Dynamic sound attenuation at hypersonic frequencies in silica glass

Abstract

In order to clarify the origin of the dominant processes responsible for the acoustic attenuation of phonons, which is a much debatted topic, we present Brillouin scattering experiments in various silica glasses of different OH impurities content. A large temperature range, from 5 to 1500 K is investigated, up to the glass transition temperature. Comparison of the hypersonic wave attenuation in various samples allows to identify two different processes. The first one induces a low temperature peak related to relaxational processes; it is strongly sensitive to the extrinsic defects. The second, dominant in the high temperature range, is weakly dependent on the impurities and can be ascribed to anharmonic interactions. The origin of sound attenuation in glasses has been a highly debated topic in recent years. Several models have been proposed but no consensus about the interpretation of sound attenuation has been reached. 1,2,3Several mechanisms responsible for sound attenuation have been identified for over the year:1. interactions of acoustic waves with defects characteristic of the disorder. Those defects are often described as tunneling systems responsible for many anomalous properties of glasses in the low temperature regime. 2. thermally activated relaxational processes, as clearly demonstrated by ultrasonic measurements. 5 The microscopic structural origin of the thermally activated processes is often related to tunneling defects or soft modes responsible for the interaction with acoustic waves. 3. Rayleigh-like scattering by static inhomogeneities, independent of temperature. This has been observed for example in porous glasses (xerogels, aerogels). 7,8 This mechanism yield an attenuation varying like q 4 , where q is the momentum transfer of the interaction in scattering experiment. Rayleigh-like scattering has been also put forward to explain the change of regime for the attenuation in the THz range.3,9 An alternative explanation of the frequency power dependence in ω 4 (where ω = 2π/ν is the pulsation of the excitation) in terms of fractons 10 has been also proposed.4. anharmonicity responsible for the interactions of acoustic waves with thermal phonons, as in crystals. 11,12Each mechanism dominates in different temperature and frequency ranges. It is expected that the mechanisms 1 and 2 are dominant at low temperatures, 3 in very inhomogeneous media or at wavelengths comparable to a few atomic length and the mechanism 4 at high temperature and high frequencies. Moreover, the influence of several parameters have been studied in order to distinguish between universal behavior of the sound attenuation in glasses and more specific properties, related for example to composition effects, or to the method of preparation (impurity concentration or thermal history).13 The influence of pressure, 14 irradiation by neutrons 15,16 or permanent densification 9 has also been investigated.In this paper we present results about Brillouin scattering measurements of sound attenuation at hypersonic frequencies in silica. ...

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

“…The experiment is performed on a spectrosil sample purchased by SILO (Firenze). The sample is characterised by an OH -content of the order of 1500 ppm, that we determined by means of infrared absorption, consistent with similar values found in the literature for the spectrosil samples [22].…”

“…It should however be noted that the OH -content may have a significant influence on the shape and intensity of the attenuation peak found in the temperature dependence at around 150 K, as pointed out in a recent paper [22]. Nevertheless, the OH -content does not affect the attenuation for temperatures outside the peak region, below 50 K and above 250 K, where the discrepancy between our UV measurement and the model (dashed line of figure 5) is evident.…”

Stress-Induced Modification of the Boson Peak Scaling Behavior

“…It is well known that by changing the thermal history or the thermodynamic path to the glass transition the obtained glasses present different elastic properties, both in term of sound velocity and in term of acoustic attenuation [24,25], because of the different amount of internal stresses that develop for the inability of the system to comply with the need to contract under external stimuli [26][27][28][29]. The stress-induced modification of elastic properties in the glass can influence the vibrational dynamics and may have a role in the evolution of the BP.…”

The effect of structural disorder on anomalous critical attenuation of ultrasound by solids

“…In particular, these are thermal processes occurring near the critical point for the liquid -gas system, attenuation of the electromagnetic field energy in the magnetic resonance phenomena, and anomalous attenuation and propagation of acoustic waves in the media under phase transitions. The latter are important due to the fact that they underlie the resonant and ultrasonic methods of investigation of critical dynamics.A unique feature of ultrasonic methods is an anomalously strong attenuation of ultrasound [1][2][3] in the vicinity of the temperatures of the phase transition of the second type, which is vividly revealed in the experiments. This anomalous behavior is due to the effects of interaction of low-frequency acoustic excitations with large-scale fluctuations of the order parameter.…”

“…A unique feature of ultrasonic methods is an anomalously strong attenuation of ultrasound [1][2][3] in the vicinity of the temperatures of the phase transition of the second type, which is vividly revealed in the experiments. This anomalous behavior is due to the effects of interaction of low-frequency acoustic excitations with large-scale fluctuations of the order parameter.…”