Microstructure and thermoelectric properties of p and n type doped β-FeSi2 fabricated by mechanical alloying and pulse plasma sintering

N and p type doped, beta-FeSi2 was obtained by pulse plasma sintering (PPS) of mechanically alloyed Fe, Si with Mn, Co, Al, P as dopants. The consolidated samples were subsequently annealed at 1123 K for 36 ks. SEM observations proved that the samples consolidated by PPS preserve fine grain size of the mechanically alloyed beta-FeSi2 and the low porosity. The results of XRD measurements confirmed for all samples a nearly complete transformation from alpha-and epsilon- into beta-FeSi2 phase after annealing. Their thermal conductivity decreases significantly with the increase of the test temperature in the entire rage of the temperatures of practical meaning. With the exception of the Mn-doped, all samples exhibited a high Seebeck coefficient, with its highest value for FeSi1.95P0.05 exceeding -400 mu V/K up to 550 K. The Mn and Co Fe site dopants revealed a stronger effect on the thermoelectric properties with 0.15 ZT parameter at 773 K for Fe0.97Co0.03Si2 alloy. The thermoelectric properties of PPS sintered samples were compared to the previously reported consolidated by hot pressing and spark plasma sintering. It has been concluded that the pulse plasma sintering offers an alternative to the already explored methods of production of thermoelectric materials. (C) 2019 Elsevier Ltd. All rights reserved.