Variation of orientation and morphology of epitaxial SrBi2Ta2O9 and SrBi2Nb2O9 thin films via the coating-pyrolysis process

Abstract

Orientation-controlled epitaxial thin films of bismuth layer-structured ferroelectrics, SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN), were prepared on single-crystal SrTiO3 (STO) substrates by the coating-pyrolysis process. Most of the SBT (SBN) films showed the (106) and (001) orientations on STO(110) and (001), respectively. The degree of orientation, in terms of the ratio of peak intensity to the background level in the x-ray diffraction φ-scan profile for the film, greatly increased with a decrease in the oxygen partial pressure, p(O2), of annealing atmosphere at 800 °C. Interestingly, coexistence of the (110)-oriented grains with the (106)-oriented ones on STO(110) [and the (100)-oriented grains with the (001)-oriented ones on STO(001)] was observed exclusively in the SBT films annealed at 700–750 °C under p(O2) of 10 Pa. Atomic force microscopy observations showed that the surface morphology of the SBT films remained almost unchanged, i.e., comprising round-shaped grains of submicrometer size, whereas that of the SBN films drastically changed, according to the variation in orientation of substrate surfaces or in annealing conditions, i.e., temperature, p(O2), and time.