Large in-plane and out-of-plane piezoelectricity in 2D γ-LiMX2 (M=Al, Ga and In; X=S, Se and Te) monolayers

Giant intrinsic piezoelectricity in 2D hybrid organic–inorganic perovskites [C6H11NH3]2MX4 (M = Ge, Sn, Pb; X = Cl, Br, I)

“…From the illustration in Fig. 6(a), it is clear that compared with other 2D monolayers, 27,29,53–60 [C 6 H 11 NH 3 ] 2 MX 4 have larger piezoelectric stress coefficients e ij . It means that they shall have larger out-of-plane piezoelectric coefficients d 31 and d 32 according to formula (4).…”

“…This value is 2 orders of magnitude larger than other reported 2D monolayers which include 2D Buckled hexagonal III–V compounds ( d 31 = d 32 = 0.016–0.568 pm/V), 27 Janus structures of quintuple Bi 2 X 3 (X = S, Se) monolayers (| d 31 | = | d 32 | = 0.18–0.20 pm V −1 ), 29 Janus niobium oxydihalide, NbOXY (X, Y = Cl, Br, I and X ≠ Y) ( d 31 = 0.002–0.074 pm V −1 ; d 32 = 0.26–0.34 pm V −1 ), 53 2D M 2 CO 2 (M = Sc, Y, La) MXenes ( d 31 = d 32 = 0.42–1.16 pm V −1 ), 54 Janus transition metal dichalcogenides ( d 31 = d 32 = 0.007–0.028 pm V −1 ), 48 two-dimensional Janus Si dichalcogenides ( d 31 = d 32 = 0.157–0.31 pm V −1 ), 55 Janus group-III chalcogenide monolayers ( d 31 = d 32 = 0.007–0.46 pm V −1 ), 56 group-IV(A) Janus dichalcogenide monolayers ( d 31 = d 32 = 0.11–0.26 pm V −1 ), 57 Janus structures in semiconducting group IVB dichalcogenide monolayers (2D-NS MXY) ( d 31 = d 32 = 0.004–0.414 pm V −1 ), 58 and 2D monolayer Li-based ternary chalcogenides LiMX 2 (M = Al, Ga and In; X = S, Se and Te) ( d 31 = d 32 = 0.05–1.62 pm V −1 ). 46,59 In addition, [C 6 H 11 NH 3 ] 2 SnBr 4 does not contain Pb element, and there is no Pb pollution when it is used in the piezoelectronic device. This discovery can expand the practical applications of lead-free piezoelectric materials in piezoelectronic devices, such as loudspeakers, flexible pressure sensors and vibration energy harvesters.…”

“…From the illustration in Fig. 6(a), it is clear that compared with other 2D monolayers, 27,29,[53][54][55][56][57][58][59][60] value indicates that the lattice will stretch (compress) along the a-axis (b-axis) when the applied electric field is along the c-axis direction. The significant difference between the intramolecular bond energies (Fig.…”

“…53,54 In particular, the out-of 54 Janus transition metal dichalcogenides (d 31 = d 32 = 0.007-0.028 pm V −1 ), 48 two-dimensional Janus Si dichalcogenides (d 31 = d 32 = 0.157-0.31 pm V −1 ), 55 Janus group-III chalcogenide monolayers (d 31 = d 32 = 0.007-0.46 pm V −1 ), 56 group-IV(A) Janus dichalcogenide monolayers (d 31 = d 32 = 0.11-0.26 pm V −1 ), 57 Janus structures in semiconducting group IVB dichalcogenide monolayers (2D-NS MXY) (d 31 = d 32 = 0.004-0.414 pm V −1 ), 58 and 2D monolayer Li-based ternary chalcogenides LiMX 2 (M = Al, Ga and In; X = S, Se and Te) (d 31 = d 32 = 0.05-1.62 pm V −1 ). 46,59 In addition, [C 6 H 11 NH 3 ] 2 SnBr 4 does not contain Pb element, and there is no Pb pollution when it is used in the piezoelectronic device. This discovery can expand the practical applications of lead-free piezoelectric materials in piezoelectronic devices, such as loudspeakers, flexible pressure sensors and vibration energy harvesters.…”

A Review of Ultrathin Piezoelectric Films

“…This is owing to the unique double-buckled stacking structure of these LiMX 2 monolayers [87]. Later, it was found that γ phase structure (γ-LialS 2 and γ-LialSe 2 ) also has an excellent out-of-plane piezoelectric coefficient; even the number is twice as high as that of β phase structure [88]. When compared with the piezoelectric coefficients of other materials as shown in Figure 15, it is evident that the γ-LiMX 2 structures are very promising materials for high-performance piezoelectric nanodevices.…”