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E-symmetry optical phonons at the Γ point of LiNbO3 and LiTaO3 were experimentally resolved in spectra measured by infrared and Raman spectroscopy. For this purpose, congruent and nearly stoichiometric crystals of LiNbO3 and LiTaO3, and mixed LiNb1-xTaxO3, crystals were studied. The results show that some of the E modes have weak intensities in Raman or infrared spectra. Thus the complete assignment of E-symmetry modes has been achieved by comparing Raman and infrared data. In addition, this assignment has been confirmed by Raman measurements at low temperatures. [ABSTRACT FROM AUTHOR]

The paper describes experiments revealing the anisotropy of the macroscopic dielectric response of poled lead zirconate titanate ceramics in the phonon frequency region. The results are discussed in terms of distinct polar phonon contributions and effective medium theory. The anisotropy probed in far-infrared experiments can be used to evaluate efficiency of the poling and/or depoling processes. [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]

Phonons in K0.5Na0.5NbO3 (KNN-50) ceramics were investigated from 10 to 900 K by means of Raman, infrared and THz spectroscopy. A first-order phase transition was detected from cubic to tetragonal phases at about 710 K, when the first component of the polarization appears. Transition from the tetragonal to the orthorhombic phase takes place around 475 K. The last transition from orthorhombic to rhombohedral phases is strongly first order. TC is about 90 K in KNN-50. All Raman active modes below 100 cm- 1 disappear. An overdamped soft mode present at high temperatures in the THz range changes its dielectric strength at each phase transition (when the corresponding component jumps to higher frequencies) and abruptly disappears in the rhombohedral phase. However another excitation at lower frequency than the phonons is needed to explain the static value of the permittivity. [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]

Intraband electronic excitations, phonons, and crystal field transitions of two unique (Nd,Eu,Gd)Ba 2 Cu 3 O y single crystals with different Eu/Gd ratio were studied by Raman spectroscopy. The spectra were measured above and below critical temperature. The phonon symmetries were determined from the angular dependence of the spectra. The line shapes of barium, planar oxygen, and apical oxygen ions’ vibrations were affected by interaction of the phonons with intraband electronic excitations. We fitted the spectra at all measured temperatures and disentangled the phonon contributions from those of the intraband electronic excitations and identified corresponding interference terms. Below T c , a broad, superconductivity-induced high-frequency peak appeared in the spectra of both crystals. Damping of the Raman active phonons in our crystals correlated well with varying pinning disorder in the crystals. [ABSTRACT FROM AUTHOR]

Polarized Raman, IR, and time-domain THz spectroscopy of orthorhombic lead zirconate single crystals have yielded a comprehensive picture of temperature-dependent quasiharmonic frequencies of its low-frequency phonon modes. It is argued that these modes primarily involve vibrations of Pb ions and librations of oxygen octahedra. Their relation to phonon modes of the parent cubic phase is proposed. Counts of the observed IR and Raman active modes belonging to distinct irreducible representations agree quite well with group-theory predictions. Analysis of the results yields insight into the phase transition mechanism, involving a soft ferroelectric branch coupled by a trilinear term to another two oxygen octahedra tilt modes. [ABSTRACT FROM AUTHOR]