Isovalent doping of Cu2+ induced elastic strain on cobalt spinel oxides for enhancing room temperature thermoelectric application

A novel thermoelectric material , Cu x Co 1-x Al 2 O 4 (x=0.02–0.10) was developed using a microwave combustion method with urea as the fuel source and investigated for the room temperature thermoelectric applications. The spinel phase was analyzed using XRD , and the spinel Co-O-Al bond were identified at the band region of 779 cm −1 in the FT-IR spectrum. SEM revealed a marigold flower like pattern in the morphology, while TEM showed a cubic morphology, and elemental composition are confirmed by EDAX . Additionally, optical characteristics of the pristine and Cu doped samples were thoroughly analyzed by UV- DRS spectroscopy. EPR measurement confirmed the presence of free electrons which are crucial for electrical conductivity . XPS analysis further verified the oxidation states of each element. To investigate the thermoelectric properties of CoAl 2 O 4 and Cu x Co 1-x Al 2 O 4 (x=0.02–0.10), hall measurements were conducted, revealing the highest carrier concentration was found as 8.728×10 16 cm −3 for Pristine CoAl 2 O 4 . Notably, the highest electrical conductivity was found as 2.48×10 −2 Scm −1 , while the lowest thermal conductivity measured was 0.0522 W/mK for Cu 0.10 Co 0.90 Al 2 O 4 . The Seebeck co-efficient for the pristine sample was 730 μV/K, which decreased to 427 μV/K for Cu 0.10 Co 0.90 Al 2 O 4 . The highest power factor observed was 5.1 nWcm −1 K −2 for Cu 0.10 Co 0.90 Al 2 O 4 . This study presents the obtained results and the fabrication of a wearable device using p-type (CoAl 2 O 4 ) and n-type (Cu 0.10 Co 0.90 Al 2 O 4 ) materials, achieving an output of 3.6 mV with a temperature difference of 1.5 K”.