Thermoelectric properties of Ca3Co4O9 thin films grown by pulsed-laser deposition

The Ca3Co4O9 (CCO) compound consists in a misfit layered structure formed by superposition of two atomic planes (Ca2CoO3 and CoO2) that makes this oxide a promising material for thermoelectric (TE) application. The thermal and electrical conductivities and the thermoelectric power can be tuned by controlling the oxygen deficiency in CCO films. Pulsed-laser deposition (PLD) performed at low oxygen partial pressure allows to grow oxygen deficient films. In that sense smooth, dense, and homogeneous films, with different stoichiometry and crystalline state were prepared by PLD in order to modify charge carrier concentration and thermal diffusivity of material. Thus, nearly stoichiometric and highly oxygen deficient CCO films were deposited onto sapphire substrate hold at room temperature, 300, 500 and 700°C under 10^-1 and 10^-6 mbar in oxygen partial pressure, respectively. The electrical, thermal and thermoelectric properties are correlated to the structural, and morphological characteristics of thin films by using an original equipment (ZT meter) specifically designed for TE measurements on thin films.