Magnetoelectric Multiferroic Janus Monolayers VOXY (X/Y = F, Cl, Br, or I, and X ≠ Y) with In-Plane Ferroelectricity and Out-of-Plane Piezoelectricity

Abstract

Multiferroicity in two-dimensional (2D) materials results from a broken space-inversion and time-reversal symmetry, effecting spontaneous electric polarization and magnetization in the same phase. Recently discovered Janus 2D materials are based on a similar principle, where out-of-plane symmetry is broken to engineer new exciting functionalities, such as an out-of-plane polarization. In this work, a new group of 2D multiferroic Janus monolayers VOXY (X/Y = F, Cl, Br, or I, and X ≠ Y) is derived by breaking the out-of-plane symmetry in the parent multiferroics VOX2. Ferroelectric and magnetic properties of Janus VOXY monolayers are found to be comparable to their parent VOX2 monolayers. In addition to large in-plane piezoelectric coefficients (e 11 from 11.46 × 10–10 to 13.97 × 10–10 C/m, e 12 from −2.54 × 10–10 to −3.32 × 10–10 C/m), most of the Janus VOXY monolayers have significant out-of-plane piezoelectric coefficient. Our theoretical work predicts a new series of 2D multiferroic materials and encourages their further investigation for high-performance nanoelectronic devices.

Versatility of the SiH–CdCl2 Heterostructure: Piezoelectricity, Photocatalysis, and Transistor Applications

“…As a result, the out-of-plane piezoelectric coefficient is 1 order of magnitude higher (Figure c,d) in the case of a biaxial strain (−7.75 pC/m) than that of a vertical strain (−0.76 pC/m). The value of the out-of-plane piezoelectric coefficient in SiH–CdCl 2 heterostructure is comparable to the recently reported 2D materials like Na 2 Te (−4.34 pC/m), Cs 2 S (−16.43 pC/m), Janus MXY monolayers (1–3.8 pC/m; M = Mo or W, X/Y = S, Se, or Te, and ≠ Y), black phosphorus (1.06 pC/m), and Janus VOXY monolayers (−16 to −42 pC/m; X/Y = F, Cl, Br, or I, and X ≠ Y) …”

Multiferroicity in 2D MSX2 (M = Nb and Zr; X = Cl, Br, and I)

“…The polar displacement (P.D.) leads to in-plane ferroelectricity, which can be defined as follows: 53 P.D. = | d M–S2 − d M–S1 |/2,where d M–S2 indicates the long bond length between metal and sulfur atoms, and d M–S1 is the short one.…”

“…To further investigate the FE switching in ZrSX 2 , the piezoelectric parameters were obtained. The piezoelectric strain coefficients are defined as 53,90 d 21 = ( e 21 C 22 − e 22 C 12 )/( C 11 C 22 − C 12 2 ) d 22 = ( e 22 C 11 − e 21 C 12 )/( C 11 C 22 − C 12 2 ),where e ij is piezoelectric stress coefficients and C ij is stiffness tensors. Due to smaller C 22 and larger off-center displacement of metal atoms, the strain coefficients become significant under tension along the direction of FE switching (Table 3).…”

Elemental Semimetal Ferroelectricity in Buckled Carbon Monolayers: Implications for Flexible Field-Effect Transistors

“…It is well-known that symmetry breaking in 2D materials holds significant potential to trigger emerging phenomena. The breaking of symmetry typically induces an intrinsic electric field within the monolayer, resulting in various properties such as ultrahigh carrier mobilities, piezoelectricity, − the Rashba effect, − ferroelectricity, − catalytic properties, and high hydrogen evolution reaction activity . Consequently, exploring symmetry breaking in 2D materials not only sheds light on fundamental physics principles but also holds promise for technological advancements in various fields from electronics to catalysis.…”