Phase structure and piezoelectric properties in K/Bi co-doped AgNbO3 lead-free ceramics

Abstract

The ferroelectric (FE) and anti-ferroelectric (AFE) properties of AgNbO3, an AFE material, can be altered by ion doping. K-doping is an effective strategy to enhance the FE properties by inducing an AFE-FE phase transition in the AgNbO3 ceramics, which boosts the FE and piezoelectric properties of (Ag,K)NbO3 ceramics. In this study, the phase structure and piezoelectric properties of the (Ag,K)NbO3 ceramics were further optimized via Bi doping. Doping with a small amount of Bi shifted the orthogonal-tetragonal (O-T) phase boundary to a lower temperature, leading to enhanced piezoelectric properties at room temperature in the (Ag0.9-3xK0.1Bix)NbO3 (x = 0.01–0.04) ceramics. The room-temperature phase structure of the ceramics changed from the FE phase to the AFE phase as x was increased from 0.01 to 0.04. A d33 of 83 pC/N was obtained for the (Ag0.84K0.1Bi0.02)NbO3 ceramics at room temperature, which increased to 140 pC/N at the O-T phase boundary. This study further reveals the controllable phase structure of AgNbO3-based ceramics for their potential applications as piezoelectric ceramics.