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Micro-Raman spectroscopy and X-ray diffraction have been used to explore thelattice dynamics of Nb-substituted SrBi2(Ta1-xNbx)2O9 (SBTN) crystalline thinfilms annealed at low temperature, 700oC. It turned out that SrBi2(Ta1-xNbx)2O9films consist of fine-grained spherical structures for x=0.1-0.4, while theformation of rod-like grains occurs for x=0.5 due to the stress-inducedtransformation of the thin film perovskite structure. Moreover, it was revealedthat during Nb cationic substitution Aurivillius phase formation was enhancedand become dominated in SBTN thin films and fluorite/pyrochlore phase formationwas highly suppressed. We assume that these changes are conditioned by theferrodistortion occurring in ferroic perovskites, namely by the tiltingdistortion of (Ta,Nb)O6 octahedra for x=0.2-0.5. The octahedral tiltingdistortion can change the coordination environment of the A-cite cation, aswell as it lowers the SBTN symmetry due to the differences in ionic radius andmass between Ta and Nb in the B-sites, that can lead to significant changes ofthe SBTN crystal structure. The same nonmonotonic trends were observed for theferroelectric perovskite phase fraction and remanent polarization on Nb contentin SBTN films. The substituting Nb atoms with a concentration of 10-20 % madeit possible to increase the remanent polarization in 3 times and raise theperovskite phase fraction from 66% to 87%. Therefore, obtained results can beused for the production of lead-free thin films with a high remanentpolarization under low annealing temperature, being promising for advancednonvolatile random access ferroelectric memory (NvFeRAM) applications.  Keywords: ferroelectric, sol-gel method, perovskite structure,crystallization annealing, defects, remanent polarization, SBTN films, Ramanspectroscopy, Landau-Devonshire approach.

Enhanced ferroelectric properties of low-annealed SrBi2(Ta,Nb)2O9 thin films for NvFeRAM applications