Effects of A-Site Nonstoichiometry on Dielectric and Piezoelectric Properties of Pb-Free (Na_0.53+xK_0.47)(Nb_0.55Ta_0.45)O₃ Ceramics

Abstract

(Na_0.53+x K_0.47)(Nb_0.55Ta_0.45)O₃ (NKNT) ceramics prepared by a solid state process were investigated at 0 ≤ x ≤ 0.02 to determine the effects of Na content in NKNT ceramics. With Na nonstoichiometry, piezoelectric properties were varied but grains were all cube-like perovskites with no impurity phases. Piezoelectric coefficient (d ₃₃) was sensitive to Na content while polymorphic phase transition (PPT) temperature was not. PPT temperature between orthorhombic and tetragonal phases (T _O-T) was around room temperature within the compositional range tested. The highest d ₃₃ obtained was 330 pC/N at Na_0.545 (x = 0.015) increased from 310 pC/N at Na_0.53 (x = 0), which was due to the morphotropic phase boundary (MPB) effect around (Na_0.53K_0.47) of NKNT ceramics.

Keywords:

• Pb-free sodium potassium tantalum niobate
• nonstoichiometry
• polymorphic phase transition
• morphotropic phase boundary
• piezoelectric coefficient

Acknowledgment

This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MEST) (2011-0030805). This research was also supported by Basic Science Research Program through the National Research Foundation (NRF) of Korea funded by the Ministry of Education, Science and Technology (2011-0026389).