Piezoelectric properties of lead-free (Na_0.5Bi_0.5)TiO₃–(Na_0.5K_0.5)NbO₃–BaTiO₃ ceramics

Abstract

The microstructural evolution and piezoelectric properties of lead-free ceramics (0.98-x)(Na 0.5 Bi 0.5 )TiO 3 -x(Na 0.5 K 0.5 )NbO 3 -0.02BaTiO 3 (0 ഛ x ഛ 0.98, abbreviated as (0.98-x)NBT-xNKN-0.02BT) were investigated. The effects of the amount of NKN on the crystal structure, microstructural evolution, and piezoelectric properties were examined. The 0.93NBT-0.05NKN-0.02BT ceramics having a lower NKN content gave good performances with piezoelectric properties of d 33 ‫ס‬ 140 pC/N and k p ‫ס‬ 21%, because of the soft additive Nb 5+ ions at the B sites. However, a paraelectric cubic phase was observed in the wide range of compositions between x ‫ס‬ 0.1 and x ‫ס‬ 0.9. At a higher NKN content of x > 0.9, a morphotropic phase boundary (MPB) between the tetragonal and orthorhombic phases was found in the 0.015NBT-0.965NKN-0.02BT ceramics, and the piezoelectric properties were enhanced (d 33 ‫ס‬ 135 pC/N, k p ‫ס‬ 29%). The piezoelectric properties of this system were closely related to its crystal structure.