Pure and Doped SrTiO<sub>3</sub> Powders Obtained by Ultrasonic Synthesis

Abstract

Thermoelectric ceramics are those capable of converting thermal into electricity energy by the Seebeck effect. The non-conventional synthesis of ceramic powders and the doping of these powders with rare earth elements are factors that can improve the efficiency in energy conversion. The objective of this work was to synthesize and analyze pure and doped SrTiO3 powders by solid state reaction (SSR) and ultrasonic synthesis (USS). The precursors of SSR were: strontium carbonate (SrCO3), titanium oxide (TiO2) and lanthanum and neodymium oxide (La2O3 and Nd2O3). They were mixed in a ball mill for 3.5h in stoichiometric ratio to obtain SrTiO3 (STO), Sr0.96La0.04TiO3 (STO-04La), Sr0.96Nd0.04TiO3 (STO-04Nd) and Sr0.96La0.02Nd0.02TiO3 (STO-02La02Nd). The powder mixtures were calcined at 1000°C in a conventional oven for 2h. The USS powders were produced by solubilization of Ti (C4H9O)4 and SrCO3 in an HNO3 aqueous solution. The solution was precipitated with NH4OH and, then, this powder was dried at 70°C for 24h, in air. The dried powder was added to a solution of KOH and subjected to ultrasound irradiation. The same procedure was followed for the synthesis of USS doped powders, STO-04La, STO-04Nd, and STO-02La02Nd powders using as dopant lanthanum and neodymium oxides. The powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and crystallite sizes were calculated by the Scherrer equation to evaluate the differences on structural and microstructural properties.