High Performance Piezoelectric Crystal Alpha-Bibo for Photoacoustic Gas Detection

The photoacoustic (PA) effect combing with the piezoelectric effect has been designed for trace gas detection, which has been expected to be operational over a wide temperature range. In this paper, the lead-free piezoelectric crystals LiNbO3 (LN), NdCa4O(BO3)3(NdCOB) and $\alpha-$BiB3O6(BIBO) are studied and compared for potential PA trace gas detection. The piezoelectric voltage coefficients of LN $(g21)$, NdCOB $(g12)$ and BIBO $(g21)$ were characterized and found to be on the order of 0.026 Vm/N, 0.047 Vm/N and 0.225 Vm/N at room temperature, respectively. Among the three kinds of piezoelectric crystals, the BIBO crystal possesses the highest longitudinal piezoelectric coefficient $d_{22}$ and the largest piezoelectric voltage coefficient $g_{22}$, being on the order of 40 pC/N and 0.538 Vm$\bullet$/N, respectively. The piezoelectric voltage coefficients for NdCOB and BIBO crystal were obtained to show good temperature stability and maintained the similar values over the temperature range, while the value of $g_{21}$ for LN crystal showed a decrease with increasing temperature. Taking advantage of the strong piezoelectric activity and high mechanical quality factor Q of BIBO crystal, piezoelectric transducer with central resonance frequency of $\sim$443 kHz was fabricated for PA trace gas detection. The final detection limit for trace sulfur hexafluoride (SF6) gas was extended to the parts-per-quadrillion level.