Mechanochemically assisted solid-state synthesis of Cu substituted thermoelectric sodium cobaltite

Abstract

Polycrystalline samples of Cu substituted NaCo2-xCuxO4 (x=0, 0.01, 0.03, 0.05, 0.1) were prepared using mechanochemically assisted solid-state reaction method starting from the Na2CO3, Co3O4 and CuO powders. Each powder mixture was mechanically activated by grinding for 3 h in a planetary ball mill with ball to powder mixture ratio 20:1, at the basic disc rotation speed of 360 rpm. The asprepared powders were pressed into disc-shaped pellets and subsequently subjected to a heat treatment at 880 °C for 24 h in inert argon atmosphere. Changes in structural characteristics of the samples and particle morphology, caused by Co substitution by Cu, were characterized using X-ray diffraction and scanning electron microscopy, respectively. It should be emphasized that milling process reduced the time necessary for obtaining pure sodium cobaltite. From the results obtained in this study, observed changes in microstructure were correlated with changes in the lattice parameters, indicating the influence of Cu ion incorporation in NaCo2O4 crystal lattice.