Intrinsic Valley Polarization and High-Temperature Ferroelectricity in Two-Dimensional Orthorhombic Lead Oxide

Abstract

Recent years have witnessed a surge of research in twodimensional (2D) ferroelectric structures that may circumvent the depolarization effect in conventional perovskite oxide films. Herein, by first-principles calculations, we predict that an orthorhombic phase of lead(II) oxide, PbO, serves as a promising candidate for 2D ferroelectrics with good stability. With a semiconducting nature, 2D ferroelectric PbO exhibits intrinsic valley polarization, which leads to robust ferroelectricity with an in-plane spontaneous polarization of 2.4 × 10 −10 C/m and a Curie temperature of 455 K. Remarkably, we reveal that the ferroelectricity is strain-tunable, and ferroelasticity coexists in the PbO film, implying the realization of 2D multiferroics. The underlying physical mechanism is generally applicable and can be extended to other oxide films such as ferroelectric SnO and GeO, thus paving an avenue for future design and fabrication of functional ultrathin devices that are compatible with Si-based technology.

Two-Dimensional Multiferroic δ-PbO Monolayer with a Large In-Plane Negative Poisson’s Ratio

“…Two types of 2D PbO materials, α-PbO and FE-PbO, were proposed from first-principles calculations and predicted to have high stability and valley polarization. 41,42 In this work, we design a new stable 2D PbO monolayer namely δ-PbO, as shown in Figure 1a, which can be obtained from a vdW structure of PbO, as shown in Figure 1b, via exfoliation technologies. First-principles calculations show that the bulk δ-PbO crystal is energetically more favorable than the alreadysynthesized massicot-PbO by about 96 meV/cell, implying the high plausibility.…”

“…Bulk lead oxide (PbO) materials have been intensively investigated and widely applied in many fieldsthe battery paste of lead–acid battery, stabilizer of plastic production, vulcanizing agent of rubber products, glaze additive of ceramic production, ray proof glass, optical glass and crystal glass, and various pigments and coatings. − A van der Waals (vdW) structure of PbO (massicot-PbO) with a layered configuration has also been successfully synthesized in recent experiments, which arouses the subsequent studies of 2D PbO materials. Two types of 2D PbO materials, α-PbO and FE-PbO, were proposed from first-principles calculations and predicted to have high stability and valley polarization. , In this work, we design a new stable 2D PbO monolayer namely δ-PbO, as shown in Figure a, which can be obtained from a vdW structure of PbO, as shown in Figure b, via exfoliation technologies. First-principles calculations show that the bulk δ-PbO crystal is energetically more favorable than the already-synthesized massicot-PbO by about 96 meV/cell, implying the high plausibility.…”

Two‐Dimensional Oxide Crystals for Device Applications: Challenges and Opportunities

“…The atoms within the layers are connected by strong chemical bonds, whereas vertically stacked layers are connected by weak vdW interactions or electro-static forces. [42][43][44][45] Many metal oxides, such as 𝛼-MoO 3 , [46,47] Bi 2 O 2 Se, [48,49] Sb 2 O 3 , [40] SnO, [50,51] PbO, [52,53] WO 3 •H 2 O, [54,55] and V 2 O 5 , [56,57] are demonstrated to own layered crystal structures and stable physical properties. Notably, materials with the same chemical formula may exhibit entirely different crystal structures.…”

2D Oxides for Electronics and Optoelectronics

“…We noticed that the reported 2D oxides contain a variety of structures, such as nonlayered ZnO, [45] Ga 2 O 3 , [46] and MoO 2 , [15] whose atoms are connected by strong chemical bonds in all directions and thus, refrain from a straightforward synthesis of the 2D form. Layered 2D oxides like SnO, [47,48] α-MoO 3 , [49,50] and PbO [51,52] have structures like MoS 2 , in which the atoms are connected by strong chemical bonds within layers and the layers stack together via weak van der Waals (vdW) forces. Sb 2 O 3 is an inorganic molecular crystal, [53] which consists of 0D inorganic molecules of Sb 4 O 6 .…”