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Lead free Bi0.5 (Na1-xKx)0.5TiO3 piezoceramics (BNKTx) with various amount of potassium (x=0.18, 0.20, 0.22 and 0.24) around morphotropic phase boundary (MPB) were prepared via a conventional solid state reaction. The crystal structure, electrical properties and strain were significantly influenced by the amount of K+ substitution. The XRD patterns revealed that by increasing K+ amount the tetragonal phase increased as well as more K+ content resulted in the enhanced piezoelectric properties, a large piezoelectric constant d33=195 pC/N was obtained at x=0.20, however depolarization temperature (Td) reached to 100 oC. The BNKTx ceramics exhibited high remnant polarization Pr= 37.50 µC/cm2 of the MPB composition (x=0.20). The increase of K+ content destabilized the ferroelectric order of the BNKTx ceramics, leading to degradation of the remnant polarization, reduction of coercive field and changing the shape of hysteresis loop towards antiferroelectric phase. An outstanding large electric field induced strain (S=0.13%) under 1 kV/mm and normalized strain d_33^*= 1320 pm/V were obtained at the MPB for x=0.20

Keywords: Piezoelectric, Lead-free, BNKT, Strain

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