Variation of orientation and morphology of epitaxial SrBi_2Ta_2O_9 and SrBi_2Nb_2O_9 thin films via the coating- pyrolysis process

摘要

Orientation-controlied epitaxial thin films ofbismuth layer-structured ferroelectrics, SrBi_2Ta_2O_9 (SBT)and 5rBi_2Nb_2O_9 (SBN), were prepared on single-crystalSrTiO_3 (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 oforientation, in terms of the ratio of peak intensity to thebackground level in the x-ray diffraction #phi#-scan profile forthe film, greatly increased with a decrease in the oxygen partialpressure, p(0_2), of annealing atmosphere at 800 deg C.Interestingly, coexistence of the (1 10)-oriented grains with the(106)-oriented ones on STO(110) and the (100)-oriented grainswith the (001)-oriented ones on STO(001) was observedexclusively in the SBT films annealed at 700-750 deg C underp(0_2) of 10 Pa. Atomic force microscopy observations showedthat the surface morphology of the SBT films remained almostunchanged, i.e., comprising round-shaped grains ofsubmicrometer size, whereas that of the SBN films drasticallychanged, according to the variation in orientation of substratesurfaces or in annealing conditions, i.e., temperature, p(0_2), and time.