Structure and High Performance of Lead-Free (K_0.5Na_0.5)NbO₃ Piezoelectric Nanofibers with Surface-Induced Crystallization at Lowered Temperature

Lead-free potassium and sodium niobate (KNN) nanofiber webs with random and aligned configurations were prepared by the electrospinning process from polymer-modified chemical solution. The crystallization process, structure, composition, dielectric, ferroelectric, and piezoelectric properties of the nanofibers and nanofiber webs were investigated. Theoretical analysis and experimental results showed that the surface-induced heterogeneous nucleation resulted in the remarkable lower crystallization temperature for the KNN nanofibers with the {100} orientation of the perovskite phase in contrast to the bulk KNN gel and thus well-controlled chemical stoichiometry. Low dielectric loss, large electric polarization, and high piezoelectric performance were obtained in the nanofiber webs. In particular, the aligned nanofiber web exhibited further improved piezoelectric strain and voltage coefficients and higher FOM than their thin film counterparts and is promising for high-performance electromechanical sensor and transducer applications.