Enhancing thermoelectric performance of W18O49 through vanadium substitution: A comparative study of VO2 and V2O5 dopants

The tungsten oxide Magnéli phase, W 18 O 49 , is a promising material for thermoelectric (TE) applications due to its high electrical conductivity, σ, and relatively low thermal conductivity, κ.To improve the TE performance, the Seebeck coefficient, S, should be increased by lowering the electron carrier concentration.In this study, we attempted to substitute a lower-valence cation, V 4+ /V 5+ , for W 5+ /W 6+ in W 18 O 49 .The V-doped samples were synthesized by reacting W 18 O 49 and VO 2 (V 4+ ) or V 2 O 5 (V 5+ ) according to the cation ratio, W 1-x V x (x = 0, 0.05, 0.10, 0.15), followed by spark plasma sintering.The V-doped samples exhibited lower σ and larger S compared to the pristine sample, indicating the reduction in the carrier concentration.The doping effect is more pronounced for the V 2 O 5 dopant, leading to the enhancement of the power factor, σS 2 , to 0.73 mW K -2 m -1 .The V doping resulted in the reduction of not only the electronic contribution but also the lattice contribution to κ .The latter result is likely due to the phonon scattering by point defects at the W/V sites and the grain boundaries between the W 18 O 49 -based phase and secondary phases caused by the substitution.The highest dimensionless figure of merit, ZT, of 0.22 at 1073 K was achieved for the x = 0.10 sample with the V 2 O 5 dopant.