Raman Scattering in the Aurivillius-Layered Ferroelectric SrBi_2Ta_2O_9 - Bi_3TiNbO_9 Thin Films

摘要

We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi_2Ta_2O_9)_x(Bi_3NbO_9)_(1-x) layered structures and to compare them with the correspond-ing bulk materials. Various compositions, with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, were prepared by metal organic solution deposition method on Pt/TiO_2/SiO_2/Si substrates. A topographic micro-Raman study revealed very homogeneous films at each composition. The Raman spectrum of x = 0.0 film shows bands around 170, 232, 337, 522, 608, 677 and 832 cm~(-1), which indicates Bi_3TiNbO_9 formation. The evolution of the Raman bands with the inclusion of SBT material shows frequency shifts and a broadening of the bands due to the differences in mass between Sr and Bi in the A-sites, and Ta, Ti, and Nb in the B-sites. A lower degree of crystallization was found in the films compared to the bulk due to the presence of stress in the films. Strong contributions from defects were also observed in the temperature-dependent Raman spectra.