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The structural and dielectric properties of both pure and Nd(super 3+)-doped Ba(sub 0.77)Ca(sub 0.23)TiO(sub 3) ceramics obtained from solid-state reaction are investigated. Raman scattering measurements and the dielectric constant indicate that the Curie temperature of the ferroelectric phase transition depends on Nd(super 3+) content.

The n, m indices determination of individual nanotubes can be accomplished by the resonant Raman specta from a single wall carbon nanotube. The method also enables corroboration of the n, m assignment by diameter- and chirality- dependent phenomena in Raman modes consisting of G-band, D-band, and G'-band features.

Abstract: The structural and electronic charge distributions of single-wall carbon nanotubes (SWNTs) chemically modified with Ag and CrO3 were investigated by ab initio methods. Using first-principles spin-polarized calculations, we studied the structural and electronic behavior of Ag atoms and CrO3 molecules interacting with an (8,0) semiconducting SWNT. We have found that the Ag atom behaves as an electron donor and the CrO3 as an electron acceptor in the presence of the SWNT. Resonance Raman experiments performed on Ag and CrO3-adsorbed SWNTs confirm the donor and acceptor behavior, respectively. [Copyright &y& Elsevier]

In this work we present a Raman study of PbZr 1-x Ti x O 3 ceramics with composition values close to the morphotropic phase boundary region. The analysis of the Raman spectra leads to the determination of the monoclinic phase extension at different temperatures in a very good agreement with those determined by diffraction techniques. Therefore the obtained results show that Raman spectroscopy is a powerful and suitable technique to study structural phase transitions in PbZr 1-x Ti x O 3 . [ABSTRACT FROM AUTHOR]

Raman spectra of (3C-SiC)[sub 8-δ]/(3C-SiC[sub 0.5]Si[sub 0.5])[sub δ]/(Si)[sub 8-δ]/(3C-SiC[sub 0.5]Si[sub 0.5])[sub δ] superlattices with interfacial transition regions of thickness δ varying from one to three monolayers are calculated. It is shown that severe frequency shifts (up to -86 cm[sup -1]) and the flattening of the folded optical phonons dispersion curves are due to the interfacial regions, strongly affecting the Raman spectrum in consequence. With increasing interface thickness, the Raman peaks are enhanced in the middle frequency range. These effects are mainly attributed to localization of atomic displacements at the Si/3C-SiC or the 3C-SiC/Si interfacial transition regions. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Polarized Raman spectra and polycrystalline spectra of isomorphous Sc2(MoO4)3 and Al2(WO4)3 crystals have been measured at room temperature and ambient pressure. Some Raman spectra of Sc2(MoO4)3 were taken at different values of pressures in the range of 0.0–3.0GPa. Lattice dynamics calculations have been performed on the orthorhombic phase (ambient phase) of these materials using a rigid ion model in order to calculate the phonon frequencies at the Brillouin zone Center (k =0). The calculated results fit qualitatively well the Raman spectra observed in these materials at room temperature and ambient pressure, and allowed us to establish their Raman signature. A higher coupling among the modes of the Al2(WO4)3 material compared with Sc2(MoO4)3 material was observed. The pressure dependent studies revealed that the 362 and 433cm−1 modes of Sc2(MoO4)3 and Al2(WO4)3, respectively, exhibit unusually high ∂ω/∂P values. The presence of these unstable modes in both materials is probably related to the mechanism of the phase transition from the monoclinic high-pressure phase to the unknown phase of lower symmetry. [Copyright &y& Elsevier]

Abstract: We have measured Raman and infrared spectra of α-Ge(HPO4)2·H2O compound at room temperature. The analysis of vibrational modes indicated the presence of two non-equivalent HPO4 2− units in agreement with 31P nuclear magnetic resonance measurements. A tentative assignment of all the observed modes is proposed based on the previous works reported for other hydrogenphosphate-based compounds. [Copyright &y& Elsevier]

Abstract: In this work, X-ray diffraction, Raman spectroscopy and differential scanning calorimetry techniques were used to understand the crystallization process on 20Li2O–80TeO2 glass. X-ray diffraction results reveal the presence of three distinct alpha γ-TeO2, α-TeO2 and α-Li2Te2O5 crystalline phases in the glass matrix. The Raman spectroscopy band structure of this glass is similar to the one observed in glassy TeO2. Raman results clearly reveal the metastable character of the γ-TeO2 phase in the 20Li2O–80TeO2 glass, whose associated vibration modes disappear completely at temperatures higher than 315°C. On the other hand, the Raman modes associated to α-TeO2 and α-Li2Te2O5 phases persists up to temperatures close to the final stages of the crystallization in the studied glass (around 420°C). From DSC measurements, the activation energies 296±3 and 298±1kJmol−1 were associated to γ-TeO2 and α-TeO2 phases crystallization, indicating that these phases crystallizes at temperatures very close in the studied glass. [Copyright &y& Elsevier]