A review of potassium sodium niobate and bismuth sodium titanate based lead free piezoceramics

The use of piezoelectric materials is on the rise with their applications as generators, sensors, actuators, and transducers for different purposes such as energy harvesting, strain sensor, active vibration reduction, ultrasonic sonar, distance meter, and distance meter other applications. After its discovery, PZT and lead-based piezoceramics are the main options for choosing a piezoelectric material since they have a high piezoelectric coefficient and high Curie temperature, d33 = 470–610 pC/N and TC= 300–400 °C respectively. However, the current trend of leaving toxic materials, which is backed up by legislative actions of countries, is leading to the replacement of lead-based piezo materials with lead-free piezo materials. Lead-free piezoceramics can be categorized into four groups which are bismuth sodium titanate (BNT) based, potassium sodium niobate (KNN) based, bismuth ferrite (BF) based, and barium titanate (BT) based; however. This study will focus on KNN and BNT based piezoceramics to narrow the scope in order to improve comprehensibility. BF and BT based piezoceramics will be left for the scope of another review study. Improving piezoelectric properties is possible for lead-free piezoceramics by using dopants, improving preparation technique, and achieving coexistence of multiple phases. BNT and KNN based piezoceramics can be prepared to achieve a piezoelectric coefficient as high as d33 = 300–450 pC/N with TC= 250–320 °C. In contrast, BNT based piezoceramics can be prepared to achieve a piezoelectric coefficient as high as d33 = 200–240 pC/N with TC= 300–320 °C. Lead-free piezoceramics with piezoelectric coefficient d33 > 400 pC/N and TC> 300 °C are contenders to replace lead-based piezoceramics, and there exist such KNN based piezoceramics.