Atomistic Mechanisms of Ultralarge Bending Deformation of Single-Crystalline TiO₂–B Nanowires

Abstract

Titanium dioxide (TiO 2 ) nanowires (NWs) are usually considered to be brittle semiconductor materials, which limits their use in strain-related applications, even though they are already widely applied in various fields. Based on observations using an in situ transmission electron microscopy method, we find, for the first time, that individual crystalline TiO 2 NWs with a bronze phase (TiO 2 −B) can exhibit an ultralarge elastic bending strain of up to 18.7%. Using an in situ atomic-scale study, the underlying mechanisms of the ultralarge bending deformation of TiO 2 −B NWs under the ⟨111⟩{100} system are revealed to be governed by lattice shear and rich dislocation movements; the lattice shearing is supported by numerical simulations. Locally, large-scale sheared lattices with a shear strain of up to 10.7% can be observed in a bent NW. It is believed that the large-scale lattice shearing deformation offers the NW the ability to absorb a large bending energy so that fast dislocation aggregation and propagation are avoided. Therefore, the TiO 2 −B NWs can endure an ultralarge bending strain without crack formation or amorphization. However, it is found that the lattice shear-governed bending mechanism is not applied in the ⟨010⟩{100} system. These results are able to provide more opportunities for the strain engineering of TiO 2 NWs and also help promote the potential applications of TiO 2 NW-based flexible devices.

Revealing the Mechanical Bending Mechanisms of Single-Crystalline Rutile TiO2 Nanowires Near Room Temperature: Implications for Nanostructured Semiconductors

“…The SF formation, together with the nucleation and glide of the extended dislocations, offers the NWs an ability to accommodate large bending deformations. Our previous works showed that TiO 2 NWs with a pure bronze phase or an anatase/bronze dual-phase could withstand bending strains larger than 10%, largely contributed by rich dislocation movements on the {11̅1}, {100}, and {001} planes in a bronze TiO 2 crystal. , However, the fracture strains of rutile TiO 2 NWs are much smaller than those of the two kinds of TiO 2 NWs, probably because the rutile TiO 2 NWs lack the nucleation and movements of perfect dislocations belonging to other slip systems. Previous work reported that, at high temperature and higher stress conditions, barriers of {110}⟨001⟩ could be overcome by cross-slip, leading to the nucleation and movement of {110}⟨001⟩-type full dislocations. , Since half-dislocations on {101̅} planes can lower the Peierls–Nabarro stress hindering dislocation motion, dissociation of dislocations belonging to {101̅}⟨101⟩ is more likely to occur than the full dislocation slip.…”

“…4 Nanomaterials have a large fraction of atoms residing at or near the surface due to their enormous surface-to-volume ratio, likely resulting in different deformation mechanisms from their bulk counterparts. 5 Many kinds of ceramic nanowires (NWs), such as diamond, 6−8 Si, 9,10 and titanium dioxides (TiO 2 ), 11,12 have been experimentally found to demonstrate large deformations due to the occurrence of dislocation nucleation and movements, deformation twinning, lattice shearing, and others. TiO 2 NWs are attractive in fundamental research and various applications, such as photoelectronics, 13 biomatrixes, 14 and nanoelectrical−mechanical systems.…”

“…Recently, our group found that individual TiO 2 NWs with a bronze phase or a bronze/anatase dual-phase could withstand ultralarge bending strains more than 18% due to large-scale lattice shearing, phase transition, deformation twinning, and full dislocation activities. 11,12 Among all TiO 2 polymorphs, rutile is the most stable phase with a body-centered tetragonal lattice structure. Previous mechanical investigations of bulk rutile TiO 2 at a high temperature revealed that its plasticity was primarily contributed by extended dislocations belonging to the {101̅ }⟨101⟩ slip system.…”

“…Our previous works showed that TiO 2 NWs with a pure bronze phase or an anatase/bronze dual-phase could withstand bending strains larger than 10%, largely contributed by rich dislocation movements on the {11̅ 1}, {100}, and {001} planes in a bronze TiO 2 crystal. 11,12 However, the fracture strains of rutile TiO 2 NWs are much smaller than those of the two kinds of TiO 2 NWs, probably because the rutile TiO 2 NWs lack the nucleation and movements of perfect dislocations belonging to other slip systems. Previous work reported that, at high temperature and higher stress conditions, barriers of {110}⟨001⟩ could be overcome by cross-slip, leading to the nucleation and movement of {110}⟨001⟩-type full dislocations.…”

“…Previous experimental research has well studied the mechanical properties of rutile TiO 2 NWs, including Young’s moduli and yielding strengths. , Direct atomic-scale observation of TiO 2 NWs under deformation is essential to comprehensively understand their mechanical behaviors. Recently, our group found that individual TiO 2 NWs with a bronze phase or a bronze/anatase dual-phase could withstand ultralarge bending strains more than 18% due to large-scale lattice shearing, phase transition, deformation twinning, and full dislocation activities. , Among all TiO 2 polymorphs, rutile is the most stable phase with a body-centered tetragonal lattice structure. Previous mechanical investigations of bulk rutile TiO 2 at a high temperature revealed that its plasticity was primarily contributed by extended dislocations belonging to the {101̅}⟨101⟩ slip system. − However, there have been only atomic-scale investigations on the mechanical properties of rutile TiO 2 NWs using computational methods .…”