Effect of heating rates on the crystallization process of (111)-oriented lead zirconate titanate thin films prepared by the sol–gel method

Abstract

We prepared Pb(Zr0.52Ti0.48)O3 (PZT) thin films with a (111)-preferred orientation on Pt/Ti/SiO2/Si substrates by a sol–gel method, and investigated the effects of heating rates on the crystallization process and kinetics by X-ray diffraction, transmission electron microscopy and Avrami׳s model. We found that the (111)-orientated initial crystallites directly formed on the top of Pt in the early stage of crystallization, and had smaller lattice parameters and an enhanced Ti content than the standard perovskite PZT. The quantity and distribution of the initial crystallites were dependent on the heating rates. The initial crystallite acted as a nucleation site for the perovskite PZT, which grew with a columnar grain structure into the pyrochlore matrix throughout the film. Using Avrami׳s model, we found that the effective activation energy for crystallization of the PZT films heated at a fast heating rate of 35°C/s to be 241kJ/mol, much lower than 325kJ/mol for crystallization of the PZT films heated at a low heating rate of 25°C/min. These results show that a fast heating rate in annealing process can reduce the effective activation energy for crystallization, improve the microstructure including the crystalline orientation, grain size and shape and thus the electrical properties of PZT thin films.