Polymorphism and Formation Mechanism of Nanobipods in Manganese Sulfide Nanocrystals Induced by Temperature or Pressure

Abstract

Manganese sulfide (MnS) nanocrystals (NCs) with three different phases were synthesized by one-pot solvent thermal approach. The crystal structures and morphologies were investigated using powder X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. We found that the crystal structure and morphology of MnS NCs could be controlled by simply varying the reaction temperature. The detailed growth process of MnS nanobipods, including the zinc blende (ZB)-core formation and wurtzite (WZ)-arms growth, provides direct experimental evidence for the polymorphism model. Furthermore, we have studied the stability of metastable ZB- and WZ-MnS NCs under high pressure and found that ZB-nanoparticles and ZB/WZ-nanobipods are stable below their critical pressure, 5.3 and 2.9 GPa, respectively. When pressures exceed the critical point, all these metastable MnS NCs directly convert to the stable rock salt MnS