Single wall carbon nanotubes (SWNTs) that are found as close-packed arrays in crystalline ropes have been studied by using Raman scattering techniques with laser excitation wavelengths in the range from 514.5 to 1320 nanometers. Numerous Raman peaks were observed and identified with vibrational modes of armchair symmetry (n, n) SWNTs. The Raman spectra are in good agreement with lattice dynamics calculations based on C-C force constants used to fit the two-dimensional, experimental phonon dispersion of a single graphene sheet. Calculated intensities from a nonresonant, bond polarizability model optimized for sp2 carbon are also in qualitative agreement with the Raman data, although a resonant Raman scattering process is also taking place. This resonance results from the one-dimensional quantum confinement of the electrons in the nanotube.

https://science.sciencemag.org/content/sci/275/5297/187.full.pdf

Diameter-Selective Raman Scattering from Vibrational Modes in Carbon Nanotubes

Vibrational modes of carbon nanotubes; Spectroscopy and theory

The pressure-temperature phase and transformation diagram for carbon; updated through 1994

Borate glasses are the technologically important class of glasses and play a significant role in various applications. Borate glasses contain planar BO3 groups as structural units, rather than tetrahedral SiO4 groups. The oxygen atoms are, as in SiO2, again connected to two network-forming atoms, in case of boron. The radial distribution analysis describes the B2O3 glass structure as consisting of boroxol rings, that is, planar rings containing three boron atoms and three oxygen atoms. The network forming of the B2O3 and the SiO4 is affected with the addition of some metal cation additives Pb, Zn, Cd, and so forth. These additives also work as a network modifier and a nucleating agent for crystallization of glass. Therefore, the optical properties of the borate glasses have been changed significantly.

https://downloads.hindawi.com/archive/2012/428497.pdf

A Review on Infrared Spectroscopy of Borate Glasses with Effects of Different Additives

Pressure induced amorphization of materials

Glasses in the system $xPbO:(100- x)B_2O_3 (22\leq x\leq 85$ mol%) have been studied by Raman spectroscopy with a view to understand the effect of PbO on the borate network. The conversion of three-fold to four-fold coordinated boron takes place primanly by incorporation of $BO_4$ into boroxol rings in the form of pentaborate and diborate units. For high lead content, back conversmn of four to three coordinatmn of borons occurs and the network consists primardy of pyroborate, orthoborate and metaborate groups.

Raman study of lead borate glasses

Raman experiments have been carried out on single crystals of ${\mathrm{BaTiO}}_{3}$ as a function of pressure up to 3.5 GPa across the ferroelectric (tetragonal) to paraelectric (cubic) phase transition. The unusual features in the Raman spectra associated with the interference effects due to coupling of the three ${\mathit{A}}_{1}$(TO) phonons are studied quantitatively to obtain the pressure dependence of the line shape parameters and the coupling constants. The frequencies of the middle and highest-frequency modes as well as the linewidth of the middle mode show interesting pressure dependence.

Phonon interference in BaTiO3: High-pressure Raman study.

High pressure phase transition in metallic LaB6: Raman and X-ray diffraction studies

We have studied single crystals of C70 by Raman scattering and photoluminescence in the pressure range from 0 to 3 1.1 GPa. The Raman spectrum at 3 1.1 GPa shows only a broadband similar to that of the amorphous carbon without any trace of the Raman lines of CT0. After releasing the pressure from 3 1.1 GPa, the Raman and the photoluminescence spectra of the recovered sample are that of the starting C70 crystal. These results indicate that the C70 molecules are stable up to 3 1.1 GPa and the amorphous carbon high pressure phase is reversible, in sharp contrast to the results on solid Cm. A qualitative explanation is suggested in terms of intermolecular versus intramolecular interactions.

https://arxiv.org/pdf/cond-mat/9411120.pdf

N. Chandrabhas

Papers

Raman study of lead borate glasses

Phonon interference in BaTiO3: High-pressure Raman study.

High pressure phase transition in metallic LaB6: Raman and X-ray diffraction studies

Reversible pressure-induced amorphization in solid C70: Raman and photoluminescence study.

Pressure-induced orientational ordering in C60 crystals as revealed by Raman spectroscopy