Large piezoelectric coefficients combined with high electron mobilities in Janus monolayer XTeI (X = Sb and Bi): A first-principles study

Abstract

The absence of both the inversion symmetry and out-of-plane mirror symmetry together with spin-orbit coupling (SOC) can induce novel electronic and piezoelectric properties. In this work, the piezoelectric properties along with carrier mobilities of Janus monolayer XTeI (X=Sb and Bi) are studied by density functional theory (DFT). By using generalized gradient approximation (GGA) plus SOC, they are found to be indirect gap semiconductors with the Rashba spin splitting. The piezoelectric tensors of Janus monolayer XTeI (X=Sb and Bi) are reported by using density functional perturbation theory (DFPT). Due to lacking both the inversion symmetry and out-of-plane mirror symmetry for Janus monolayer XTeI (X=Sb and Bi), both in-plane and out-of-plane piezoelectric effects can be observed, and the large piezoelectric coefficients are predicted (e.g. d11=12.95 pm/V for SbTeI and d11=8.20 pm/V for BiTeI), which are comparable and even higher than ones of many other two-dimensional (2D) materials and other well-known bulk piezoelectric materials, especially for out-of-plane piezoelectric coefficients. With GGA+SOC, the high electron carrier mobilities are obtained, and the electron mobility of BiTeI along armchair direction reaches up to about 1319 cm 2 V −1 s −1 . The carrier mobility shows a rather pronounced anisotropy between electron and hole/armchair and zigzag directions. It is found that tensile strain can improve the piezoelectric coefficients d11 of Janus monolayer XTeI (X=Sb and Bi). For example, at 4% strain, the d11 of SbTeI (BiTeI) is up to 20.12 pm/V (11.48 pm/V), compared with unstrained 12.95 pm/V (8.20 pm/V). Our works imply Janus monolayer XTeI (X=Sb and Bi) have potential applications in flexible electronics and piezoelectric devices, and can stimulate further experimental works.

First-principles study on structural, vibrational, elastic, piezoelectric, and electronic properties of the Janus BiXY ( X=S,Se,T

“…However, the obtained results of d 11 for BiTeY monolayers are much larger than the predicted values for the TMX 2 and Janus TMXY crystals [81,83]. The calculated piezoelectric coefficients, e 11 (d 11 ), of the SbTeI monolayer are reported as 2.69 × 10 −10 C/m (12.95 pm/V), which are slightly larger than their Janus bismuth counterparts [21]. In the case of 1T -TMDs, the piezoelectric coefficients are expected to be very small due to the central symmetry of the structures [59], while for BiXY crystal structures because of lack of inversion and mirror symmetry with respect to the Bi atoms, both in-plane and out-of-plane piezoelectric constants are significant.…”

“…Recently, single-layer (SL) BiTeI composed of three sublayers, with Bi atoms sandwiched between Te and I plates, has been isolated by exfoliation from bulk form [16]. Following this achievement, fascinating properties of BiTeI, including giant RSS [17][18][19], large out-of-plane piezoelectricity [20,21], and high thermoelectric performance (ZT ) [22,23], have been investigated extensively. In addition to BiTeI, various bulk bismuth chalcohalide structures (BiXY with X = S, Se, Te and Y = Cl, Br, I) composed of weakly coupled layers have been synthesized.…”

Exceptional piezoelectricity, high thermal conductivity and stiffness and promising photocatalysis in two-dimensional MoSi2N4 family confirmed by first-principles

“…But it appears that Janus type of MA2Z4 (like upper and bottom parts contain N, Si and P, Ge, respectively) may substantially enhance the flexo coefficient over Janus TMDs, which requires future examinations. When comparing the piezo coefficient of MA2Z4, they show superior piezoelectric coefficient over existing materials like MoS2 [76,86,87], XTeI [88] and Janus TMDs [89,90]. A recent DFT study predicted that SnOSe Janus structure has the highest piezo coefficient of 1.12 nC/m [91] among the known 2D materials.…”

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

“…The piezoelectric coefficients d 11 and d 12 are calculated by Eqs. [11], CrTe 2 [49], SbTeI [50], and phosphorene oxides [51]. From Table 2, we can find that only the d 11 coefficient of GaSeI and the d 12 coefficient of GaTeF are negative, which means that the polarization changes along xdirection decrease with an increase in in-plane stress along x-direction (r 11 ) and y-direction (r 22 ) for GaSeI and GaTeF, respectively.…”