Structure and piezoelectric properties of K0.5Na0.5NbO3–Bi0.5Li0.5TiO3 lead-free ceramics

Abstract

Lead-free (1−x) K0.5Na0.5NbO3–xBi0.5Li0.5TiO3 + 1 mol% MnO2 piezoelectric ceramics have been prepared by a conventional ceramic technique and their structure and piezoelectric properties have been studied. Our results reveal that Bi0.5Li0.5TiO3 diffuse into K0.5Na0.5NbO3 lattices to form a solid solution with a perovskite structure. The addition of Bi0.5Li0.5TiO3 to the K0.5Na0.5NbO3 solid solution decreases the paraelectric cubic-ferroelectric tetragonal phase transition temperature (TC) slightly, but shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperature (TO−T) significantly to low temperatures. As a result, coexistence of the orthorhombic and tetragonal phases is formed at 0.01 < x < 0.03 near room temperature, leading to a significant improvement in the piezoelectric properties of the ceramics. The ceramic with x = 0.025 exhibits a relatively high TC (392 °C) and optimum piezoelectric properties: d33 = 191 pC/N, kp = 51.5% and kt = 45.5%. The ceramic also exhibit a good thermal stability of piezoelectric properties.