Phase transition, electrical properties and large strain response in lead-free (1-x-y)BNT-xBKT-yKNN ceramics

Abstract

Lead-free piezoelectric composition ceramics of (1-x-y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yK_0.5Na_0.5NbO₃; (1-x-y)BNT-xBKT-yKNN (with 0.18≤x ≤ 0.26 and 0≤y ≤ 0.07) were fabricated using the solid-state combustion method. The structure exhibited co-existing rhombohedral and tetragonal phases for all samples. Increasing of x and y contents, the average grain size decreased from 1.42 μm to 1.02 μm and 1.25 μm to 0.70 μm, respectively. The diffuseness exponent (γ) of the ceramics was between 1.817 and 1.939 for x composition and between 1.766 and 1.999 for y composition indicating that the (1-x-y)BNT-xBKT-yKNN solid solutions had diffuse phase transition behavior. The change in the P-E loops of the ceramics indicated that the long-range ferroelectric order of the samples was disturbed and turned to the polar nano-regions (PNRs) with increased x and y contents. The polarization hysteresis loop transformed from well saturated typical ferroelectric, to pinched, and then to the relaxor state with increased x and y content. The addition of BKT and KNN contents significantly enhances the field-induced strain in BNT ceramics. The largest S_max of 0.25% corresponded to a high-field effective d₃₃* of 509 pm/V, which was found in the composition of 0.79BNT-0.20BKT-0.01KNN.

Keywords:

• Phase formation
• dielectric properties
• ferroelectric properties
• strain response
• BNT-BKT-KNN

Acknowledgements

The authors wish to thank Professor David P. Cann at Oregon state university (OSU) and Naresuan University for their supporting facilities. Thanks are given to Dr. Kyle V. Lopin for his help in editing the manuscript.

Additional information

Funding

This work was financially supported by the Thailand Research Fund through the Royal Golden Jubilee Ph.D. Program (Grain no. PHD/0213/2552) to Miss Rattiphorn Sumang and Assoc. Prof. Dr. Theerachai Bongkran.