Insights into Strain Engineering: From Ferroelectrics to Related Functional Materials and Beyond

The manifestation of mechanical phenomena in quantum materials at the macroscopic level is intricately linked to pronounced electron‐electron interactions within their lattices, a relationship that becomes especially evident in low‐dimensional materials. Violet phosphorous (VP), a nascent 2D material distinguished by its unique vertically aligned tubular structures, has garnered considerable attention owing to its layer‐dependent electronic bandgap, exceptional carrier mobility, and robust air stability. Herein, a comprehensive exploration of the phonon modes exhibited by few‐layer VP through an integrated experimental‐theoretical approach, focusing on the modulation of their Raman response under the uniaxial strain along a‐axis, b‐axis, and tube direction, respectively, is undertaken. Density functional theory calculations highlight when strain is applied along the a‐ or b‐axis direction, the strain is predominantly mitigated through tube rotational adaptations instead of the change of bond length and bond angle, culminating in a pronounced anisotropic Raman response. Moreover, the strain engineering can effectively optimize the photoelectric response performance of VP, including increase the responsivity ≈2500% and elevate the anisotropic ratio from 2.26 to 3.38. This investigation not only confirms the superior stretchability and impact resistance properties of cross‐structured VP but also establishes the groundwork for exploring the strain‐induced anisotropic optoelectric properties to VP.

Uniaxial Strain Engineering of Anisotropic Phonon in Few‐Layer Violet Phosphorus with High Stretchability for Polarized Sensitive Flexible Photodetector

Shang,

Wang,

Zhang

et al. 2024

Chemical‐Strain‐Engineered Adaptive Interfaces in Nanocomposite Films for Robust Ferroelectricity

Ding,

Tu,

et al. 2024

Strain is an effective means of tuning the crystal structure to obtain a variety of fascinating properties, but how to apply flexible strain to meet the different needs of the film at each location has rarely been reported. In this study, a novel approach for designing strain‐damping structures that facilitate the imposition of flexible strain is introduced. A wide range of strain modulation is demonstrated in SmCoO3 films (a‐axis:+4.5%–+1.7%, b‐axis: +3.2%–+0.4%, c‐axis:+2.2%–+1.4%) under positive pressure by introducing Sm2O3 as a dopant. When SmCoO3 films are subjected to triaxial tensile strain, they exhibit a ferroelectric polarization of 7.12 µC cm−2. Through positive pressure modulation, resulting in a further increase in the ferroelectric polarization (up to 11.62 µC cm−2, which represents the maximum performance of the orthogonal rare earth transition metal oxide family). Moreover, the electron spin order can be effectively controlled, and the film's saturation magnetization increases to 14.83 emu cm−3 (+94.1%). This damping structure allows for flexible modulation of chemical strain in epitaxial film, achieving a delicate balance between film strain and structure, which provides valuable insights for all ferroelectrics based on structural distortion.

Superior Electrocaloric Performance Enabled by Highly Robust Monomorphic Ferrodistortion in NaNbO₃‐Based Relaxor

Li,

Ji,

Wang

et al. 2024

A synergistic realization of high electrocaloric effect (ECE) and excellent temperature stability in ferroelectrics are foundation for practical applications, which is, however, a major challenge in ferroelectric cooling community thus far. In confront with this long‐standing issue, an emergent monomorphic ferrodistortion strategy in NaNbO3‐based relaxor is proposed with flexible tetragonal polar nanoregions immersing in short‐range oxygen octahedral tilt. This not only contributes to large quantities of polar entities to increase entropy change but also produces highly robust oxygen octahedral tilt to persist ferroelectricity and obstruct thermal agitations. Therefore, a high ΔT of 0.96 K and an ultrawide temperature span ΔTspan of 110 K with a record‐high figure of merit of 4.74 is achieved in Ta‐doped NaNbO3‐BaTiO3 ceramics and these superior EC performances present a remarkable breakthrough in ferroelectric bulks cooling. This work thus provides an innovative way of utilizing ferrodistortive relaxor feature with polar nanoregions immersing in oxygen octahedral tilt to simultaneously boost EC value and temperature stability and thus monomorphic ferrodistortion is proposed as an effective strategy to develop high‐performance entropy‐change materials.