Guoxiang Lan

Graphical method for assigning Raman peaks of radial breathing modes of single-wall carbon nanotubes

In order to assign Raman scattering peaks of radial breathing modes (RBMs) of single-wall carbon nanotubes (SWNTs), we have already developed a graphical method. Two charts were constructed based on the data of diameters, RBM frequencies and electronic density of states (DOS) of SWNTs. Using them we have successfully assigned resonant scattering peaks of RBM in the Raman Spectra recorded by Rao et al. The assignments indicate that SWNT samples exhibit many different structures with no one species dominating.

The effect of catalyst concentration on the synthesis of single-wall carbon nanotubes

Single wall carbon nanotubes (SWNTs) were synthesized by electric arc discharge method with a mixture of nickel and yttrium as catalysts. The effect of the catalyst concentration on the synthesis of SWNTs was studied. Raman spectra of SWNTs have been recorded with excitation wavelengths from 476.5 to 1064 nm. The Raman peaks of the radial breathing modes (RBM) of SWNTs were assigned. The results indicate that the diameter distribution of SWNTs is in the range of 1.2-1.6 nm, and the SWNTs with diameter 1.43 nm are in the majority. The catalyst concentrations have large effect on the yield of SWNTs and little effect on the diameter distribution of SWNTs.

Raman spectra of 3-methyl-4-nitropyridine-N-oxide single crystal

Abstract A Raman study of 3-methyl-4-nitropyridine-N-oxide single crystal (3M4NPO) has been performed at 78 K in the range 10–3500 cm−1. The symmetry analysis of the vibrational modes of 3M4NPO is given. The assignments are presented for internal and external modes. The results of the Raman spectra exhibit the spectroscopic proofs of hydrogen bonds in the crystal.

Family behaviour of Raman-active phonon frequencies of single-wall nanotubes of C, BN and BC3

Using a symmetry-based force-constant model of the lattice dynamics, the Raman-active phonon frequencies are calculated for almost 200 single-wall nanotubes of C, BN and BC(3). The n+m=constant family behaviour is found in most branches and these three kinds of nanotubes display different diameter and chirality dependence in different branches. In these branches, vibration modes that C, BN and BC(3) nanotubes have in common are presented in detail. For a particular family, the phonon frequency at Gamma point changes regularly with the chiral angle. Therefore, we may distinguish among single-wall nanotubes with similar diameter and different chiral angle.

Pressure-induced amorphization study of lithium diborate

Abstract High-pressure Raman spectra of lithium diborate (Li2B4O7) crystal are presented in this paper. The results show that lithium diborate becomes amorphous phase above 17.0 GPa. In the range of 17.0–30.3 GPa the transition is reversible and it is irreversible above 32.0 GPa. The structure of pressure-induced amorphous Li2B4O7 is different from that of glassy Li2B4O7. The recrystallization process of the pressure-induced amorphous state was investigated by means of Raman scattering. It shows that the recrystallized temperature of pressure-induced amorphous Li2B4O7 is about 700 °C.

Raman‐scattering study on pressure amorphization of LiNbO3 crystal

A high‐pressure Raman‐scattering study reveals that crystalline LiNbO2 becomes amorphous at about 31 GPa, and this transition is irreversible above 35.8 GPa. The spectrum of pressure‐ amorphized LiNbO3 is similar to that of glassy LiNbO3.

Vibrational spectroscopic study of (NH2CH2COOH)2CdCl2 crystal

Abstract The Raman and the infrared absorption spectra of diglycine cadmium chloride (NH 2 CH 2 COOH) 2 CdCl 2 crystal have been recorded. The observed vibrational bands are assigned to the internal vibrations of glycine molecules. The vibrational spectra show that the glycine molecule is in the form of the zwitterion in the crystal.

Vibrational spectra of lead tetraborate: experimental and theoretical analysis

Raman and infrared reflectance spectra of single-crystal lead tetraborate (PbB4O7:PTB) have been recorded. Using a first-principles calculation, the phonon dispersion relation of PTB has been derived within the local density approximation. A symmetry analysis of the phonon modes at the centre of Brillouin zone was performed, and calculated frequencies are compared to experimental spectra. A good agreement between calculated and measured frequencies was obtained.

Recrystallization and formation of pressure-amorphized Li2Ge7O15

A high-pressure Raman scattering study on Li2Ge7O15 up to 19 GPa reveals the occurrence of a phase transition from the crystalline to the amorphous state at 12.7 GPa. The amorphization is reversible below 15.5 GPa and irreversible above 15.5 GPa. This transformation occurs via polyhedral tilting. Crystallization processes of pressure-amorphized Li2Ge7O15 are also investigated by Raman scattering. An intermediate phase ( alpha -quartz form GeO2) is crystallized at 520 degrees C and the stable phase of Li2Ge7O15 is formed at 620 degrees C.

High-pressure Raman spectra of lithium triborate crystal and pressure-induced phase transitions

Abstract The high-pressure Raman spectra of lithium triborate (LiB 3 O 5 ) crystal are presented in this work. The results show that a pressure-induced crystalline-to-crystalline phase transition occurs near 50 kbar and that the phase transition is reversible. Above 270 kbar lithium triborate becomes amorphous; this transition is irreversible. The structure of pressure-amorphized LiB 3 O 5 and the recrystallization processes on annealing were investigated by means of Raman scattering.