Aging-induced two-step ferroelectric-to-paraelectric transition in acceptor-doped ferroelectrics

It is well known that first-order ferroelectric to paraelectric transition is a one-step transition and it gives rise to one latent heat peak and one permittivity peak during heating. In the present paper, however, we report an unexpected finding; in Mn-doped Ba(Zr0.01Ti0.98Mn0.01)O3-delta the ferroelectric to paraelectric transition proceeds in two steps, after the sample has experienced a prior aging at the differential scanning calorimetry (DSC) peak temperature and followed by cooling down to a fully ferroelectric state. The two-step transition is evidenced by a split DSC peak as well as a split permittivity peak. These abnormal effects can be explained by considering that aging at DSC peak temperature corresponds to aging in a two-phase state (paraelectric+ferroelectric). Such two-phase aging produces two different defect symmetries, which give rise to different stabilities for the same ferroelectric phase and thus results in different reverse transition temperatures.