Glass-ceramics containing Fresnoite crystals: A potential piezoelectric material for Surface Acoustic Waves generation at high temperature

Most of current piezoelectric sensors are based on ferroelectric ceramics. Nevertheless, the use of ferroelectrics is limited in temperature due to a rapid depolarization over time, as approaching the Curie temperature. Non-ferroelectric piezoelectrics do not present this drawback. However, polycrystalline ceramics are macroscopically piezoelectric only if a preferential orientation of the crystallographic polar axis is induced during the fabrication process. For these compounds, an alternative to single crystals can be found in the glass-ceramic process if a strong preferential orientation of the crystallites is promoted during the crystallization treatment of the parent glass. In the present research, we use this process to produce glass-ceramics containing Strontium-Fresnoite Sr2TiSi2O8. This phase is piezoelectric and non-ferroelectric, with c-axis as polar direction. According to the parent glass composition and the crystallization conditions (mainly temperature and environment), surface crystallization mechanism can be enhanced, leading to preferential orientation of the (00l) lattice plans parallel to the specimens' free surfaces. Usually, a tilt from (00l) to (201) lattice plans is present when penetrating the bulk. Plate specimens (2-3 mm thick) of the obtained glass-ceramics show d33 values ranging between 10 to 14 pC/N. Stability of these materials at high temperatures has been proved by HT-XRD and thermal analyses. Surface Acoustic Waves (SAW) devices have been designed and successfully tested up to 800 °C. The influence of the glass-ceramic composition and microstructure on the characteristics and the evolution of the acoustic signal over temperature is under investigation.