We report on quantification and elastic strain mapping in two artificial BaZrO3/BaTiO3 (BZ/BT) superlattices having periods of 6.6 nm and 11 nm respectively, grown on (001) SrTiO3 single crystal substrate by pulsed laser deposition technique. The methodology consists of a combination of high-resolution scanning transmission electron microscopy and nanobeam electron diffraction associated with dedicated algorithm for diffraction patterns processing originally developed for semiconductors to record the strains at atomic scale. Both in-plane and out-of-plane elastic strains were then determined at 2 nm spatial resolution and their average values were used to map the strains along and transverse to the epitaxial growth direction of both samples to determine its variation along several BZ/BT interfaces. In addition, the variation of the width of the inter-diffusion BT/BZ interfaces and intermixing between different layers are estimated. The obtained width average value measured in these inter-diffusion interfaces vary from 8 to 12% and from 9 to 11% for both superlattices having period of 6.6 nm and 11 nm respectively. These inter-diffusion interfaces and the inherent elastic strains due to the confined layers of the superlattices are known to be the most important parameters, responsible of the change in their functional properties.
The stability of high-symmetry $P4mm$ polar phase in eleven ferroelectric perovskite superlattices with the polar discontinuity is studied from first principles. In most superlattices, this phase exhibits either the ferroelectric or the antiferrodistortive instability, or both of them. The structure of the ground state and, for a number of systems, also of metastable phases in these superlattices is found. The spontaneous polarization and piezoelectric properties of superlattices are calculated. The appearance of high piezoelectric coefficients (up to 150-270 pC/N) in some superlattices is ass…
Ferroelectric materials are characterized by degenerate ground states with multiple polarization directions. In a ferroelectric capacitor this should manifest as equally favourable up and down polarization states. However, this ideal behavior is rarely observed in ferroelectric thin films and superlattice devices, which generally exhibit a built-in bias which favors one polarization state over the other. Often this polarization asymmetry can be attributed to the electrodes. In this study we examine bias in PbTiO$_3$-based ferroelectric superlattices that is not due to the electrodes, but rathe…
The polarization response of antiferroelectrics to electric fields is such that the materials can store large energy densities, which makes them promising candidates for energy storage applications in pulsed-power technologies. However, relatively few materials of this kind are known. Here we consider ferroelectric/paraelectric superlattices as artificial electrostatically-engineered antiferroelectrics. Specifically, using high-throughput second-principles calculations, we engineer PbTiO$_{3}$/SrTiO$_{3}$ superlattices to optimize their energy-storage performance at room temperature (to maximi…
Noncentrosymmetric structural transitions in ultrashort ferroelectric AGaO$_{3}$/A'GaO$_{3}$ superlattices
用密度泛函理论研究了八面体倾斜对AGaO $_{3}$ /A 'GaO $_{3}$ [001]，[110]和[111]超晶格（A，A' = La，Pr，Nd）偏心结构转变的影响.我们发现位移跃迁是由两种八面体旋转模式驱动的（a $^{-}$ a $^{-}$ c $^{0}$和a $^{0}$ a $^{0}$ c $^{+}$倾斜），振幅取决于A和A'的化学性质和阳离子的排列方向.我们发现[001]和[111]有序超晶格的基态结构是极性的。八面体倾斜模通过混合反常铁电机制的耦合引起了极位移，产生了宏观电极化的强度。
Charge-order-driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density functional theory to study the effect of artificial structuring on mixed-valence solid-solution La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ (LSFO), a system well-studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits…
Moire materials, created by lattice-mismatch or/and twist-angle, have spurred great interest in excavating novel quantum phases of matter. Latterly, emergent interfacial ferroelectricity has been surprisingly found in spatial inversion symmetry broken systems, such as rhombohedral-stacked bilayer transition metal dichalcogenides (TMDs). However, the evolution of moire superlattices corresponding to polarization switching and hysteresis is still unclear, which is crucial for giving insight into the interplay between lattice symmetry and band topology, as well as developing optoelectronic memory…
Stabilization of highly polar BiFeO$_3$-like structure: a new interface design route for enhanced ferroelectricity in artificial perovskite superlattices
Guidelines for the optimization of hafnia-based ferroelectrics through superlattice engineering
University of Groningen（格罗宁根大学）；Luxembourg Institute for Science and Technology (LIST)（卢森堡科学与技术研究所）；University of Twente（特温特大学）；University of Luxembourg（卢森堡大学）
We construct ferroelectric (LuFeO3)m/(LuFe2O4) superlattices with varying index m to study the effect of confinement on topological defects. We observe a thickness-dependent transition from neutral to charged domain walls and the emergence of fractional vortices. In thin LuFeO3 layers, the volume fraction of domain walls grows, lowering the symmetry from P63cm to P3c1 before reaching the non-polar P63/mmc state, analogous to the high-temperature ferroelectric to paraelectric transition. Our study shows how dimensional confinement stabilizes textures beyond those in bulk ferroelectric systems.
Ferroelectric and photovoltaic properties of BiFeO3/LaFeO3 superlattices grown by pulsed laser deposition have been investigated being the bilayer thickness). For a high concentration of BiFeO3 a ferroelectric state is observed simultaneously with a switchable photovoltaic response. In contrast for certain concentration of LaFeO3 a non-switchable photovoltaic effect is evidenced. Such modulation of the PV response in the superlattices is attributed to the ferroelectric to paraelectric phase transition which is controlled with the increase of x. Remarkably, concomitant to this change of PV mech…
The stability of a high-symmetry $P4mm$ polar phase in seventeen short-period ferroelectric perovskite superlattices with polar discontinuity is studied from first principles within the density-functional theory. It is shown that in most superlattices this phase exhibits either the ferroelectric instability or the antiferrodistortive one, or both of them. For each superlattice, the ground-state structure, the structure of possible metastable phases, the spontaneous polarization, and piezoelectric properties are calculated. The properties of superlattices with the polar discontinuity are compar…
The role of ferroelectric-ferromagnetic layers on the properties of superlattice-based multiferroics
利用脉冲激光沉积技术在（100）SrTiO_3上生长了一系列由铁磁层、铁电层或顺电层组成的超晶格和三层结构。研究了它们的结构和磁电性能。由铁磁Pr 0.85 Ca 0.15 MnO 3（PCMO）和铁电体即Ba 0.6 Sr 0.4 TiO 3（BST）或BaTiO 3制成的超晶格在高施加的磁场下显示出增强的磁阻（MR），而在Pr 0.85 Ca 0.15 MnO 3/SrTiO 3超晶格中不存在这种增强，这清楚地证明了铁电体层在这种增强的MR中的优势作用。在PCMO/BST的三层中没有增强的MR表明在这些系统中导致MR的磁电耦合在多层中比在它们的三层对应物中更强。
Weakly coupled ferroelectric/dielectric superlattice thin film heterostructures exhibit complex nanoscale polarization configurations that arise from a balance of competing electrostatic, elastic, and domain-wall contributions to the free energy. A key feature of these configurations is that the polarization can locally have a significant component that is not along the thin-film surface normal direction, while maintaining zero net in-plane polarization. PbTiO3/SrTiO3 thin-film superlattice heterostructures on a conducting SrRuO3 bottom electrode on SrTiO3 have a room-temperature stripe nanodo…
