Effect of Zr Doping on Structural and Ferroelectric Properties of Lead-Free Bi0.5(Na0.80K0.20)0.5TiO3 Films

Abstract

Environmentally friendly lead-free Bi0.5(Na0.80K0.20)0.5(Ti1−x Zr x )O3 (BNKT-xZr) ferroelectric films with Zr4+ doping concentration x in the range from 0 to 0.05 have been grown on Pt/Ti/SiO2/Si substrates via chemical solution deposition. The effects of Zr4+ substitution on the crystal structure and ferroelectric properties of the films were investigated. X-ray diffraction data revealed that the BNKT-xZr films possessed rhombohedral and tetragonal symmetries at a morphotropic phase boundary when a small amount of Zr4+ doping was added. P–E hysteresis loops typical of ferroelectric materials were observed for all compositions. Zr4+ substituted for Ti4+ in the BNKT-xZr films and remarkably enhanced the ferroelectric properties. The remanent (P r) and maximum polarization (P m) reached their highest values of 14.0 μC/cm2 and 35.7 μC/cm2, respectively, at x = 0.02. These values, which are equivalent to the highest P r and P m values in previous reports on lead-free films with different compositions, compare well with those of Pb(Zr,Ti)O3 (PZT) films. Therefore, BNKT-xZr films with optimal Zr4+ concentration could substitute for PZT films in lead-free piezo-microelectromechanical systems (MEMS) devices.