Raman Study of Low-Temperature Phase Transitions in Polycrystalline Bi₄Ti₃O₁₂ Thin Films

Polycrystalline Bi₄Ti₃O₁₂ thin films were prepared on fused quartz substrates by pulsed laser deposition. The films were crystallized in the orthorhombic layer perovskite structure confirmed by x-ray diffraction and Raman spectroscopy. The two broad Raman bands centred at 57 and 93cm^-1 at 300K break up into clusters of several sharp Raman peaks at 90K. The temperature dependence of Raman spectra indicates the occurrence of monoclinic distortion of orthorhombic structure at low temperature in the as-prepared Bi₄Ti₃O₁₂ thin films.