The experimental approach combining high resolution transmission electron microscopy (HRTEM), electron diffraction (ED) and resonant Raman spectroscopy (RRS) on the same freestanding individual carbon nanotubes (CNT) is the most efficient method to determine unambiguously the intrinsic features of the Raman-active phonons. In this paper, we review the main results obtained by the approach regarding the intrinsic features of the phonons of singlewalled (SWNT) and double-walled carbon nanotubes (DWNT). First, we detail the different methods to identify the structure of SWNTs and DWNTs from the analysis of their electron diffraction patterns (EDP). In the following, we remind the principal features of the Raman response of SWNTs, unambiguously index-identified by ED. A special attention is devoted to the effect of the inter-layer interaction on the frequencies of the Raman-active phonons in indexidentified DWNTs. The information obtained on index-identified SWNT and DWNT allows us to propose Raman criteria, which help identifying CNT when the ED fails to propose a single assignment. The efficiency of the Raman criteria as the complement to the ED information for the index-assignment of a few SWNTs and DWNTs is shown. The same approach to index-assign a triple-walled carbon nanotube (TWNT), by combining ED and RRS information, is reported.
Raman scattering experiments were performed on the relaxor ferroelectric lead magnesio-niobate (PMN), the ferroelectric 0.8 PMN-0.2 (PT) and the intermediate composition 0.9 PMN-0.1 PT. In order to understand in more detail the behaviour of this series, Raman scattering spectra were also collected under dc electric field. A ferroelectric phase could be induced in the latter composition for electric fields higher than a threshold value. The behaviour of this field-induced phase was compared with the (zero-field) ferroelectric phase in 0.8 PMN-0.2 PT. Barkhausen jumps were observed in the pyroelectric current measurements, and a strong dielectric anomaly was detected in zero field heating after field cooling experiments on 0.9 PMN-0.1 PT. These results are consistent with a description of the behaviour in this series based on a cancellation of 1:1 (Mg:Nb) domain random fields by titanium ions, favouring the onset of long range ferroelectric order.
A Raman study of a highly oriented PbTiO3 thin film deposited on a MgO single crystal has been performed as a function of the temperature. The results have been compared with those obtained from a single crystal prepared from the same batch and those reported in the literature for polycrystalline thin films and single crystals. A shift in the transition temperature is observed from the soft mode behavior, together with more usual lower values of its frequency, which are both related to effective hydrostatic pressure due to the clamping of grains by their neighbors in the distorted tetragonal structure. The large soft mode linewidth and its integrated intensity, which do not vanish at the ferroelectric to paraelectric transition temperature, have been interpreted in terms of the coupling of this mode (and more generally of all polar phonons) with the static strain fields originating from the clamping effect and the epitaxial conditions.
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