Nanoindentation study of Cu doped NaCo2O4 ceramics

Abstract

Thermoelectric materials, such as layered cobalt oxides, have been the subject of many theoretical and experimental investigations in past decade as potential candidates for application in energy conversion. In this work, polycrystalline samples of NaCo2-xCuxO4 (x = 0, 0.01, 0.03, 0.05) were synthesized from the powder precursors obtained by the citric acid complex method (CAC) and mechanochemically assisted solid state reaction method (MASSR). The obtained powders were uniaxially pressed into disc-shaped pellets and subsequently sintered at 880 °C in inert argon atmosphere. Indentation experiments were carried out to investigate mechanical properties. The hardness (H) and the Young's modulus of elasticity (Y) were determined using Agilent Nanoindenter G200. The surface approach velocity of the indenter (Berkovich pyramid) and Poisson ratio were set to 10 nm/s and 0.25, respectively. It was found that the highest Y (65.2 GPa) and H (1.41 GPa) were obtained for the CAC sample containing 1mol% of Cu. These results indicated a significant improvement of mechanical properties even in the case of the sample with the lowest dopant concentration.