Synergistic optimization of thermoelectric properties in Cu₂NiSnSe₄ composited with CuO nanoparticles

Quaternary chalcogenides have gained significant attention in thermoelectric (TE) material research for their high thermoelectric conversion efficiency. The present work investigates the optimisation of the thermoelectric performance of Cu₂NiSnSe₄ utilising the energy filtering effect through the incorporation of CuO into a host matrix. The impact of varying the weight percentage of CuO on the TE properties of the nanocomposite materials was studied and compared with that of pristine Cu₂NiSnSe₄. It was observed that the presence of impurity phases significantly enhances phonon-boundary scattering, leading to a substantial decrease in lattice thermal conductivity, particularly in conjunction with the grain boundaries created by the nanocrystals. For pure samples, the maximum power factor was 1480 μW m^-1 K^-2 at 673 K. Stronger phonon scattering at the interface boundaries created between the Cu₂NiSnSe₄ matrix and CuO inclusions resulted in a low thermal conductivity of 1.01 W m^-1 K^-1 for the 10 wt% composite sample. The Cu₂NiSnSe₄/10 wt% CuO composite had a maximum zT of 0.69, which was 1.4 times higher than that of the Cu₂NiSnSe₄ matrix at 673 K. Additionally, an increase in CuO composition resulted in a uniform increase in the Seebeck coefficient and a simultaneous decrease in thermal conductivity, ultimately contributing to the attainment of the highest figure of merit for these materials.