Phase transitions, relaxor behavior, and large strain response in LiNbO3-modified Bi-0.5(Na0.80K0.20)(0.5)TiO3 lead-free piezoceramics

The effect of LiNbO3 (LN) addition on the ferroelectric behavior and piezoelectric properties of Bi-0.5(Na0.80K0.20)(0.5)TiO3 (BNKT20) lead-free piezoceramics were systematically investigated. Results showed that the LN substitution into BNKT20 induced a transition from coexistence of ferroelectric tetragonal and rhombohedral phases to relaxor pseudocubic phases, which is accompanied by the significant disruption of ferroelectric order and with the shift of the ferroelectric-relaxor transition temperature TF-R down to room temperature. Accordingly, a large accompanying normalized strain of similar to 0.38% (corresponding to a large signal d(33)* of similar to 475 pm/V) were obtained in BNKT20 with 2.5 mol. %LN addition near the phase boundary. Temperature-dependent measurements of both polarization and strain from room temperature to 120 degrees C suggested that the origin of the large strain is due to a reversible field-induced ergodic relaxor-to-ferroelectric phase transformation. Moreover, an attractive property for application as high-temperature dielectrics was obtained in this system modified with 8 mol. %LN with a high permittivity of 1760 +/- 15% from room temperature up to 500 degrees C, spanning a range of about 450 degrees C. (C) 2013 AIP Publishing LLC.