Tuning Ultrafast Photoinduced Strain in Ferroelectric‐Based Devices

Abstract

Ferroelectric materials exhibit coupled degrees of freedom and possess a switchable electric polarization coupled to strain, making them good piezoelectrics and enabling numerous devices including nonvolatile memories, actuators, and sensors. Moreover, novel photovoltaic effects are encountered through the interplay of electric polarization with the material optical properties. Consequently, light‐induced deformation in ferroelectrics, or photostriction, combining photovoltaic and converse piezoelectric effects, is under investigation in the quest for multifunctional materials. Using time‐resolved X‐ray diffraction, the first control of ultrafast photoinduced strain is demonstrated through in situ tuning of the polarization state in ferroelectric‐based devices. Both the magnitude and the sign of the photoinduced strain strongly depend on the transient photoinduced change of the internal electric field in the ferroelectric layer, and can be actively engineered to achieve two distinct remanent photostrictive responses. These results provide fundamental insight into light–matter interaction in ferroelectrics and exciting new avenues for materials functionality engineering.

Photostrictive Effect: Characterization Techniques, Materials, and Applications

“…b) Schematic of the time-resolved X-ray diffraction experiment with external electric filed to adjust the polarization state of the sample. Reproduced with permission [34]. Copyright 2019, Wiley-VCH.…”

Ultrafast photoinduced strain in super-tetragonal PbTiO3 ferroelectric films

“…The lattice expansion of UPS can shift the relative free energies of different phases and induce a transient reversible transformation from a state of coexisting tilted tetragonal-like and rhombohedral-like phases to an untilted tetragonal-like phase in BiFeO 3 thin films [8]. Both the magnitude and sign (contraction and expansion) of the UPS deformation can be tuned by the polarization state through the prepoling, deriving from the internal electric field (imprint field and depolarization field) [10], which is different to the other photoinduced mechanisms such as thermal elasticity [11], electrostriction [12], and charge transfer [13].…”

“…The total photoinduced strain including PP effects-induced strain within 2 ns and positive thermal expansion in tens of nanoseconds has been distinguished. However, in the negative thermal expansion systems of PTO or Pb(Zr x Ti 1−x )O 3 (PZT), the thermal effects have not been investigated to be responsible for the lattice contraction [5,10]. The small compressive strain caused by the negative thermal effect would be overcompensated by the large expansion induced by ferroelectric polarization.…”

Photostriction of NBT-BNT Ceramics

“…半导体材料 [10][11][12][13][14] 及有机材料 [5,[15][16][17][18] 中观察到光致形 变现象，并初步尝试将性能良好的光致形变材料应 用于光机电领域。相较当前微机电系统常用的电致 应变/逆压电效应，光致形变效应有望实现器件的小 型化及无线化 [19][20][21][22][23][24] 。 研究人员通常认为铁电材料的光致形变效是由 反常光伏效应和逆压电效应叠加导致的：铁电材料 在一定光照条件下能够产生显著超过其带隙的光电 压，进而通过逆压电效应引起机械应变 [2,7,25] 。具有 较大光致形变效应的 PLZT 体系是目前最有希望实 现应用的一种铁电材料， 但由于其较大的光学带隙， 仅在紫外光范围内具有光致形变响应，严重限制了 其实际应用范围。此外该体系含有铅元素，对环境 与人体具有一定的危害 [21][22][26][27] 。因此，开发在可 见光范围内具有良好光致形变性能的新型无铅材料 具有十分重要的意义。 Na0.5Bi0.5TiO3-BaTiO3(NBT-BT) 钙钛矿铁电材 料因其良好的综合性能而受到广泛研究。 据文献 [28] 报道，在 NBT-BT 固溶体的 B 位掺杂 Ni 元素能有 效减小其光学带隙，进而提升其对可见光的吸收。 因此，本研究通过在 NBT-BT 体系 B 位掺杂 Ni 元 素形成 Na0.5Bi0.5TiO3-Ba(Ti0.5Ni0.5)O3(NBT-BNT)固 溶体，采用传统固相法结合放电等离子体烧结法制 备高质量 NBT-BNT 陶瓷，并进一步研究该体系在 可见光范围内的光致形变性能。 [3,29] ；并利用 美国福禄克公司 Ti400+热像仪监测样品在光致形 变测试过程中的温度变化；采用美国吉时利公司 PLZT ceramics [26] 0.5 mm 365 150 W/m 2 0.01 3.3 × 10 -10 BiFeO 3 crystal [9] 90 µm 365 326 W/m BiFeO 3 film [8] 35 nm 400 2 mJ/cm Silicon crystal [11] 0.5 mm 248 127 mJ/cm Nematic elastomers [30] -365 -20 -SrRuO 3 film [6] 40 nm 532 62. 图 4 NBT-BNT 样品极化前后的 I-V 曲线 [4] 。极性半导体及铁电材料的 光致形变可能源自反常光伏效应引起的逆压电响应 [3] ，而非极性材料的光致应变可能由光生载流子与 晶格自由度的相互耦合引起 [5][6] 。 最新研究发现未极 化的 PLZT 铁电陶瓷也存在明显的光致应变效应 [31] 。 本研究结果表明， NBT-BNT 陶瓷极化后的反常光伏 电压很小，不足以引起逆压电效应。因此，铁电陶 瓷的光致形变机理也可能与电子与声子或晶格自由 度的强耦合相关： 光生载流子引起强烈的晶格运动， 并进一步导致晶体结构的畸变，进而引起宏观光致 形变。 图 6 NBT-BNT 样品的变温 XRD 图谱…”