Failure mode transformation of ZnO nanowires under uniaxial compression: from phase transition to buckling

Abstract

The failure modes of ZnO nanowires (NWs) with hexagonal cross section subjected to a uniaxial load are systematically investigated by using molecular dynamics (MD) simulations and two theoretical models considering the surface effect. Our results show that two different failure modes of the phase transition and buckling are triggered when the NWs are under uniaxial compression along the [0001] direction, in which the transformation between the two modes is related to the slenderness ratios of the NWs. Such slenderness-ratio-dependent mode transformation is mainly attributed to the competition between the critical stresses of phase transition and buckling. The Euler and Timoshenko models considering surface effect are further proposed to derive the critical slenderness for such mode transformation. The obtained analytical threshold values agree well with those of present MD simulations. Our results should be of great help for shedding some light on the design and application of functional devices based on ZnO NWs.

Phase transformation and its effect on the piezopotential in a bent zinc oxide nanowire

“…In fact, the study of defect-free ZnO NWs serves as a significant and necessary first step towards the understanding of properties of ZnO NWs containing defects. A defect-free structure has been widely adopted in many previous studies concerning the mechanical [27,30,32], thermal [40] and electronic [40][41][42] properties of ZnO NWs.…”

“…A and ρ in equation (3) are potential parameters mainly determined by the hardness and size of ionic species [50]. Meanwhile, the following Morse-type potential was utilised to calculate the short-range O-O interactions [28,32,50]…”

“…Moreover, the long-range Coulombic interactions among all atoms were described by the Ewald method [51]. It is worth mentioning that the above hybrid Born-Mayer-Morse potential or other potential (Binks potential or Buckingham potential) with a similar expression has been successfully employed in previous studies on the mechanical, piezoelectric and dielectric properties of various ZnO nanomaterials [28,32,45,52,53].…”

“…In addition to tensile loading, compression can also induce the phase transformation in ZnO NWs. Specifically, a compressive load applied to [0001]-oriented ZnO NWs can make them transform from the WZ phase to the HX phase [27,[31][32][33][34]. Meanwhile, a hydrostatic compression can induce a phase transformation from the WZ structure to a rock salt structure in ZnO NWs [27,31].…”

“…According to these findings, it is reasonably assumed that in the practical applications of ZnO NW-based piezotronic nanodevices the phase transformation may occur in their ZnO NW components when the piezotronics are operated by lateral bending. Since ZnO with different lattice structures may possess different material properties [27][28][29][30][31][32][33], the phase transformation that possibly exists in bent ZnO NWs may significantly affect the piezopotential generated in them. Under this circumstance, to more precisely predict the piezopotential generated in bent ZnO NWs, the effect of the phase transformation should be considered in the theoretical modelling; however, this was ignored in previous studies [34][35][36][37][38].…”