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The dielectric behavior of (Pb1-x/2Lax)(Zr0.9Ti0.1)O3 PLZT 100x/90/10 (0≤100x≤1) was studied in the frequency range 102-1014 Hz using dielectric, time-domain terahertz (THz), far-infrared, and Raman spectroscopy in the temperature interval 10-900 K. PZT 90/10 and PLZT 2/90/10 undergo two phase transitions, from a cubic paraelectric to a rhombohedral untilted ferroelectric (FE) phase and on further cooling to a tilted FE phase. PLZT 4/90/10 and PLZT 10/90/10 are incommensurately modulated and composed of an intergrowth of polar and antipolar cation displacements. These samples consequently demonstrate a FE soft mode which exhibits minimal frequency several tens of degrees above the nominal antiferroelectric phase transition temperature. The dielectric response of PLZT 100x/90/10 is mainly governed by a gigahertz relaxation and a soft phonon component in the THz range. As in other PbO-based perovskites, the soft mode is split into a higher-frequency component (ω∼80 cm-1) and a highly damped THz component (ω∼30 cm-1), with larger dielectric strength already in the paraelectric phase. [ABSTRACT FROM AUTHOR]

The paper describes investigation of the electric-field-induced phase transition in PMN-xPT single crystals withx= 0.32 by means of detailed polarized Raman scattering measurements. Field-induced tetragonal state was reached by applying an electric field up to 30 kV/cm along pseudo-cubic direction at a temperature slightly below that of the zero-field rhombohedral–tetragonal phase transition (TRT). In this field-induced tetragonal state, the angular dependencies of the polarized Raman spectra were recorded and compared with the similar data available for the rhombohedral single-domain and multidomain states. [ABSTRACT FROM AUTHOR]

A comparative analysis of Raman spectra from poly-domain PbTiO3 thin films with poly-domain and single-domain PbTiO3 crystals is presented. Raman spectroscopy reveals that the profiles of A1-symmetry modes can be significantly modified by the existence of the domain structure. The possible origins of these complex profiles of the A1(LO) and A1(TO) modes are discussed. It is emphasized that analysis of stresses, domain structure and phase transitions in the PbTiO3 thin films has to be based on the E(TO) modes presenting profiles that are not affected by the domain structure. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate ceramics Pb(Zr1-xTix)O3 with spatially graded composition from X = 46 to 49 were studied by Raman scanning microscopy and the results were compared with Raman spectra in PZT ceramics of different compositions around the morphotropic phase boundary (MPB). An E-symmetry mode located near 200 cm-1 was found to be a measure of the tetragonality of PZT in both standard graded ceramics. The singular value decomposition method was applied to decompose the experimental spectra of the graded ceramics. Two main contributions were found: one is related to the intensity of the main transverse modes - especially the E(TO2) mode - and it gives evidence of the change between tetragonal and rhombohedral symmetries in the sample; the second one shows changes just through the spatial MPB and it is related to the intensities of A1(TO2) and E(LO2) modes. All the phonons involved in the main changes correspond to Zr and Ti vibrations. [ABSTRACT FROM AUTHOR]

In this study, ceramic samples of lead zirconate titanate Pb(Zr0.42Ti0.58)O3 (PZT 42/58) doped with Fe (hard) and Nb (soft) were studied by Raman, infrared (IR) and THz spectroscopy in the temperature range from 900 to 20 K. From the evaluation of the IR and Raman phonons in undoped ceramics, we conclude that tetragonal PZT ceramics undergo a low-temperature phase transition to a tilted phase, revealed by anomalies in phonon parameters and the appearance of new modes. Doped samples also presented similar behaviour. The main differences between undoped and doped ceramics lie in the dielectric behaviour below phonon frequency range, where several mechanisms appear: a soft central mode (CM) located near 1 THz and two relaxations in the GHz range. Both types of doping raise the permittivity values below the phonon frequencies, not only increasing the dielectric contribution of the CM, but also modifying the dielectric response near the GHz range. Soft ceramics show higher permittivity with logarithmic increase at low frequencies, corresponding to an almost frequency-independent value of the dielectric losses below 0.1 GHz. [ABSTRACT FROM AUTHOR]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]

The lattice dynamics of Pb1-xLax(Zr0.9Ti0.1)O3 (PLZT X/90/10) with X=0, 2, 4, 10% of La was studied by means of Far Infrared, Raman and terahertz spectroscopies in the temperature range of 20–800 K. Infrared active soft phonons with anomalies near the paraelectric-ferroelectric phase transition were found for all the samples. Some Raman active phonons show anomalies ∼200 K below TC, due to another phase transition to a ferroelectric state with doubled unit cell. Samples with higher La content (X=4,10) display nonclassical phonon softening described by ω2=a(T-TC)γ with γ=2/3. [ABSTRACT FROM AUTHOR]

The dielectric behavior of (Pb1-x/2Lax)(Zr0.9Ti0.1)O3 PLZT 100x/90/10 (0≤100x≤1) was studied in the frequency range 102-1014 Hz using dielectric, time-domain terahertz (THz), far-infrared, and Raman spectroscopy in the temperature interval 10-900 K. PZT 90/10 and PLZT 2/90/10 undergo two phase transitions, from a cubic paraelectric to a rhombohedral untilted ferroelectric (FE) phase and on further cooling to a tilted FE phase. PLZT 4/90/10 and PLZT 10/90/10 are incommensurately modulated and composed of an intergrowth of polar and antipolar cation displacements. These samples consequently demonstrate a FE soft mode which exhibits minimal frequency several tens of degrees above the nominal antiferroelectric phase transition temperature. The dielectric response of PLZT 100x/90/10 is mainly governed by a gigahertz relaxation and a soft phonon component in the THz range. As in other PbO-based perovskites, the soft mode is split into a higher-frequency component (ω∼80 cm-1) and a highly damped THz component (ω∼30 cm-1), with larger dielectric strength already in the paraelectric phase. [ABSTRACT FROM AUTHOR]

Hyper-Raman scattering experiments allowed collecting the spectra of the lowest F1u-symmetry mode of PbTiO3 crystal in the paraelectric phase up to ≈930 K as well as down to about 1 K above the phase transition. It is realized that this mode is fully responsible for the Curie-Weiss behavior of its dielectric permittivity above Tc. Near the phase transition, this phonon frequency softens down to 17 cm-1 and its spectrum can be well modeled as a response of a single damped harmonic oscillator. It is concluded that PbTiO3 constitutes a clean example of a soft-mode-driven ferroelectric system. [ABSTRACT FROM AUTHOR]

Abstract: Inelastic light scattering is used to study lattice dynamics of strontium titanate (STO) ceramics with several heterovalent dopants (La3+, Gd3+, Y3+), which substitute Sr2+ ions. An extraordinary shift of the antiferrodistortive transition temperature (T a) is ascertained when just a small percentage of any of the dopants is used. T a is dependent on the tolerance factor (t). In this work, it is clearly shown that, regardless of the dopant used, a common linear dependence of T a vs. t is obtained if strontium vacancies are taken into account. A vacancy size of ∼1.547Å was estimated, which is ∼7% larger than the Sr2+ radius. The vacancy size obtained can directly explain the increase in lattice parameter with increasing Bi3+ content in Bi-doped STO, as opposed to the dopants referred to above. Furthermore, the introduction of La3+, Gd3+ or Y3+ ions at the Sr site causes a considerable stiffening of the transverse optic TO1 mode at low temperatures, thereby decreasing the phonon contribution to the dielectric permittivity. Thus, no traces of a ferroelectric phase are found for any of the dopants used in this work. [Copyright &y& Elsevier]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]