Lead-free ceramics for pyroelectric applications

Abstract

The use of lead-free materials has recently become a very important issue in environmental protection of the earth. Two groups of lead-free ceramics, (K[sub 0.5],Na[sub 0.5])NbO₃ based (KNN) and Bi[sub 1−y](Na[sub x]K[sub 1−x])[sub y]TiO₃ based (BNKT), were studied for their thermal, dielectric, and pyroelectric properties as candidates for pyroelectric sensor applications. The BNKT-based ceramic, [Bi[sub 0.5](Na[sub 0.94]K[sub 0.05]Li[sub 0.016])[sub 0.5]][sub 0.95]Ba[sub 0.05]TiO₃ (BNKLBT), shows excellent pyroelectric properties when compared with KNN-based ceramic and lead zirconate titanate. Its properties were measured as follows: pyroelectric coefficient p=360 µC/m²K, pyroelectric figure of merit of current, voltage, and detectivity F[sub i]=221 pm/V, F[sub v]=0.030 m²/C, and F[sub d]=14.8 µPa[sup −½]. With these outstanding pyroelectric properties, the BNKLBT ceramic can be a promising material for pyroelectric sensor applications. The BNKLBT ceramic with different thicknesses (i.e., 0.3, 0.5, and 0.7 mm) have been used as the sensing element for fabricating infrared detectors. The current responsivity of the sensors was evaluated as functions of frequency.