Incorporation of copper in LaCoO3: modulating thermoelectric power factor for low- and mid-temperature thermoelectric applications

In the present work, LaCoO3/ x wt% Cu (x = 0%, 5%, 10%, 15%, and 20%) samples were prepared using solid-state reaction method followed by conventional sintering. We have performed electrical and thermoelectric (TE) measurements on these samples both at low (100–310 K) as well as in mid (310–790 K) temperature range. X-ray diffraction (XRD) studies showed that the pristine LaCoO3 sample crystallized in a distorted rhombohedral structure with the space group R3-c\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R\stackrel{-}{3}c$$\end{document}. Interestingly, the addition of Cu resulted in two distinct phases viz. rhombohedral LaCoO3 and monoclinic CuO. Throughout the entire temperature range, the electrical resistivity of the samples decreased with temperature, which depicts the semiconducting behavior of the prepared samples. Furthermore, there is a crossover from negative to positive Seebeck coefficient for the pristine sample at 275 K, but all the copper-incorporated samples exhibited a positive Seebeck coefficient indicating holes as the majority charge carriers. It is found that, the sample with x = 10% exhibited the maximum power factor of about 99 µW/m K2 at 400 K, which is significantly higher than the pristine sample at the same temperature.