Fine-grained lead-free p-type AgSn4SbTe6 thermoelectric materials synthesized by mechanical alloying and spark plasma sintering

Lead-free p-type AgSn4SbTe6 thermoelectric materials were fabricated by a process combining mechanical alloys (MA) and spark plasma sintering (SPS), whose property improvement was realized by simply repeating the MA and SPS processes. It is found that electrical conductivity decreases mainly due to the reduced carrier mobility even though the carrier concentration tends to increase after repeated MA and SPS, provided that the re-MA time is no longer than a certain time. The thermoelectric property improvement is revealed to benefit from enhanced thermopower and decreased thermal conductivity due to refined grains. The maximum thermoelectric figure of merit (ZT) value was raised to 0.92 at 723 K, almost equivalent to the record one reported for this materials fabricated by a melting process. This work indicates that AgSn4SbTe6 alloy is a promising medium-temperature lead-free thermoelectric material and reveals the figure of merit can be enhanced by a simple microstructural refining method.