Phase evolution of perovskite PZT nanotubes caused by metal ion diffusion

We report the phase evolution of Pb(Zr_0.52Ti_0.48)O₃ nanotubes (PZT-NTs) caused by ion diffusion. The PZT-NTs were fabricated in pores of porous anodic alumina membrane (PAAM) using a spin coating of PZT sol-gel solution and subsequent thermal annealing under oxygen atmosphere. The surface morphology and composition of PZT-NTs were examined as a function of the annealing temperature, and the diffusion of elements over nanometer length scales was investigated based on analyses using field emission transmission electron microscopy (FETEM), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDX). STEM analyses with EDX line profiles provide a characterization of the interface between PZT-NT and PAAM, suggesting that Pb, Zr, and Ti diffused into the PAAM. The diffusion results in the secondary phase in the PZT-NTs, such as the pyrochlore phase of Pb-deficient. TEM analyses suggest that the interface was mostly lead aluminate, such as Pb₂Al₂O₅ or PbAl₁₂O₁₉, or aluminum titanate like Al₂TiO₅. These results indicate that considerable diffusion of metal ions occur, and furthermore such diffusion brings great difficulties in the phase control of metal oxides.