Role of fluorite phase formation in the texture selection of sol-gel-prepared Pb(Zr_1-x,Ti_x)O₃ films on Pt electrode layers

Abstract

Transmission electron microscopy-selected area electron diffraction studies were performed on as-pyrolyzed sol-gel-derived Pb(Zr1-x,Tix)O3 films deposited on Pt electrode layers to elucidate the structural cause behind the large effects of pyrolysis conditions on orientation selection [L. Fè, G.J. Norga, H.E. Maes, and G. Maes, J. Mater. Res. 16, 2499 (2001)]. The crystallinity of the intermediate pyrochlore phase, which forms during pyrolysis, was found to strongly depend on pyrolysis conditions. Specifically, pyrolysis for 10 s at 350 °C was seen to result in conversion of the film to a well-crystallized, oxygen-deficient pyrochlore phase with the fluorite crystal, structure (disordered pyrochlore). We speculate that formation of the metastable fluorite phase is favored by the reduced oxygen partial pressure, caused by burnoff of residual acetates. Longer pyrolysis times and/or higher pyrolysis temperatures result in a quasi-amorphous intermediate phase. The presence of the well-crystallized fluorite phase in the pyrolyzed film is seen to result in (111)-oriented films after crystallization, while pyrolyzed films consisting of a quasi-amorphous intermediate phase turn out (100) or mixed (100)/(111) oriented after crystallization. An explanation for the observed orientation effects, on the basis of the different surface energetics of fluorite versus perovskite structure oxides, is proposed.