Entirely aqueous solution-gel route for the preparation of (Pb1-xCax)TiO3 thin films

Abstract

In this work, calcium-modified lead titanate (Pb1-xCax)TiO3 (PCT) precursor solutions with different amounts of Ca2+ substituting Pb2+ (x = 0.24 and 0.50) have been prepared for the first time by an entirely aqueous solution-gel route. The use of water as a nonhazardous and inexpensive solvent, together with the easy handling of the technique (no inert atmosphere is required), are the major advantages of this method. A stable citrato-peroxo complex of Ti(IV) was synthesized first and subsequently combined with the Pb2+ and Ca2+ reagents (citrates) in the desired molar ratio to obtain the aqueous precursor solutions. The stability of these solutions with time is slightly influenced by the amount of Ca2+ introduced in the PCT system. Gels were obtained from these solutions and subjected to thermogravimetric analysis coupled on-line to Fourier transform infrared (TGA-FTIR) and mass spectroscopy (TGA-MS) techniques. To prepare thin films, we had to improve the hydrophilicity of the Pt/TiOx/SiO2/Si substrates and hence their wetting by the aqueous solutions using a wet chemical treatment of cleaning. Crystallization of the films was carried out by rapid thermal processing (RTP) in air at 650 degrees C. Films with a single perovskite phase and a homogeneous microstructure were thus obtained, as deduced by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ability of this solution method to obtain PCT films with ferroelectric and dielectric responses is also demonstrated in the present work.