An Unconventional Transient Phase with Cycloidal Order of Polarization in Energy‐Storage Antiferroelectric PbZrO₃

Abstract

Antiferroelectric‐based dielectric capacitors are receiving tremendous attention for their outstanding energy‐storage performance and extraordinary flexibility in collecting pulsed powers. Nevertheless, the in situ atomic‐scale structural‐evolution pathway, inherently coupling to the energy storage process, has not been elucidated for the ultimate mechanistic understanding so far. Here, time‐ and atomic‐resolution structural phase evolution in antiferroelectric PbZrO3 during storage of energy from the electron‐beam illumination is reported. By employing state‐of‐the‐art negative‐spherical‐aberration imaging technique, the quantitative transmission electron microscopy study presented herein clarifies that the hierarchical evolution of polar oxygen octahedra associated with the unit‐cell volume change and polarization rotation accounts for the stepwise antiferroelectric‐to‐ferroelectric phase transition. In particular, an unconventional ferroelectric category—the ferrodistortive phase characteristic of a unique cycloidal polarization order—is established during the dynamic structure investigation. Through clarifying the atomic‐scale phase transformation pathway, findings of this work unveil a new territory to explore novel ferrodistortive phases in energy‐storage materials with the nonpolar‐to‐polar phase transitions.

Unveiling the ferrielectric nature of PbZrO3-based antiferroelectric materials

“…Nonetheless, early work has demonstrated that the prototypical PbZrO 3 showed multiple soft-mode vibrations, which mainly involved trilinear coupling between vibrations of Pb cations and librations of oxygen octahedra 24 . Moreover, the very recent work on the electron-beam illumination induced phase transition in PbZrO 3 single crystals clearly showed the hierarchical evolution of oxygen octahedra 25 . Thus, as an important component in perovskite PbZrO 3 -based materials, the information of oxygen octahedra should be essentially taken into account for comprehending structure-property correlation and developing AFE/FiE theories.…”

In Situ Observation of Point‐Defect‐Induced Unit‐Cell‐Wise Energy Storage Pathway in Antiferroelectric PbZrO3

“…Meanwhile, the defect core initiates an AFD‐to‐FD transition in a stripe region with width of ≈ b AF along x direction, which is characterized by y ‐direction transformation of oxygen shifts from (0 ↓ 0 ↑)/(0 ↑ 0 ↓) in the AFD state to (0 ↓ ↑ ↑)/(0 ↑ ↓ ↓) in the FD‐I state. [ 14 ] Herein, the zeros “0” marked by red solid line denote oxygen atoms locating at the centrosymmetric positions. This reveals that polar distortion occurs to the oxygen octahedral in the FD state, which generates a polarization with P S ≈ 3 µC cm −2 that essentially runs along direction according to previous TEM measurement [ 14 ] (Figure S2b, Supporting Information).…”

“…[ 14 ] Herein, the zeros “0” marked by red solid line denote oxygen atoms locating at the centrosymmetric positions. This reveals that polar distortion occurs to the oxygen octahedral in the FD state, which generates a polarization with P S ≈ 3 µC cm −2 that essentially runs along direction according to previous TEM measurement [ 14 ] (Figure S2b, Supporting Information). As the irradiation time increases to t = 20 s, the FD‐I state expands in unit‐cell wise along y direction, which is accompanied with dynamic size change of the defect core.…”

“…[ 10–13 ] On the one hand, it is reported that the illumination electron beam in transmission electron microscopy (TEM) may act as an external stimulus to slow down the excitation and image the structural phase transition in real time. [ 14,15 ] This endows a possibility of probing the storage process of energy through atomic‐resolution TEM imaging (Figure 1a). On the other hand, the small critical thickness (≈6.5 nm) provides a favorable condition for resolving the structural order parameters, [ 16,17 ] for example, tilting of oxygen octahedra, [ 18,19 ] and dynamically tracking their evolution during the AFE‐to‐FE transition.…”

“…Here, based on excitation of illumination electron beam, [ 14,29,30 ] we investigate in situ the impact of oxygen‐lead‐vacancy‐induced defect structure on phase transitions of PbZrO 3 during energy storage in an image‐corrected TEM. By simultaneously imaging light oxygen anions and heavy cations using negative spherical‐aberration imaging (NCSI) technique, [ 17,31,32 ] our time‐resolved dynamic study reveals that with retention of antiparallel Pb displacements, the vacancy‐driven defect structure triggers an antiferrodistortive‐to‐ferrodistortive (AFD‐to‐FD) state transition in a stripe manner with variable width at unit‐cell‐wise level.…”