Geothermal and solar heat can be directly converted into electricity by using thermoelectric generators. Perovskite-type metal oxides are potential materials to improve the efficiency of these devices. Cobaltates with p-type conductivity and n-type manganates are considered for the development of a ceramic thermoelectric converter. Sintered pellets and thin PLD films with the composition La1-xCaxMO3-delta (x = 0, 0.3, 0.4) (M = Co, Mn) were synthesised and characterised concerning their thermoelectric properties in a broad temperature range. It was found that similar to polycrystalline samples the electrical conductivity of LaCoO3 increases significantly with 40% Ca-substitution due to the formation of Co4+ ions while the thermopower decreases. The thermopower values of the La0.8Ca0.2MnO3-delta films have a negative sign, but become large and positive at temperatures of 1000 K. (c) 2007 Elsevier Ltd. All rights reserved.