High-temperature acoustic loss of AT-cut quartz crystals

Sensor applications are increasing the use of quartz crystals at high-temperatures. At these temperatures the interstitial alkalis thermally escape from the traps and drift in the shallow potential wells of the Z-axis channel. Their random motion leads to a thermally activated acoustic loss which may degrade oscillator performance. Point defects may also lead to acoustic loss peaks; Fraser has reported a peak near 300°C in swept quartz. We have investigated the acoustic loss of unswept (Li-compensated), Na-compensated, and swept (H-compensated) AT-cut resonator blanks from room temperature to over 400°C. In swept quartz, we find a loss peak centered at 600 K which increases linearly with the aluminum content. This peak most likely results from relaxation of the Al-OH center. The acoustic loss of unswept and Na-compensated resonators remained relatively constant up to about 500 K; at higher temperatures it increased exponentially with T(K)^-1 . The Al-OH loss peak in the swept blanks with higher Al content caused them to have a larger loss in the 400 to 600 K range than unswept blanks