Structural evolution and electromechanical properties of SrTiO3-modified Bi0.5Na0.5TiO3–BaTiO3 ceramics prepared by sol-gel and hydrothermal methods

This article reports structural evolution and electromechanical properties of lead-free (1-x)(0.965Bi0.5Na0.5TiO3-0.035BaTiO3)-xSrTiO3 (BNTBT-100xST with x = 0.00–0.30) ceramics synthesized by sol-gel and hydrothermal methods. The crystal structure investigation shows a compositionally-driven phase transition from the dominant rhombohedral (R) phase to the tetragonal (T) phase. However, the physical properties revealed that BNTBT converts from normal ferroelectric to relaxor ferroelectric due to the disruption of long-range ferroelectric order with ST modifications. Highest electric field-induced strain coefficient (d 33* = 320 pm/V) for the optimum composition was attributed to the crystal structure morphotropic phase boundary of the R and T phases. A phenomenological explanation from the ferroelectric properties strongly supports the argument of the high piezoelectric strain response. A phase diagram was developed based on the crystal structure, dielectric, ferroelectric and piezoelectric properties that provide a systemic correlation and better elucidation of the BNTBT-100xST ceramic system.