Large electromechanical strain and electrostrictive effect in (1 − x )(Bi 0.5 Na 0.5 TiO 3 –SrTiO 3 )– x LiNbO 3 ternary lead-free piezoelectric ceramics

Lead-free (1 − x )(0.8Bi 0.5 Na 0.5 TiO 3 –0.2SrTiO 3 )– x LiNbO 3 (BNST– x LN, x = 0–0.08) piezoelectric ceramics were fabricated by a solid-state sintered technology. The effects of LN-doping on the structural and electrical properties of the BNST– x LN system were systematically investigated. The results of Raman spectroscopy revealed that the substitution of LN softens the phonon vibrations in the BNST– x LN system, in accordance with the remarkable reduction in the phase transition temperature ( T F−R ), remnant polarization ( P r ), negative strain ( S neg ) and piezoelectric coefficient ( d 33 ). However, the degradation of the long-range ferroelectric orders was accompanied by a significant increase in the electric field–induced strain response. At x = 0.04, a maximum unipolar strain of ~ 0.36% with a corresponding normalized strain ( S max / E max ) of ~ 600 pm/V was obtained at room temperature, which should be mainly ascribed to the reversibly electric field-induced phase transition between the ergodic relaxor and ferroelectric phases due to their comparable free energies in the two-phase coexistence region. Moreover, it was also found that the BNST– x LN system processes predominant electrostrictive behaviors with relatively high electrostrictive coefficient ( Q 33 ) and excellent temperature stability when the field-induced phase transition cannot be trigged by the applied electric field, as evidenced by a fact that the Q 33 value of BNST–0.08LN ceramic keeps almost constant as high as ~ 0.028 m 4 /C 2 in the temperature range from room temperature to 120 °C.