P.T.C. Freire

Raman study of morphotropic phase boundary in PbZr 1 − x Ti x O 3 at low temperatures

The Raman spectra of

Pressure-induced phase transitions in monohydrated l-asparagine aminoacid crystals

{\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}

Polarized Raman Spectra and Infrared Analysis of Vibrational Modes in L-Threonine Crystals

ceramics with titanium concentration varying between

Monoclinic phase ofPbZr0.52Ti0.48O3ceramics: Raman and phenomenological thermodynamic studies

x=0.40

High temperature Raman spectra of L-leucine crystals

and 0.60 were measured at 7 K. By observing the concentration-frequency dependence of the vibrational modes, we identified the boundaries among the rhombohedral, monoclinic, and tetragonal ferroelectric phases. The analysis of the spectra was made in the view of group theory analysis making possible the assignment of some modes for the monoclinic phase.

Raman scattering studies of monohydrated L-asparagine

Abstract Single-crystal samples of monohydrated l-asparagine, C4N2O3H8. H2O, a fundamental aminoacid of the human body and other complex beings, have been studied by Raman spectroscopy in a diamond-anvil cell up to pressures of 2.0 GPa. From the analysis of results we observed that the crystal undergoes a series of three phase transitions. All transitions are accompanied by drastic changes in the external modes and in some internal modes of the crystal, which shows in a clear way the transitions induced by the hydrostatic pressure. Pressure coefficients for external modes are also given.

Structural and dielectric properties of Nd3+-doped Ba0.77Ca0.23TiO3 ceramics

Polarized Raman and infrared espectra of l-threonine crystals have been obtained at room temperature and an assignment of normal modes is proposed based on group theory analysis. The usefulness of these assignments comes from the fact that some modes are related to important vibrations that can show changes under different pressure and temperature conditions.

High‐pressure Raman study of taurine crystal

This work reports on the first Raman detection of the tetragonal to monoclinic phase transition in PZT ceramics near morphotropic phase boundary at low temperatures. The transition is characterized by changes in the frequency of lattice modes with the temperature. The results presented here confirm the previous one recently reported by Noheda et al. using high-resolution synchrotron X-ray powder diffraction technique and dielectric measurements. The stability of the new phase is discussed within the framework of phenomenological Landau-Devonshire Theory.

Raman scattering study of NaAl(MoO4)2 crystal under high pressures

Single crystal samples of L-leucine, C6H13NO2, a fundamental aliphatic amino acid of the human body, have been studied by Raman spectroscopy at temperatures from 300 to 430 K over the spectral range from 50 to 3100 cm -1. A tentative assignment of all bands is given. For high temperatures, several modifications on the Raman spectra were observed at about 353 K, giving evidence that the L-leucine crystal undergoes a structural phase transition. An interpretation for this phase transition in terms of group theory analysis is given.

Pressure-induced phase transitions in ferroelectric Bi2MoO6—a Raman scattering study

Polarized first-order Raman scattering studies at 300 K were carried out in L-asparagine monohydrate crystal in order to obtain the general assignment of its phonon spectra. A careful analysis of the vibrational spectra shows that the assignment of the fundamental vibrational modes can be done on the basis of amino, carboxilic and water groups vibrations, and correlations with previous data reported for other amino acids. However, some vibrations were correctly assigned from the study of its temperature - dependence behavior performed in the range 10 - 300 K. The assignment proposed cofirm the zwitterionic structure of L-asparagine monohydrate crystal.