High-Acoustic Sensitivity Radiopure Piezoelectric Materials for Dark Matter Detection

Piezoelectric materials are used to fabricate acoustic transducers for bubble chambers in search for particles of dark matter. It has been shown that bubbles initiated by nuclear recoils emit acoustic radiation distinguishable from the phase transitions caused by alpha-decay the main background noise in such searches. However, these piezoelectric materials must exhibit ultralow radioactivity to minimize the neutron background for dark matter detection while possessing high acoustic sensitivity. Here, for the first time, we demonstrate radiopure high-performance piezoelectric ceramics meeting the criteria for acoustic sensing. The screening of radiopure precursors is performed to identify those with low U-238, Th-232, and Pb-210 contents. Using the radiopure precursors, piezoelectric ceramics with varying compositions are synthesized, and their electromechanical acoustic sensing performance is evaluated. Multiple synthesis modifications such as doping and texturing are utilized to tailor the piezoelectric coefficients of the piezoelectric ceramics, and the relationship between the piezoelectric coefficients and acoustic sensing performance of the ceramics is investigated. Acoustic transducers fabricated using textured Pb(Mg1/3Nb2/3)O-3-PbTiO3 (PMN-PT) ceramics are found to exhibit superior acoustic sensitivity due to their high piezoelectric transduction coefficient (d(33) x g(33)). This study demonstrates a useful figure of merit (FOM) for acoustic sensing in bubble chambers.