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Lanthanum cobaltate, LaCoO3, with a perovskite type of structure has been recognized as attractive thermoelectric material due to its high Seebeck coefficient (S>500 V/K at room temperature) and high thermal stability. However, the electrical resistivity of LaCoO3 is relatively гigh (about 10 Ωcm at 300 K), which lowers the thermoelectric activity (ZT

Ca3Co4O9 ceramic is an attractive lead-free alternative to conventional semiconductor materials, based on bismuth and tellurium with a practical application in converting waste heat to electricity, solar thermoelectric generators and refrigeration devices [1]. Ca3Co4O9 is a thermoelectric material representing the family of the so-called misfit layered oxides. It consists of a Ca2CoO3 layer which is an insulating subsystem that maintains the charge supply for the conducting CoO2 layer, where both Co3+ and Co4+ ions coexist [2]. In addition to the research carried out on the thermoelectric properties of Ca3Co4O9, several studies have reported results elucidating crystal information and electronic structure [3,4]. Recently, a giant dielectric permittivity was measured in Ca3Co4O9 ceramic at room temperature [5]. In this work, we investigated and compared the structural and electrical properties of Ca3Co4O9 (CCO) ceramics and thin films. The CCO thin films were produced from a stoichiometric, in-house made CCO ceramic by pulsed laser deposition (PLD) onto (100) oriented lanthanum aluminate (LaAlO3, LAO) substrates. Both the CCO ceramics and thin films were subsequently characterised by X-ray diffraction (XRD). To evaluate the samples’ dielectric properties, capacitor structures were formed. Their capacitances were measured and the corresponding permittivities were evaluated in a temperature range RT – 450 K. Both CCO ceramics and thin films were pure misfit phases. The thin film exhibited epitaxial growth with preferred (00l) orientation. For the CCO ceramics, the measured dielectric permittivity was increasing moronically with no maximum observed at temperatures up to 450 K (Figure 1a). The estimated value of the dielectric permittivity ~ 5,300 measured at room temperature corresponds well with the values reported elsewhere [5]. Similar behaviour of the capacitance as a function of the temperature with a maximum at 430K was measured for the thin film sample (Figure 1b). Due to the small thickness of the layer, the error associated with the dielectric permittivity evaluation procedure is very high. Nevertheless, one could speculate that it is in the same order of magnitude as those of the CCO ceramic. The observed reduction of the phase-transition temperature is associated with the residual strain in the thin film sample introduced by the substrate.