Multidirectional Intrinsic Piezoelectricity of 2D Metal Chalcogen-Diphosphate ABP2X6Monolayers

Due to the simultaneously broken inversion symmetries along multiple directions, ABP(2)X(6)(A = Cu or Ag, B = In or Bi, and X = S or Se) monolayers exhibit the coexistence of sizable piezoelectric coefficientsd(11),d(21), andd(31), under unidirectional in-plane strains or stresses, as determined from first-principles calculations. Remarkably, the AgBiP(2)S(6)and AgBiP(2)Se(6)monolayers possessd(11)coefficients of 17.33 and 17.25 pm V-1, respectively; these are much higher than those of extensively studied 2D piezoelectric materials. Meanwhile, the out-of-planed(31)coefficient of AgBiP(2)Se(6)is as high as 0.36 pm V-1. The ABP(2)X(6)monolayers possessing unique multidirectional piezoelectricity pave novel avenues for the application of piezoelectric devices with multiple functions.