Phase formation and thermoelectric properties of FeSe2–CoSe2 system.

The phase formation and thermoelectric transport properties of FeSe 2 –CoSe 2 systems were investigated by synthesizing a series of (Fe 1–x Co x)Se 2 polycrystalline alloys (x = 0, 0.25, 0.5, 0.75, and 1). It was observed that as x increased from 0 to 0.5, lattice parameters increased while the orthorhombic structure of FeSe 2 was retained. The bipolar conduction behavior of FeSe 2 (x = 0) changed to n -type conduction at all measured temperatures. The electrical conductivity is greatly increased with x , and the largely enhanced power factor of 1.37 mW/mK2 at 600 K is seen for Fe 0·5 Co 0·5 Se 2 (x = 0.5) compared to 0.37 mW/mK2 for FeSe 2. As x is further increased to 0.75 (Fe 0·25 Co 0·75 Se 2), the cubic phase of CoSe 2 started to form and no further enhancement of power factor is seen. Lattice thermal conductivity is gradually decreased to 3.18 and 1.79 W/mK Fe 0·75 Co 0·25 Se 2 (x = 0.25) and Fe 0·5 Co 0·5 Se 2 (x = 0.5) at 600 K, compared to 4.36 W/mK for x = 0 (FeSe 2). Consequently, the thermoelectric figure of merit zT at 600 K for Fe 0·75 Co 0·25 Se 2 (x = 0.25) and Fe 0·5 Co 0·5 Se 2 (x = 0.5) is greatly enhanced to 0.14 and 0.16, respectively, compared to 0.05 for x = 0 (FeSe 2). [Display omitted] • A series of (Fe 1– x Co x)Se 2 alloys (x = 0, 0.25, 0.5, 0.75, and 1) was investigated. • Orthorhombic structure of FeSe 2 was retained to x = 0.5. • Lattice thermal conductivity of FeSe 2 is gradually decreased to x = 0.5. • Power factor is maximized for x = 0.5 • Thermoelectric figure of merit is optimized for Fe 0·5 Co 0·5 Se 2 (x = 0.5). [ABSTRACT FROM AUTHOR]