Abstract
The temperature-induced depolarisation of (100-x-y)Na0.5Bi0.5TiO3-xBaTiO3-yK0.5Na0.5NbO3 ceramics has been investigated using polarisation-electric field (P-E) loops, current density-electric field loops, dielectric measurements, thermally stimulated depolarisation current measurements, and x-ray diffraction. The depolarisation temperature (Td) values were measured using the thermally stimulated depolarisation current on each furnace to allow the comparison of results between techniques. Td closely agreed with the values determined from the dielectric anomalies resulting from the ferroelectric to relaxor transition (TF-R). Td determined using pinching of P-E loops was 2–9 K higher, and as the maximum applied electric field was increased, the value of Td increased. The pinching of the loop was shown not to be from an antiferroelectric structure; pinching occurs as the induced ferroelectric phase becomes unstable and returns to its unpoled relaxor state. This is the tuning of the transition from the poled non-ergodic state to the ergodic relaxor state with the applied electric field. Above Td, the P-E loops return to a relaxor state before a reverse field is applied, giving the appearance of a classic antiferroelectric P-E loop.
Highlights
A number of relaxor ceramics have been produced with a polarisation response under an applied electric field that is closer to that seen in an antiferroelectric material than that of a relaxor or ferroelectric
The initial x-ray diffraction (XRD) measurements on as-sintered pellets were consistent for all compositions; they all had single peaks giving rise to a strongly pseudocubic pattern with no discernible peak-splittings
The emergence of a double polarisation-electric field (P-E) response in NBT-based materials occurs as the field-induced ferroelectric state becomes unstable and reverts back to the initial relaxor state
Summary
A number of relaxor ceramics have been produced with a polarisation response under an applied electric field that is closer to that seen in an antiferroelectric material than that of a relaxor or ferroelectric. A number of studies have confirmed this behaviour in NBT, but the structural studies have shown that an antiferroelectric structure does not form.5,6,8,10 Following this initial work, a number of other NBT-based systems have been investigated for their piezoelectric properties, and a common occurrence is the onset of double loops in response to doping and/or increased temperatures. We use the NBT-BT system with the addition of KNN to lower the depolarisation temperature to an accessible range These materials will be used to investigate the region where the P-E loops change from those of a typical ferroelectric to double loops, as determined by Zhang et al..
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