On the phase transformation kinetics in lead scandium tantalate thin films

The phase transformations from amorphous to pyrochlore to perovskite in lead scandium tantalate (PST) thin films during a rapid thermal annealing (RTA) process have been studied. Volume fractions for pyrochlore and perovskite were obtained from their respective x-ray diffraction intensities. Two models assuming the starting phase being either pure amorphous or pyrochlore were analysed in detail. Equations have been derived and numerical calculations have been used to simulate the volume fractions for each phase as functions of annealing time. Transformation parameters k and n were obtained by comparing the simulated to the experimental volume fractions using a least-squares curve fitting technique. Transmission electron microscopy, SEM and energy dispersive x-ray spectroscopy were employed to study the lead loss and other factors affecting phase transformations. It is concluded that the starting materials in the PST films deposited at 300°C were mixture of amorphous and pyrochlore and the phase transformations upon RTA are diffusion limited.