaTe2, which was approximately two times higher than that of stoichiometric AgGaTe2.

Thermoelectric Properties of Chalcopyrite-Type CuGaTe2 with Ag Substituted into the Cu Sites

CuGaTe2 has recently been reported to have a high thermoelectric (TE) figure of merit (ZT) of 1.4 at 950 K [T. Plirdpring et al.: Adv. Mater. 24 (2012) 3622]. However, the ZT values of CuGaTe2 in the low and middle temperature ranges are not high, due to high lattice thermal conductivity (κlat) in those temperature ranges. We have attempted to reduce the κlat of CuGaTe2 by the substituting Ag into the Cu sites. Polycrystalline samples of Cu1-xAgxGaTe2 (x = 0, 0.25, 0.5, 0.75, and 1) were prepared and the TE properties were examined. Ag substituted reduced κlat and changed the carrier concentration and mobility, which improved ZT in the low and middle temperature ranges; a ZT value of 0.7 was obtained at 700 K for Cu1-xAgxGaTe2 with x = 0.5, which is 40% higher than that of CuGaTe2.

Improving thermoelectric properties of bulk Si by dispersing VSi2 nanoparticles

In order to enhance the thermoelectric properties of Si-based bulk materials, the lattice thermal conductivity (κlat) should be reduced with little degradation of the electrical properties. Our group had previously demonstrated that the phosphorus (P)-rich nanoscale precipitates formed naturally in heavily P-doped bulk Si scatter phonons more effectively than carriers, resulting in a high figure of merit (ZT) [A. Yusufu et al., Nanoscale 6, 13921 (2014)]. Here, we successfully prepared heavily P-doped bulk Si containing metallic VSi2 nanoparticles through the ball milling of Si, V, and P and subsequent spark plasma sintering. The VSi2 nanoparticles did not affect the electrical properties of Si significantly but greatly decreased the κlat, leading to a marked increase in ZT. The maximum ZT value, which was 0.4, was obtained at 1073 K, which is two times higher than that for Si.

Thermoelectric properties of Si/SiB3 sub-micro composite prepared by melt-spinning technique

This study presents a new self-assembly process to form a fine structure in bulk Si. We fabricated a semiconducting composite material consisting of sub-micro-sized (100–500 nm) SiB3 precipitates distributed in a Si matrix whose grain size was on the order of microns. The sub-micro-sized SiB3 particles were precipitated during the spark plasma sintering process of a metastable Si-B (Si:B = 92:8) supersaturated solid solution prepared by the melt-spinning technique. The composite was a heavily doped (5 × 1020 cm−3) p-type semiconductor. The SiB3 precipitates did not affect the Seebeck coefficient, slightly reduced the carrier mobility, and greatly reduced the lattice thermal conductivity. Specifically, the lattice thermal conductivity was reduced by 44% compared with that of p-type Si without precipitates at room temperature. The SiB3 precipitates improved the thermoelectric figure of merit ZT from 0.17 to 0.23 at 1073 K, which indicates that the formation of small precipitates effectively improves the the...