Acoustic relaxation of some lithium borate tungstate glasses at low temperatures

• Ultrasonic attenuation in the glass system, was measured at different frequencies.
• Peaks were attributed to a thermally activated relaxation process.
• Results of activation energy confirmed the glass modification/forming role of WO3.

The longitudinal ultrasonic attenuation in 20Li2O–(80-x) B2O3–xWO3 (0 ≤ x ≤ 12.5) glass system, was measured using pulse echo technique at ultrasonic frequencies 2, 4, 6 and 14 MHz in the temperature range from 150 to 300 K. The absorption curves showed the presence of well-defined broad peaks at various temperatures depending upon the glass composition and operating frequency. The maximum peaks move to higher temperatures with the increase of operating frequency indicating the presence of some kind of relaxation process. This process has been described as a thermally activated relaxation process which occurs when ultrasonic waves disturb the equilibrium of an atom vibrating in a double-well potential in the glass network structure. Results proved that the average activation energy of the process is mainly depending on the modifier content. This dependence was analyzed in terms of the loss of standard linear solid type, with low dispersion and a broad distribution of Arrhenius type relaxation with temperature independent relaxation strength. The experimental acoustic activation energy has been quantitatively analyzed in terms of the number of loss centers (number of oxygen atoms that vibrate in the double well potential).

The longitudinal ultrasonic absorption at low temperatures showed the presence of well-defined peaks whose heights increase as the applied frequency increases. Those peaks were attributed to a thermally activated relaxation governed by Arrhenius relationship. Also, the peak temperature was found to decreases as the WO3 content increases. The activation energy and the attempt frequency were found to increase at two different rates with increasing the WO3 content in the glass system investigated, which means the glass network modification/forming role of WO3, as it cause the elongation of the B–O bonds. Moreover, the number of loss centers was found to be increased with the increase in activation energy, due to the increase in the area under the curve of the longitudinal ultrasonic absorption vs. temperature as the WO3 increases.Figure optionsDownload as PowerPoint slide