Phase transitions from mechanical contraction: direct observation of phase-transition-related volumetric effects in ZnO, GaAs, CaCO₃, and CeNi under compression up to 25 GPa

Pressure-Induced Structural Transformations of ZnO Nanowires Probed by X-ray Diffraction

“…In addition to the traditional synthetic and fabrication routes, external pressure can provide an alternative effective driving force to tune the structures and thus the properties of the nanostructured materials . Therefore, investigations of the structural and phase transformations of nanomaterials under high pressure represent a prevailing materials research frontier. − One of the most interesting observations in those studies is that the compressed nanomaterials behave significantly differently than their corresponding bulk counterparts under pressure. For example, our previous studies on 1D nanomaterials (e.g., SnO 2 nanowires and nanobelts, GaN nanowires, and BN nanotubes) have demonstrated profound implications for producing controlled structures by combined pressure–morphology tuning.…”

“…Under ambient conditions, ZnO has a wurtzite-type (B4) structure (space group P 6 3 mc ) regardless of the morphologies. − The wurtzite phase transforms to a rocksalt-type (B1) phase (space group Fm 3̅ m ) upon compression to some certain threshold pressure (e.g., >8.8 GPa) . This B4-to-B1 phase transition in ZnO has been extensively investigated using different experimental and theoretical approaches, ,,,− but the transition pressure varies in a broad range depending on the morphology of ZnO as well as other experimental conditions. For instance, it was well-established that the B4-to-B1 phase transition for bulk ZnO takes place at ∼9 ± 0.2 GPa. ,− However, the transition pressure for ZnO nanocrystals falls in the broad range from 10.5 to 15.1 GPa as the grain size of the nanocrystals varies from 50 to 12 nm. ,,,− …”

“…This B4-to-B1 phase transition in ZnO has been extensively investigated using different experimental and theoretical approaches, ,,,− but the transition pressure varies in a broad range depending on the morphology of ZnO as well as other experimental conditions. For instance, it was well-established that the B4-to-B1 phase transition for bulk ZnO takes place at ∼9 ± 0.2 GPa. ,− However, the transition pressure for ZnO nanocrystals falls in the broad range from 10.5 to 15.1 GPa as the grain size of the nanocrystals varies from 50 to 12 nm. ,,,− …”