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

Orientation-controlled epitaxial thin films of bismuth layer-structured fer roelectrics, SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN), were prepared on single -crystal SrTiO3 (STO) substrates by the coating pyrolysis process. Most of the SET (SBN) films showed the (106) and (001) orientations on STO(110) and (001), respectively. The degree of orientation, in terms of the ratio of p eak intensity to the background level in the x-ray diffraction phi-scan pro file for the film, greatly increased with a decrease in the oxygen partial pressure, p(O-2), of annealing atmosphere at 800 degrees C. Interestingly, coexistence of the (110)-oriented grains with the (106)-oriented ones on ST O(110) [and the (100)-oriented grains with the (001)-oriented ones on STO(0 01)] was observed exclusively in the SET films annealed at 700-750 degrees C under p(O-2) of 10 Pa. Atomic force microscopy observations showed that t he surface morphology of the SET films remained almost unchanged, i.e., com prising round-shaped grains of submicrometer size, whereas that of the SBN films drastically changed, according to the variation in orientation of sub strate surfaces or in annealing conditions, i.e., temperature, p(O-2), and time.