posted on 2024-03-06, 22:17authored byJoseph
Ngugi Kahiu, Samuel Kimani Kihoi, Hyunji Kim, Ho Seong Lee
Improving the efficiency of upcoming thermoelectric (TE)
materials
and exploring their potential for various niche applications are among
the promising strategies for addressing the challenges that impede
the commercialization of traditional TE materials. This work reports
the results of efforts to improve the performance of the recently
optimized ZrFe0.4Ni0.6Sb double half-Heusler
(DhH) by cobalt (Co) doping. The synthesized ZrFe0.4–yCoyNi0.6Sb
samples exhibit phase separation into coherent biphasic DhH and ZrNiSb
phases with greatly improved electrical conductivity, which increases
from ∼400 S/cm in sample y = 0 to ∼3886
S/cm in sample y = 0.4 at room temperature. In addition
to the suppression of bipolar conduction, the thermal conductivity
also decreases by ∼18% in sample y = 0.1 compared
to sample y = 0, which can be attributed to the enhanced
phonon scattering and leads to an increase in peak zT from 0.33 in
sample y = 0 to 0.37 in sample y = 0.1 at 973 K. Unfortunately, higher doping concentrations not
only deteriorate the Seebeck coefficient but also excessively increase
the electronic and lattice thermal conductivities, leading to lower
zT values in the samples y > 0.1. By synthesizing
and analyzing the (ZrFe0.4Ni0.6NiSb)1–z + (ZrNiSb)z samples,
it is confirmed that the ZrNiSb phases are responsible for the appalling
TE performance in the y > 0.1 samples. Further
investigation
using the recently restructured single parabolic model shows that
the ZrFe0.4Ni0.6NiSb system was already overdoped
before Co doping, which explains the reason for the resulting PF decrease.
Finally, the ferromagnetic nature and tunable magnetism of the synthesized
samples are revealed by using a vibrating sample magnetometer to study
their magnetism, expanding their range of potential niche applications
in spintronics.