Ferroelectric materials have switchable electrical polarization that is appealing for high-density nonvolatile memories. However, inevitable fatigue hinders practical applications of these materials. Fatigue-free ferroelectric switching could dramatically improve the endurance of such devices. We report a fatigue-free ferroelectric system based on the sliding ferroelectricity of bilayer 3R molybdenum disulfide (3R-MoS ₂ ). The memory performance of this ferroelectric device does not show the wake-up effect at low cycles or a substantial fatigue effect after 10 ⁶ switching cycles under different pulse widths. The total stress time of the device under an electric field is up to 10 ⁵ s, which is long relative to other devices. Our theoretical calculations reveal that the fatigue-free feature of sliding ferroelectricity is due to the immobile charge defects in sliding ferroelectricity.

Ferroelectrics are an integral component of the modern world and are of importance in electrics, electronics, and biomedicine. However, their usage in emerging wearable electronics is limited by inelastic deformation. We developed intrinsically elastic ferroelectrics by combining ferroelectric response and elastic resilience into one material by slight cross-linking of plastic ferroelectric polymers. The precise slight cross-linking can realize the complex balance between crystallinity and resilience. Thus, we obtained an elastic ferroelectric with a stable ferroelectric response under mechanical deformation up to 70% strain. This elastic ferroelectric exerts potentials in applications related to wearable electronics, such as elastic ferroelectric sensors, information storage, and energy transduction.

The discovery of ferroelectric ${\mathrm{HfO}}_2$ in thin films and more recently in bulk is an important breakthrough because of its silicon compatibility and unexpectedly persistent polarization at low dimensions, but the origin of its ferroelectricity is still under debate. The stabilization of the metastable polar orthorhombic phase was often considered as the cumulative result of various extrinsic factors such as stress, grain boundary, and oxygen vacancies as well as phase transition kinetics during the annealing process. We propose a mechanism to stabilize the polar orthorhombic phase over the nonpolar monoclinic phase that is the bulk ground state. Our first-principles calculations demonstrate that the doubly positively charged oxygen vacancy, an overlooked defect but commonly presenting in binary oxides, is critical for the stabilization of the ferroelectric phase. The charge state of the oxygen vacancy serves as a degree of freedom to control the thermodynamic stability of competing phases of wide band gap oxides.

Strontium titanate ($\mathrm{SrTi}{\mathrm{O}}_3$) is regarded as an essential material for oxide electronics. One of its many remarkable features is the subtle structural phase transition, driven by the antiferrodistortive lattice mode, from a high-temperature cubic phase to a low-temperature tetragonal phase. Classical molecular dynamics (MD) simulation is an efficient technique to reveal atomistic features of phase transition, but its application is often limited by the accuracy of empirical interatomic potentials. Here, we develop an accurate deep potential (DP) model of $\mathrm{SrTi}{\mathrm{O}}_3$ based on a machine learning method using data from first-principles density functional theory (DFT) calculations. The DP model has DFT-level accuracy, capable of performing efficient MD simulations and accurate property predictions. Using the DP model, we investigate the temperature-driven cubic-to-tetragonal phase transition and construct the in-plane biaxial strain-temperature phase diagram of $\mathrm{SrTi}{\mathrm{O}}_3$. The simulations demonstrate that the strain-induced ferroelectric (FE) phase is characterized by two order parameters, FE distortion and antiferrodistortion, and the FE phase transition has both displacive and order-disorder characters. In this paper, we lay the foundation for the development of accurate DP models of other complex perovskite materials.

Sliding ferroelectric semiconductors can advance the applications of slidetronics in silicon-compatible microelectronic and optoelectronic devices for the post-Moore era. However, traditional sliding ferroelectrics typically require complex artificial stacking to break symmetry, and most of them lack atomic-scale evidence. Here, we report a sliding ferroelectric semiconductor of naturally parallel-stacked ReSe₂ with layer number N ≥ 3 through rational sliding approach, which is different from the reported sliding ferroelectrics with N ≥ 2. This sliding ferroelectricity avoids the rigorous artificially stacking design. The origin of ferroelectricity arises from the fact that the sliding of arbitrary middle atomic layer breaks the spatial inversion symmetry. We also directly measure the polarization value of ReSe₂ by polarization-electric field hysteresis. Additionally, the electro-tunable ferroelectric polarization is further confirmed by microscopic ferroelectric switching. And, the sliding ferroelectricity enables switchable ferroelectric diode and programmable photovoltaic effect. Our study sheds light on the exploration of sliding ferroelectric semiconductors in naturally parallel-stacked configurations.

Superconductivity has recently been observed in Sr-doped ${\mathrm{NdNiO}}_2$ films grown on ${\mathrm{SrTiO}}_3$. Whether it is caused by or related to the interface remains an open question. To address this issue, we use density-functional theory calculation and charge-transfer self-consistent model to study the effects of polar discontinuity on the electronic and atomic reconstruction at the ${\mathrm{NdNiO}}_2/{\mathrm{SrTiO}}_3$ interface. We find that sharp interface with pure electronic reconstruction only is energetically unfavorable, and atomic reconstruction is unavoidable. We further propose a possible interface configuration that contain residual apical oxygen. These oxygen atoms lead to hybrids of $d_{z^2}$ and $d_{x^2-y^2}$ states at the Fermi level, which weaken the single-band feature and may be detrimental to superconductivity.