Changes In Vibrational Properties Research Articles

Infrared and Optical Properties of β‘-(ET)2SF5CF2SO3: Evidence for a 45 K Spin-Peierls Transition

We measured the polarized infrared reflectance of β‘-(ET)2SF5CF2SO3 as a function of temperature and analyzed the spin-exchange interactions of this salt by calculating the spin−orbital interaction energies between adjacent spin sites. The observed changes in vibrational properties below the 45 K transition support a weak lattice distortion in combination with a spin gap in this material. The spin-exchange interaction is predicted to occur primarily along the (−a +b) diagonal direction, in good agreement with the spectral data. In addition, notable frequency shifts of vibrational modes point to a second transition between 100 and 200 K. The low-lying electronic excitation in the stack direction (assigned as a charge-transfer feature based upon our electronic band structure calculations) shows distinct changes with temperature that are consistent with trends in the vibrational spectrum. The pattern of a high-temperature transition preceding the spin-Peierls transition is discussed in relation to other low-dimensional organic and inorganic materials.

Vibrational property changes of spruce wood by impregnation with water-soluble extractives of pernambuco (Guilandina echinata Spreng.)

Sitka spruce (Picea sitchensis Carr.) was treated with water-soluble extractive components of pernambuco (Guilandina echinata Spreng. syn Caesalpinia echinata Lam.) by two methods: impregnation under evacuation using an aspirator and repetitive surface application using a brush. The influence of these treatments on the vibrational properties were examined. The loss tangent (tan δ) of the impregnated specimen decreased, up to nearly a half of its original value, with increasing weight gain. It is suggested that the decrease in tan δ results from impregnation of the extractive components into the amorphous region of cell walls, forming secondary bonds between matrix substances. The surface application of the extractive components, on the other hand, hardly brought about the desirable change in vibrational properties.

Local environment effects in the vibrational properties of disordered alloys: An embedded-atom method study of Ni3Al and Cu3Au

Local environment effects are important for providing a framework for understanding the changes in vibrational properties that result from disordering. In the present work the effects of local environments on thermodynamic quantities are examined using the embedded-atom method (EAM) for Ni3Al and Cu3Au. Projections of the density of states onto different local environments are performed, and a local cluster expansion is calculated. It is found that the contribution to the entropy from a given atom is primarily determined by the atom and its first few neighbor shells. Relaxations are seen to qualitatively change the dependence of the entropy on local environment, changing the sign of the dominant interactions. Also, relaxations are found to extend the range of point and pair interactions and to increase the importance of multisite interactions. These results suggest that a special quasi-random structure (SQS), a small supercell constructed to approximate the local environments of the disordered phase, might be able to reproduce the disordered phase vibrational thermodynamics. It is found that an eight-atom SQS can accurately represent the vibrational thermodynamic properties of the disordered phase, implying that it could be a powerful tool for firstprinciples vibrational studies.