Enhanced piezoelectric properties near the morphotropic phase boundary in lead-free (1-x)(Bi0.5K0.5)TiO3-xBi(Ni0.5Ti0.5)O3 ceramics

• We fabricated new solid solution of (Bi0.5K0.50)TiO3–Bi(Ni0.50Ti0.50)O3.
• New MPB region of 0.05 < x < 0.10 was observed with excellent electrical properties.
• BKT-0.10BNiT presented high d33 = 288 pC/N, Smax = 0.22% and d*33 = 313 pm/V.

Lead-free piezoelectric ceramics of the composition (1-x)(Bi0.5K0.50)TiO3-xBi(Ni0.50Ti0.50)O3 or (1-x)BKT-xBNiT (when x = 0–0.20 mol fraction) were prepared by a conventional mixed-oxide method and sintered at 1050 °C for 4 h. The effects of BNiT content on the phase equilibria, and the dielectric, ferroelectric and piezoelectric properties were systematically investigated. High density sintered specimens (5.71–6.12 g/cm3) were obtained for all compositions. X-ray diffraction patterns showed that all BKT-BNiT samples exhibited a single perovskite phase which confirms that BNiT and BKT formed a solid solution up to x = 0.20. A morphotropic phase boundary (MPB) separating a BKT-rich tetragonal phase and a BNiT pseudo-cubic phase was identified over the compositional range 0.05 < x < 0.10, where enhanced electrical properties were observed. The optimum dielectric properties (εr = 1710, tanδ = 0.036), ferroelectric properties (Pr = 16.6 μC/cm2, Ec = 22.5 kV/cm and Rsq = 0.86) and piezoelectric properties (d33 = 288 pC/N, Smax = 0.22% and d*33 = 313 pm/V) were observed with a relatively high Tm ∼ 304 °C within this MPB region. Overall, these results indicate that the BKT-BNiT ceramic system is a promising lead-free piezoelectric candidate for further development for actuator applications.

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