High thermoelectric power factor in Cu–Ni alloy originate from potential barrier scattering of twin boundaries

Abstract

Constantan alloy (Cu–Ni) has been known for a long time in thermocouples due to its thermal power property. In this study, we show an enhancement in thermoelectric performance of Cu56Ni42Mn2 alloy by introducing nanoscale twins into its microstructure. Comparing to arc-melted ingot (without nanoscale twins), the ball milled and hot pressed (BM–HP) samples with twinning showed a higher Seebeck coefficient of ~−72.5μVK−1 (an increase of ~12% at 873K), a larger power factor of ~102μWcm−1K−2 (an increase of ~21% at 873K), and hence a higher ZT of ~0.19 (an increase of ~34% at 873K). A high output power density of ~53.4Wcm−2 is calculated from the high power factor even though the conversion efficiency is lower than 3% due to the low ZT. TEM characterization shows there is a large quantity of nanoscale twins with spacing of 50–200nm. It is very likely that low-energy carriers are selectively scattered by the twin boundaries (i.e., potential barrier scattering) thus lead to enhanced Seebeck coefficient. The improved thermoelectric performance of nano-twinned Cu–Ni alloy suggests constantan could be promising in thermoelectric power generation where the power output density is more important than the conversion efficiency.