Modification of ca3co4o9 thermoelectric performances via processing and doping

Resumen

Thermoelectric (TE) materials can transform a temperature gradient into electricity directly, due to the well-known Seebeck effect. Nowadays, due to the global warming effect, these materials are gaining increased interest for practical power generation applications using natural and waste heat sources. Their performance is usually quantified by the dimensionless figure-of-merit (ZT=S^2T/(rho*kappa) S: Seebeck coefficient, T: absolute temperature, kappa: total thermal conductivity, rho: electrical resistivity). Since 1997, the misfit-layered cobalt oxides (cobaltites) have been found to possess attractive TE properties at high temperatures in oxidative environments. Among the different TE cobaltites, the so-called Ca3Co4O9 compound presents some of the best TE properties and has been extensively studied in the past years, having the largest amount of available information. Ca3Co4O9 has a monoclinic crystal structure, composed of two different alternately-stacked layers (CdI2-type [CoO2] and NaCl-type [Ca2CoO3]) which present a misfit in the b-direction. It has been shown that the TE performances of this system (compound) can be further improved, especially in bulk form, making it a very-promising candidate for practical power generation applications in a not-so-distant future. The main objective of this work has been to study the improvement of the electrical performances (quantified by the power factor, PF=S^2/rho) of bulk polycrystalline Ca3Co4O9 samples, via doping, synthesis and densification.