Large Strain Response in 0.99( Bi0.5 Na0.4 K0.1) TiO3-0.01( K x Na1− x) NbO3 Lead-Free Ceramics Induced by the Change of K/ Na Ratio in ( K x Na1− x) NbO3

Influence of K/ Na ratio in ( K _x Na_{1− x}) NbO₃ on the ferroelectric stability and consequent changes in the electrical properties of 0.99( Bi_0.5 Na_0.4 K_0.1) TiO₃-0.01( K _x Na_{1− x}) NbO₃ ( BNKT- K _x NN) ceramics were investigated. Results showed that change of K/ Na ratio in KNN induces a phase transition from ferroelectric to ergodic relaxor phase with a significant disruption of the long-range ferroelectric order, and correspondingly adjusts the ferroelectric-relaxor transition point T_F−R to room temperature. Accordingly, giant strain of ~0.46% (corresponding to a large signal d₃₃* of ~575 pm/V) which is comparable to that of Pb-based antiferroelectrics is obtained at a K/ Na ratio of ~1, and the emergence of large strain response induced by the change of K/ Na ratio of KNN can be well explained by the correlation between the position of ferroelectric-ergodic relaxor phase boundary in the BNKT-K _x NN system and the tolerance factor t of the end number ( K _x NN). In situ high-energy X-ray scattering experiments with external field reveals that the large strain response in the studied system is likely related to the electric field-induced distortion from the pseudocubic structure. [ABSTRACT FROM AUTHOR]