Temperature Dependence Of Vibrational Modes Research Articles

Phonon anharmonicity in bulk ZrTe5

AbstractThe study of phonon scattering processes is urgent for advancing the thermoelectric material with low thermal conductivity for commercial application. In this work, Raman scattering spectroscopy is utilized to quantify the temperature dependence of vibrational modes in ZrTe5 crystals, which enables the investigation on anharmonic contributions. We mainly focus on the temperature range from 80 up to 400 K due to noticeable surface oxidation at higher temperature. The phonon behaviors can be fully described by the model considering two mechanisms of the lattice thermal expansion effects and intrinsic anharmonicity. The four‐phonon processes are non‐negligible and even stronger than the three‐phonon processes at high temperature. The phonon lifetime is greatly reduced by the enhancement of phonon scattering, contributing to the low thermal conductivity in ZrTe5 single crystals.

Order-disorder phase transition in the peroxidovanadium complex NH4[VO(O2)2(NH3)

Complex NH4[VO(O2)2(NH3)] (1) undergoes an order-disorder phase transition at Tc~258K. This transition is accompanied by change in the space group of the orthorhombic lattice and also by significant structural rearrangements of the constituent molecules, which are pertinent mostly to their NH4+ ions and their ammonia ligands. The low-temperature solid state IR and Raman spectra of 1 were corroborated by solid-state computations that employed Gaussian functions as the basis set. Results of these computations yielded excellent agreement with experimental data. On the curves of temperature dependence of vibrational modes, the phase transition is expressed by an abrupt change of the slope above Tc.

Temperature dependence of vibrational modes of CH3CC(ads) and I(ads) coadsorbed on Ag(111): Ab initio molecular dynamics approach

Ab initio molecular dynamics simulations accompanied by a Fourier transform of the dipole moment (aligned perpendicular to the surface) autocorrelation function are implemented to investigate the temperature-dependent infrared (IR) active vibrational modes of CH3C(β)C(α)(ads) and I(ads) when coadsorbed on an Ag(111) surface at 200 and 400 K, respectively. The analytic scheme of the Fourier transform of a structural coordinate autocorrelation function is used to identify two distinguishable IR active peaks of C(β)C(α) stretching, which are characterized by two types of dynamic motion of adsorbed CH3C(β)C(α)(ads) at 200 K, namely, the motion of the tilted CC(β)C(α) axis and the motion of the stand-up CC(β)C(α) axis. These two recognisable IR active peaks of C(β)C(α) stretching are gradually merged into one peak as a result of the dominant motion of the stand-up CC(β)C(α) axis as the temperature increases from 200 to 400 K. The calculated intensities of the IR active peaks of the asymmetrical deformation mode of CH3 and the asymmetrical stretching mode of CH3, with their dynamic dipole moments nearly perpendicular to the CC(β)C(α) axis, become relatively weak; however, the symmetrical deformation mode of CH3 and the symmetrical stretching mode of CH3, with their dynamic dipole moments randomly directed away from the CC(β)C(α) axis, will not have direct correspondence between the intensities of their IR active peaks and the angle between the Ag(111) surface and the CC(β)C(α) axis as the temperature increases from 200 to 400 K. Finally, the increased flipping from the motion of the tilted CC(β)C(α) axis to the motion of the stand-up CC(β)C(α) axis followed by its diffusion, resulting from the increasing temperature from 200 to 400 K or even higher, seems to be the initial event that initiates the alkyne self-coupling reaction that leads to the final production of H3CCCCCCH3.

Lattice dynamics calculations and temperature dependence of vibrational modes of ferroelasticLi2TiGeO5

Raman and polycrystalline IR spectra were obtained forLi2TiGeO5 and the assignment of the observed bands to the respective internal and external phononshas been proposed on the basis of lattice dynamics calculations. Temperature dependencesof Raman- and IR-active phonons are also reported to probe the paraelastic–ferroelasticphase transition that takes place at 233.5 K. This study shows that the phase transition iscontinuous and that this phase transition leads to significant distortion of the unit cell.

Vibrational Study of Phase Transitions in KIn(WO4)2

Studies of the low-temperature D162h orthorhombic phase and investigation of trigonal–monoclinic phase transition in quenched high-temperature phase KIn(WO4)2 were performed by means of infrared and Raman spectroscopy. The observed vibrational modes were assigned to the vibrations of respective atoms in the unit cells. It has been shown that as a result of the trigonal–monoclinic phase transition a similar temperature dependence of vibrational modes has been observed as that found for KSc(WO4)2 although crystallographic studies suggest that the former crystal has D43d and the later D33d structure.

Temperature-dependent Raman spectra of ferroelectric potassium strontium niobate

The temperature dependence of vibrational modes polarized parallel to the polar axis of potassium strontium niobate, a 'tungsten-bronze'-type ferroelectric, is investigated using polarized Raman techniques. The low-frequency Rayleigh component of the spectrum may be fitted to a Debye relaxation spectral function, the relaxation time appearing to increase towards the ferroelectric-paraelectric phase transition as is observed in some hydrogen-bonded ferroelectrics. Dielectric dispersion measurements are presented which are consistent with a Debye relaxation over a comparable frequency regime. Measurements of the integrated intensity of the A1 (TO) modes as a function of temperature are discussed in terms of the static dielectric properties of the material.