Temperature Dependence Of Frequency Shift Research Articles

Temperature dependence of Raman-active mode frequencies and linewidths in TlGaSe2 layered crystals

Raman spectra of TlGaSe2 crystal at different temperatures are discussed. The temperature dependence of frequency shifts and linewidths of the Raman peaks in the frequency region of 10-320 cm-1 have been measured in the range from 50 to 320 K. The analysis of the experimental data showed that the temperature dependencies of phonon frequencies and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The anharmonic contribution (phonon-phonon coupling) is found to be due to three-phonon processes. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Pair of local vibration mode absorption bands related to EL2 defects in semi-insulating GaAs

A pair of correlated bands, which show the same fine structure at low temperature, is discovered in infrared absorption spectra of semi-insulating GaAs crystals. At 80 K the bands peak at 730 cm−1 and 714 cm−1, respectively. According to the fine structures, the spectral linewidths, and the temperature dependence of frequency shifts, the two absorption bands are identified to be induced by local vibration modes of the same defect. As the interconversion of the two bands under some conditions of illumination and temperature variation is very similar to the transformation between the ground state and the metastable state of the EL2 level, these absorptions are ascribed to be related to the EL2 defect.

Temperature dependence of Raman spectra in the mixed system KNO2-NaNO2

The temperature dependence of Raman bands due to internal nodes has been observed on samples with various mixture ratios of NaNO2 and KNO2. The band assigned to the bending mode of NaNO2 shifts to a lower frequency and decreases in intensity as temperature increases. The temperature dependence of frequency shift of the bending mode of KNO2 becomes noticeable with increasing mole fraction of NaNO2. The half-width of the stretching mode increases when the ferroelectric phase transition is approached.

Theory of Exchange Dephasing. II. Quantum Theory of Random Frequency Modulation

With the use of the basic equation derived in the previous paper, the exchange dephasing phenomena are examined by a quantum theory of random frequency modulation. Under a certain circumstance a quantal stochastic process is shown to be the Gaussian-Markoffian process. Time-correlation function and power spectrum are obtained: Temperature dependence of frequency shift and width of line shape is also determined.

Anharmonic effects in cubic crystals

The anharmonic effects due to isochoric self-energy and isothermal volume expansion of cubic crystals have been considered to study the temperature dependence of frequency shifts, low-temperature specific heat and X-ray Debye temperature. The calculated results are in good agreement with the experimental data.