Thermally activated relaxation processes in vitreous silica: An investigation by Brillouin scattering at high pressures

Low-temperature phonon damping in vitreous silica explored by UV Brillouin spectroscopy

“…This supports the description of the Akhiezer mechanism in terms of equation (3) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 [12] and US, circles [9]. [15], HiResUv, full circles (present work) and full squares [16], BLS, crosses [26] and dots [20]. …”

“…The five US frequencies have been chosen because they are almost linearly displaced in a logarithmic scale and because of the good quality of the data. These sets of data have been obtained in the past by different authors [12,20,[27][28][29] with slightly different ultrasonic techniques and with different samples, so that a certain discrepancy between the model and the data would not be surprising.…”

“…[15], HiResUv, full circles (present work) and full squares [16], BLS, crosses [26] and dots [20]. [12]; stars: US, 748 MHz [29]; crosses [26] and points [20]: BLS, 35 GHz. The continuous lines are the best fitted functions to the five US data sets with the model of equation (2) GHz, circles (present work and [16]).…”

“…Assuming a uniform distribution of asymmetries, as usually done in the literature (see [20] and references therein), we fixed the parameter σ ∆ at a value much greater than V σ , i.e. with GHz, data is shown in figure 4.…”

“…The frequency and damping of longitudinal phonons of v-SiO 2 at the wavevector 0.071 q nm -1 have been measured in a temperature range from ~10 to 100 K. We will then compare the experimental results for the acoustic attenuation with the prediction of a phenomenological model which takes into account aside the relevant mechanisms of dynamical nature in the explored temperature range, namely the thermally activated relaxation processes [20] also the interaction with the thermal vibrations [21]. Our purpose will be to show how the comparison between the expected behaviour and the measured sound attenuation will indicate the presence of a relevant static contribution in the ultraviolet frequencies, contribution which is, on the contrary, almost negligible in the region explored by BLS.…”