Xu Da-Peng

Preparation and Raman Spectrum of Rutile Single Crystals Using Floating Zone Method

With anatase-type titanium dioxide as the raw materials, the rutile type titanium dioxide single crystal is prepared using the floating zone method. The results of XRD measurements show that the grown crystal is highly crystalline with a rutile structure, which has orientation to the c-axis. The four Raman vibration characteristic peaks (143, 240, 450 and 610 cm(-1)) at room temperature show that the crystalline structure of the single crystal is a typical rutile phase, meanwhile a new Raman peak at around 690 cm(-1) is found. The results of the Raman measurement at various temperatures for the single crystal show that the Raman frequency shifts are different.

Raman Active Phonons in RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) Perovskites

We examine RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO3 perovskites crystallized in cubic symmetry for RCoO3 (R=La, Ce, Pr and Nd) and orthorhombic symmetry for RCoO3 (R=Sm, Eu, Gd, and Dy). It is found that the Raman spectra of RCoO3 perovskites are strongly dependent on the ionic radius of the rare earth elements, and the frequency shift of the most intense modes of the orthorhombic samples are correlated with some structural parameters such as Co-O bond distances, ionic radius of the rare earth elements and Jahn-Teller distortion. It is clear that Raman spectroscopy has the advantage of sensitivity to structure distortion and oxygen motion.

Raman shift of RMnO3 (R = La, Pr, Nd, Sm) manganites

Raman-active phonons in orthorhombic perovskite-like RMnO3 were studied by measuring Raman spectra in various scattering configurations. The experimental Raman line wave numbers and the expected shapes for the phonon modes were compared to those reported for other perovskite-like compounds with the Pnma structure and to the results of lattice dynamical calculations. The observed Raman lines in the spectra of RMnO3 were assigned to definite atomic motions. The remaining spectral weight can be explained by the presence of dynamic John-Teller distortions that lower the symmetry of the cubic perovskite.

Solid-state synthesis and properties of SmCoO3

In this paper, perovskite oxide SmCoO3 was prepared by the solid-state reaction method using Co2O3 and Sm2O3 as raw materials. The structure and properties of the samples were investigated by XRD, Raman spectral techniques, and DC measurements and so on. The results of XRD and Raman spectra showed that the mixtures of Co2O3 and Sm2O3 can react to produce a single phase perovskite oxide SmCoO3 around 1353 K. The single-phase SmCoO3 changes from an insulator to a semi-conductor and transition occurs around 470 K. The thermal expansion coefficient (2.17 × 10−5 K−1) of the single-phase SmCoO3 is approximately equal to that of doped LaGaO3, but much bigger than that of SDC(Ce0.85Sm0.15O2) above 873 K.

Phase Transition in CCl4 under Pressure: a Raman Spectroscopic Study

High-pressure Raman studies at room temperature are performed on CCl4 up to 13 GPa. The Raman bands of the internal modes (v2, v4 and v1) show entirely positive pressure dependence. The slopes dω/dP of the internal modes exhibit two sudden changes at 0.73 GPa and 7.13 GPa, respectively. A new lower frequency mode (225 cm−1) appears at 3.03 GPa, and the splitting of v2, v3 and v4 occurs at about 7.13 GPa. Moreover, Raman spectra of Fermi resonance show that the relative position of the v1 + v4 combination and the v3 fundamental firstly interchanges corresponding to that at ambient pressure, then the v1 + v4 combination disappears in the gradual process of compression. It is indicated that the pressure-induced phase transition from CCl4 II to CCl4 III occurs at 0.73 GPa, and CCl4 III undergoes a transition to CCl4 IV below 3.03 GPa. Further CCl4 IV transforms in a new high-pressure phase at about 7.13 GPa, and the symmetry of the new high-pressure phase is lower than that of CCl4 IV. All the transitions are reversible during decompression.

The investigation on the pressure-induced phase transition in linoleic acid by in situ Raman spectroscopy

With diamond anvil cell as a high-pressure apparatus, the in situ Raman spectra of linoleic acid from normal pressure to 1.29 GPa were measured to investigate the effect of pressure on the structural changes. In the pressure ranges of 0.07-0.12 GPa and 0.31-0.53 GPa, the significant changes in Raman spectra show that linoleic acid undergoes two pressure-induced phase transitions. Spectral analysis indicates that the polymethylene chain of linoleic acid molecule transforms from the disordered gauche conformation to the ordered trans conformation in the range of 0.07-0.12 GPa. And the polymethylene chain of linoleic acid molecule remains the ordered trans conformation whereas the conformation of the olefin group significantly changes and the degree of conformational order increases in the range of 0.31-0.53 GPa. The pressure-induced phase transitions in linoleic acid are reversible.

Zinc oxide hexagram microrods

Zinc oxide (ZnO) microrods were grown by the floating zone method, the as-grown ZnO microrods have uniform size. Scanning electron microscope image reveals that the ZnO microrods are grown with a hexagonal structure, well faceted ends and side surfaces. Most of ZnO microrods have diameters of about 20–30nm and lengths of about 1–2 mm. Polarizing microscopy image of ZnO microrods shows that they have high crystal quality. The X-Ray diffraction pattern shows that microrods have vertical orientation. The Raman spectra demonstrate that the vibrational mode of wurtzite-type ZnO clearly. The room temperature photoluminescence measurements indicate that the microrods have a relative strong ultraviolet (UV) emission and very weak green emission.

The formation and stability of quasicrystal in Al80Mn14Si6 under high static pressure

Abstract The method of quenching in fusing state under high static pressure (MQFSHP) was applied for the first time to prepare the quasicrystal icosahedral phase of Al80Mn14Si6 alloy. The pressure was from 2.8GPa to 3.1GPa and the cooling rate during quenching was of about 100°C/s. Some sharp electron diffraction spots showing an arrangement with a five-fold symmetry axis and noncrystalline ring have been observed in electron diffraction experiment. The crystallization temperature of I phase obtained from high pressure(HP) is close to that of rapid cooling ribbon, but the cooling rate of the sample obtained is lower than that of rapid cooling ribbon.