Electric-field-induced phase transition and pinched P–E hysteresis loops in Pb-free ferroelectrics with a tungsten bronze structure

Abstract

Antiferroelectrics are of interest due to their high potential for energy storage. Here, we report the discovery of pinched, polarization-vs.-electric field (P-E) hysteresis loops in the lead-free tungsten bronze ferroelectrics Ba 4 Sm 2 Ti 4 Nb 6 O 30 and Ba 4 Eu 2 Ti 4 Nb 6 O 30 , while a broad, single P-E hysteresis loop was observed in the analogue compound Ba 4 Nd 2 Ti 4 Nb 6 O 30 . Pinched P-E loops are similar to antiferroelectric hysteresis loops, but in perovskites, they are mostly caused by an extrinsic, internal bias field due to defects, which block domain wall motion. We show that the pinched P-E loops are caused by an intrinsic effect, i.e., by the electric-field-induced phase transition from a nonpolar incommensurate to a polar commensurately modulated crystal structure. The in situ electron diffraction results show the coexistence of commensurate polar structural modulation and incommensurate non-polar modulation during the ferroelectric transition and within the ferroelectric phase below the transition temperature. This phase coexistence is the reason for the small remanent polarization. An external electric field transforms the incommensurate component into a commensurate one, and the polarization increases. This new mechanism for pinched P-E hysteresis loops in ferroelectrics not only indicates a new direction for the development of Pb-free ferroelectric materials for energy storage but also significantly contributes to the physical understanding of ferroelectricity in materials with a tungsten bronze structure.

Neuromorphic nanowire networks: principles, progress and future prospects for neuro-inspired information processing

“…In a related modelling study, Sheldon and Di Ventra [81] showed that activation of disordered memristive networks with strong memory (G on / G off ≫ 1), with an electrical 'crack' appearance, is consistent with a discontinuous (first-order) phase transition, rather than a continuous (secondorder) transition, which is a hallmark of criticality [82]. First-order phase transitions are indicated by hysteresis and have also been observed in ferroelectrics [83] and in models of spiking neural networks [84]. For a randomly diluted lattice network, the authors also found avalanches with power-law size distributions, similar to that observed in neuronal population cultures [34], with an exponent that converges towards the value predicted by mean-field-theory as network size increases.…”

Local Structure and Order–Disorder Transitions in “Empty” Ferroelectric Tetragonal Tungsten Bronzes

“…This backswitching event occurs against an increasingly large electric field with increasing temperature, which indicates increased stability of the disorder with increasing thermal energy. Similar pinched loops in Ba 4 Sm 2 Ti 4 Nb 6 O 30 and Ba 4 Eu 2 Ti 4 Nb 6 O 30 filled TTBs (and later in Ba 4 Sm 2 Fe 0. 5 Ti 3 Nb 6.5 O 30 ) have recently been shown to coincide with a field-driven incommensurate to commensurate transition using in situ electron diffraction.…”

Design of lead-free BCZT-based ceramics with enhanced piezoelectric energy harvesting performances

“…The observed peak splitting in J–E loops could be due to the coexistence of the polar and non-polar phases, which reversibly switch by applying the electric field. 53–55 In addition, Fig. 6c illustrates the room-temperature bipolar S–E plots of the x BTSn samples.…”