Phase transformation studies of ceramic BaTiO3 using thermo-Raman and dielectric constant measurements

Abstract

Ferroelectric phase transformation characteristics of ceramic BaTiO3 have been studied by combined thermo-Raman and dielectric measurements. The temperature dependence of Raman bands at 311 and 721 cm−1 shows that tetragonal to cubic (T–C) phase transformation occurs over a range of temperature. The increase in the bandwidths of these bands indicates that this transformation is an order-disorder transformation. The differential thermo-Raman intensity thermograms show a dip at a temperature corresponding to the maximum rate of phase transformation and this temperature can be defined as phase transformation temperature Tp. The ferroelectric transformation temperature Tm corresponding to the peak in the ε(T) obtained from the temperature dependence of dielectric constant is found to coincide with Tp. This indicates that maximum in dielectric constant occurs at the maximum rate of T–C phase transformation. Both Tp and Tm exhibit thermal hysteresis. The Curie temperature TC obtained from the intersection of tangential of inverse dielectric constant to the temperature axis and is found to be less than Tm and Tp in agreement with O. G. Vendik and S. P. Zubko [J. Appl. Phys. 88, 5343 (2000)] calculations. Thermo-Raman spectroscopy coupled with dielectric constant measurement is shown to be an effective technique to investigate the phase transformation in ferroelectric materials.

Raman and AFM piezoresponse study of dense BaTiO3 nanocrystalline ceramics

“…2) show all the main characteristics of the Raman activity in single-crystals and in coarse ceramics, [14][15][16] proving the existence of all the polar phases and the succession of transitions rhombohedral-orthorhombic-tetragonal-cubic (r-o-t-c) of BT, with some differences in the temperature range of stability of each phase. The main spectral features observed for 50 nm BT ceramics are: (a) two intense broad bands A1(TO1) at ∼265 cm −1 (which is a stiffened component of the soft mode phonon) and A1(TO4) at ∼513 cm −1 , (b) a sharp peak (silent) at ∼306 cm −1 (TO3-LO3) and the LO4 band at ∼717 cm −1 , both stable up to high temperatures in the c phase, (c) a small peak E(TO4) at ∼487 cm −1 present only in r and o phases, (d) E(TO1) and unresolved TO2-LO2 peaks at ∼166-186 cm −1 and some continuous scattering between the TO1 and TO2 modes even in the cubic phase, which was not observed in the coarse grained ceramics, 17 (e) a small broad mode ∼650 cm −1 not present in single crystal and coarse ceramics, but also found in polycrystalline films, 17 which was considered as being activated by a high degree of granularity in these systems.…”

Grain size and grain boundary-related effects on the properties of nanocrystalline barium titanate ceramics

“…[28][29][30][31][32] In the cubic phase, the BT lattice dynamics is strongly anharmonic and the soft mode is overdamped. [28][29][30][31][32][33][34][35] At the C-T phase transition, the triply degenerate soft mode splits into well-separated components A1(TO1) and E(TO1) at ∼260 and ∼50 cm −1 , respectively. 32 In the T phase, the overdamped Ecomponent of the soft mode (responsible for the high dielectric anisotropy at room temperature) continues its softening down to the T-O transition, when the double-degenerate E-component splits into B1 (∼250 cm −1 ) and overdamped B2 (∼60 cm −1 ) components.…”

High frequency dielectric relaxation in lanthanum modified PbTiO3 ferroelectric ceramics

“…This could suggest the existence in the material of polar regions for temperatures higher than the transition temperature. It is not yet clear to us whether or not this fact could be one more evidence of the contribution from an "order-disorder" type ferroelectric-paraelectric phase transition in ABO 3 perovskite structures, as recently reported in the literature [13][14][15] . Further studies are in course in order to closely treat this question.…”