Multidirectional Intrinsic Piezoelectricity of 2D Metal Chalcogen–Diphosphate ABP₂X₆ Monolayers

Abstract

Reduction in the dimensionality of materials may eliminate the symmetric centers and break the inversion symmetry, [1-5] resulting in piezoelectricity of 2D monolayers, where the mechanical energy is converted into electrical energy and vice versa. Recently, the functional application of 2D piezoelectric materials has been exploited in the field of sensors, [6,7] actuators, [8,9] and energy harvesters. [10,11] Although it has been reported from theoretical calculations that numerous 2D materials, [12,13] such as phosphorene-type α-phase SnSe and SbAs, [14,15] exhibit high intrinsic in-plane piezoelectric d 11 coefficients comparable with d 33 coefficient of bulk lead zirconium titanate (360 pm V À1), [16] thus far, only a few studies have explored the strong intrinsic out-of-plane piezoelectricity of 2D materials, which can be characterized by a high coefficient d 31. Blonsky et al. examined III-V monolayers possessing a 2D hexagonal structure and predicted that the buckled GaP and AlAs exhibit d 31 coefficients of 0.31 and 0.57 pm V À1. [17] In addition, Janus group-III chalcogenide monolayers of GaInS 2 and GaInSe 2 were found to show nonzero d 31 coefficients of 0.38 and 0.46 pm V À1 , respectively. [18] Indeed, in the practical applications of 2D piezoelectric materials, especially in free-standing states, out-of-plane piezoelectricity is more meaningful and should be explored urgently. Recently, a series of lamellar metal chalcogen-diphosphates

Anisotropic correlation between the piezoelectricity and anion-polarizability difference in 2D phosphorene-type ternary GaXY (X = Se, Te; Y = F, Cl, Br, I) monolayers

“…For example, the calculated piezoelectric coefficient of MoS 2 monolayer has been verified exactly by the subsequent experiments [12]. Although the piezoelectric properties of a lot of 2D materials without centrosymmetry have been systematically investigated and those with very large piezoelectric coefficients have been reported [5,10,[16][17][18][19][20][21], it is still quite difficult to accurately determine the origin of piezoelectricity in the 2D materials. Empirical formulas have been proposed to explain the mechanisms of the periodic trend of piezoelectric response in some 2D piezoelectric materials, such as transition-metal dichalcogenide [18], group III-V compounds [18], and group II-VI compounds [22].…”

Anomalous Anisotropy of the Piezoelectric Response in 2D Copper‐Based Ternary Chalcogenides CuMX2

“…Moreover, the much larger piezoelectric coefficients in the range of 9.13–29.52 pm V −1 are obtained in CuMX 2 monolayers. For example, the CuSbSe 2 and CuBiSe 2 monolayers exhibit high coefficients of 29.52 and 26.24 pm V −1 , respectively; obviously, they exceed or approach to those of most well‐studied 2D systems, such as h ‐BN (0.60 pm V −1 ), [ 14 ] MoS 2 (3.73 pm V −1 ), [ 14 ] GaTeF (15.57 pm V −1 ), [ 26 ] SiAs 2 (–17.09 pm V −1 ), [ 22 ] CrTe 2 (17.1 pm V −1 ), [ 17 ] AgBiP 2 S 6 (17.33 pm V −1 ), [ 27 ] α‐AsN (29.14 pm V −1 ), [ 19 ] and P 4 O 2 (54.06 pm V −1 ). [ 20 ]…”

“…Moreover, the much larger piezoelectric coefficients d 12 in the range of 9.13-29.52 pm V À1 are obtained in CuMX 2 monolayers. For example, the CuSbSe 2 and CuBiSe 2 monolayers exhibit high coefficients d 12 of 29.52 and 26.24 pm V À1 , respectively; obviously, they exceed or approach to those of most well-studied 2D systems, such as h-BN (0.60 pm V À1 ), [14] MoS 2 (3.73 pm V À1 ), [14] GaTeF (15.57 pm V À1 ), [26] SiAs 2 (-17.09 pm V À1 ), [22] CrTe 2 (17.1 pm V À1 ), [17] AgBiP 2 S 6 (17.33 pm V À1 ), [27] α-AsN (29.14 pm V À1 ), [19] and P 4 O 2 (54.06 pm V À1 ). [20] Anisotropic piezoelectricity with respect to different-direction strain or stress almost exists in every previously studied 2D systems with C 2v point-group symmetry, such as group IV monochalcogenides, [16] group V binary compounds, [19] and group IV-V binary monolayers.…”

“…Numerous efforts have been made in the past decade to design and develop novel 2D piezoelectric materials for the demand of practical devices. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] It is worth noting that the calculated piezoelectric coefficient of the MoS 2 monolayer has been confirmed by subsequent experiment, [14,18] indicating that theoretical calculation is an effective approach in evaluating piezoelectricity and will play a significant and unique role in studying 2D materials. At the same time, some unique characteristics and mechanisms in 2D piezoelectric materials have been proposed successively, such as anisotropic and multidirectional piezoelectricity, [16,19,24] coexistence of out-of-plane and in-plane piezoelectricity, [15,23] direct correlation between the piezoelectricity and atom polarizability, [15,19,26,28] and layer-dependent piezoelectricity.…”

Monolayer GaOCl: a novel wide-bandgap 2D material with hole-doping-induced ferromagnetism and multidirectional piezoelectricity

“…Piezoelectric materials allow for energy conversion between electrical and mechanical energies, which have been widely used in sensors, actuators, and energy harvesters. Due to the broken centrosymmetry caused by the reduction in their dimensions, 2D materials such as group IV monochalcogenides (SnSe/SnS and GeSe/GeS), 21 the ABX 2 P 6 family, 22 group-V binary compounds (α-SbN, α-SbP, and α-SbAs), 23 III-V semiconductors, 24 and a series of Janus systems, [25][26][27] could exhibit piezoelectricity. Unfortunately, most 2D materials only exhibit in-plane piezoelectricity, which are restricted to use under bending conditions in a functional device.…”