Investigation of the depolarisation transition in Bi-based relaxor ferroelectrics

Abstract

The loss of macroscopic polarisation in relaxor ferroelectric (Na0.8K0.2)½Bi½TiO3 ceramics doped with BiZn½Ti½O3 has been studied by electrical and structural methods. These indicate that the phenomena that are coupled in a displacive phase transition are not necessarily coupled in the depolarisation of Na½Bi½TiO3-based relaxors and a concept of correlated and uncorrelated switching of dipoles within adjacent unit cells is used to explain this. Second harmonic generation performed on poled ceramics during heating yields values of the freezing temperature and shows a broad temperature range of ∼100 °C across which the structure changes from field-induced ferroelectric to an equilibrium-state ergodic relaxor. Electrical poling at room temperature causes poled regions to increase in size by ∼2 orders of magnitude. A model illustrating the main steps in thermal depolarisation is described that does not require a phase transition to take place on a unit cell level.

Stress-modulated relaxor-to-ferroelectric transition in lead-free(Na1/2Bi1/2Schader1, Wang2, Hinterstein3 et al. 2016Phys. Rev. B885462View full textAdd to dashboardCite

“…The transition temperature T F -R is often defined as the temperature during heating when the thermal fluctuations are large enough to break the electric-field-induced order, resulting in a significant decrease in the small signal piezoelectric response of a poled ferroelectric material [20]. However, it was found in previous investigations [21][22][23][24] that T f and T F -R do not necessarily need to coincide, i.e., the macroscopically poled domain structure thermally depoles at T f but only at the (higher) T F -R disintegrates into polar nanoregions (PNRs). With an increasing temperature above the depolarization temperature, NBT-0.06BT is in an ergodic relaxor state.…”

Local phenomena in bismuth sodium titanate perovskite studied by Raman spectroscopy

“…However, the disruption of ferroelectricity triggers a significant increase in large‐signal piezoelectric strain ( d 33 *) at T FR , which can be attributed to the field‐induced re‐establishment of ferroelectric order from the ergodic relaxor matrix . The polarization current ( j TSDC ) presents a sharp peak at the depolarization temperature ( T d = 85°C), where the poled sample loses the macro‐piezoelectricity . Also, the T d is slightly lower than T FR , since the temperature‐induced ferroelectric‐relaxor transition consists of two separate processes: the detexturization of macrodomains at T d followed by the miniaturization of ferroelectric domains into dynamic PNRs at T FR .…”

Electric‐field induced phase transition and fatigue behaviors of (Bi0.5+x/2Na0.5‐x/2)0.94Ba0.06Ti1‐xFexO3 ferroelectrics

“…On the other hand, as shown in insets of Figure , T d determined by TSDC is, respectively, 103°C, 74°C, and 43°C for BNBT, BNBT‐0.03Fe, and BNBT‐0.06Fe, which has a deviation of 10°C as compared with T F‐R by dielectric anomaly. This deviation is related to that the ferroelectric‐to‐relaxor transition are identified as two separate and discrete processes, which are the losing of the ferroelectric texture and followed by the dissociation of the detextured ferroelectric domains into nanoscale entities …”

“…This deviation is related to that the ferroelectric-to-relaxor transition are identified as two separate and discrete processes, which are the losing of the ferroelectric texture and followed by the dissociation of the detextured ferroelectric domains into nanoscale entities. 38,39 P-E hysteresis loops, associated I-V, bipolar and unipolar strain curves for x=0-0.19 are depicted in Figure 5. BNBT and BNBT-0.03Fe show normal ferroelectric polarization switching behavior.…”