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

Abstract

Thin films of barium titanate (BaTiO 3 ; BT) of various thicknesses (20, 60, 120, 160 and 200 nm) were deposited by a modified sol-gel route on M-plane sapphire [Al 2 O 3 : (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 [B 1 + 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 (T C ) was estimated from the temperature dependence of one of the lattice phonon (∼310 cm −1 ) wavenumber position (!, cm −1 ) and linewidth (0, 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 T C 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 T C is discussed using the conventional Landau-Devonshire theoretical formulation.

Influence of substrates on the statical and dynamical properties of ferroelectric thin films

“…The explanation of the broadened peak can be also the greater damping effects in thin films (Fig. 5) compared to the bulk case [42] what is in agreement with the experimental data [17,41]. The peak becomes narrower and higher with increasing film thickness or when ss J approaches the value of b J (Fig.…”

Characterization of BaTi1−xZrxO3 thin films obtained by a soft chemical spin-coating technique

“…For such compound, the E(2TO) ͑ϳ307 cm −1 ͒ phonon mode indicates an asymmetry within the TiO 6 octahedra, which suggest the presence of a tetragonal crystalline structure. 18 This figure also revealed that the E(2TO) mode become weaker with the increase of the Zr content. Such behavior indicate that the substitution of Ti by Zr in the BaTiO 3 structure results in structural disorder and, consequently, in structural phase transition.…”

Critical behavior of the spontaneous polarization and the dielectric susceptibility close to the cubic-tetragonal transition in BaTiO3

“…Thin films of barium titanate using X-ray diffraction 13 and Raman spectroscopy 13,14 have been studied to investigate the ferroelectric-paraelectric transition. Recently, ferroelectric transition in barium titanate nanoparticles has been studied using NMR spectra.…”

“…21 In order to investigate the temperature and pressure dependence of the dielectric constant (dielectric susceptibility) and the spontaneous polarization close to the phase transitions in BaTiO 3 , the Landau mean field models have been employed. 12,13,15 By expanding the free energy in terms of the order parameter (spontaneous polarization PÞ, the temperature dependence of the P and the dielectric susceptibility (dielectric constant Þ can be obtained by determining the coefficients in the free energy expansion. The temperature dependence of the bilinear coupling constant (order parameter) of the soft-optic and acoustic mode in hexagonal barium titanate has been analyzed using the experimental data 12 according to the prediction of the mean field theory.…”