Aging-induced double hysteresis loops in bismuth-doped (Ba,Ca)TiO₃ ferroelectric ceramics

Bismuth-doped (Ba_1−xCa_x)TiO₃ ceramics (x = 0.10, Bi-BCT) were prepared by a conventional solid-state reaction technique. An abnormal double-like hysteresis polarization–electric (P–E) loop was observed at room temperature for aged Bi-BCT. Raman scattering gives critical evidence for the formation of O²⁻ vacancies in Bi-BCT. The change from the single P–E loops in the fresh samples to the double loops in the aged samples excludes the existence of a ferroelectric–antiferroelectric transition in Bi-BCT. A reversible domain switching mechanism resulting from a symmetry-conforming short-range ordering of point defects gives a reasonable explanation for the naturally age-induced double-like P–E loops in Bi-BCT.