Investigations of micro‐stress and phase transition in sol–gel‐derived multideposited coatings of barium titanate using Raman spectroscopy

Abstract

AbstractThin films of barium titanate (BaTiO3; BT) of various thicknesses (20, 60, 120, 160 and 200 nm) were deposited by a modified sol–gel route on M‐plane sapphire [Al2O3 : (1010)] substrates. Raman spectroscopy (RS) and x‐ray diffraction (XRD) were used to evaluate the stress and structural changes with respect to film thickness and establish a correlation. Raman bands and x‐ray peak intensities of 20 nm thick films were too weak to reveal any structural information. Structurally, all other films showed a polycrystalline nature and the average grain size increased with increasing thickness. From the changes in the lattice parameters and one of the Raman modes [B1 + E (TO)], an inverse relation between the compressive stress and film thickness was found at room temperature. Excellent agreement was found for stress values from both measurements. The ferroelectric to paraelectric phase transition (TC) was estimated from the temperature dependence of one of the lattice phonon (∼310 cm−1) wavenumber position (ω, cm−1) and linewidth (Γ, cm−1). This is one of the phonons belonging to the tetragonal phase. For thin films, these ‘order parameters’ did not show apparent anomaly and were qualitatively evaluated from the loss of intensity of this mode. The values of TC in thin films differ from those of the bulk counterpart. Almost an exponential decrease in the stress was observed with increasing thickness for the films due to the structural changes or lattice parameter relaxation. This behavior of TC is discussed using the conventional Landau–Devonshire theoretical formulation. Copyright © 2002 John Wiley & Sons, Ltd.