Raman spectroscopic study of phase transitions in undoped morphotropic PbZr_1−xTi_xO₃

Abstract

Several PbZr 1−x Ti x O 3 (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15-800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long-range or short-range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral-monoclinic-tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high-T and low-T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low-T and high-T Raman scattering spectra were collected on undoped PbZr 1−x Ti x O 3 with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long-range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low-T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions.

Effect of off-center ion substitution in morphotropic lead zirconate titanate composition

“…1insets (a-c) affected by the existence of the ferroelectric phase. 17,18,15 All of the identified modes except E+B1 were found to soften with the rise in temperature. 19 Above 460 K all the modes undergo significant damping, and A1 (1TO) and A1 (2TO) soft modes lose their intensities and disappear,which can be considered as arising from a displacive phase transition in which the ferroelectric tetragonal to paraelectric cubic symmetry distortion commences at temperatures below the disappearance of ferroelectric ordering.…”

Structure and properties of Fe-modified Na0.5Bi0.5TiO3at ambient

“…In relaxor or morphotropic ferroelectrics with short-range phase segregation, Raman signals from second phases of nanometer scale but with the same correlation length are superimposed on the overall signal belonging to a macroscopic matrix phase. [16][17][18][19] Raman spectroscopy has been used to study phase transitions and the nanoscale structural characteristics of NBT and its solid solutions. 15,[20][21][22][23][24] Due to challenges of intrinsic broadening and overlapping of phonon modes in the assignment of mode symmetries, structural analysis thus relies on analyzing soft-mode or hard-mode behavior as a function of composition, pressure or temperature.…”

Dynamical coupling inPb(Zr,Ti)O3solid solutions from first principles

“…For example, the so-called structural mode (that can be thought as the soft-mode of AFD motions) of SrTiO 3 interacts with a polar mode, leading to its observation in the complex dielectric or Raman spectra 10,11 below a critical temperature (below which the structural phase simultaneously exhibits long-range-ordered tilting of the oxygen octahedra and a spontaneous polarization). It is also believed 12,13 that the additional mode appearing below ≃ 200 K in the Raman spectra of one of the most important ferroelectrics to date -that is Pb(Zr,Ti)O 3 (PZT) -originates from a dynamical coupling between FE and AFD motions.…”

“…(1) to demonstrate that it is possible to develop such a scheme; (2) to apply it to PZT to prove its accuracy; (3) to gain a deeper knowledge into the additional peak that has been reported in Refs [12,13] (and that, as we found, does indeed originate from the coupling between FE and AFD motions); (4) to further use the proposed technique to reveal an electric-field-induced anticrossing involving FE and AFD degrees of freedom in PZT.…”