posted on 2018-01-09, 00:00authored byAryan Sankhla, Akash Patil, Hasbuna Kamila, Mohammad Yasseri, Nader Farahi, Eckhard Mueller, Johannes de Boor
Mechanical
alloying by high energy ball milling is an attractive
solid-state technique for synthesizing a diverse range of stable and
metastable materials. We have studied the synthesis of n-type thermoelectric
Mg2Si0.4Sn0.6 solid solution, aiming
for a fundamental understanding of the mechanisms underlying this
synthesis technique. The investigations on powders by XRD and SEM
show that milling leads to welding of Mg and Sn but fracturing of
Si. This fractured Si diffuses into the ductile matrix on longer milling
times resulting in a phase mixture close to the nominal starting composition
after 35 h of milling. However, phase pure material was only achievable
after sintering; hence, the synthesis of Mg2(Si,Sn) is
a two-step process. Furthermore, a thorough study on the effect of
varying synthesis parameters on the thermoelectric properties was
performed. This was done by systematically varying the milling and
consolidation parameters. No strong influence of milling time on the
thermoelectric properties was observed, and just 2 h of milling followed
by compaction was sufficient to obtain a pellet with optimal thermoelectric
properties. Moreover, increasing sinter temperature/time deteriorated
carrier concentration, hence degrading the electronic properties.
Thus, optimized thermoelectric properties were obtained for the powder
consolidated at 973 K/20 min. Mg2Si0.4Sn0.6 synthesized by mechanical alloying achieved a thermoelectric
figure-of-merit zTmax ∼ 1.4.