Novel electro-strain-effect in La-doped Pb(Zr,Ti)O3 relaxor ferroelectrics

Lanthanum doped lead zirconate titanate [(Pb,La)(Zr,Ti)O₃] transparent ceramics show relaxor behavior when the content of Lanthanum is 4-14% and molar ratio of Zr/Ti is 65/35. They were known as important electro-optical materials, but few researches had been focused on their electromechanical behavior. In the present work, we report a large recoverable electrostrain of about 0.2% at 1.0 kV/mm in (Pb,La) (Zr,Ti)O₃ 8/65/35 ceramics. This electro-strain effect is stable over a wide temperature range around its glass transition temperature T_f. In-situ Raman study reveals that the significant strain effect is due to an electric-field-induced reversible transition from a relaxor state to a normal ferroelectric state. A phenomenological explanation based on a revised Laudau theory is given for the origin of the recovery of the initial relaxor state. Such an electro-strain mechanism, being similar to that of the recently-discovered novel superelasticity effect in strain glass system, may provide a novel and general way to achieve ultrahigh electromechanical coupling in relaxor ferroelectrics.