Synthesis and phase transition under ultra-high pressure of ZnS nanoparticles modified by sodium bis(2-ethylhexyl) sulfosuccinate

ZnS nanoparticles modified by AOT with different particle sizes (5 nm and 13 nm) were prepared in reverse micelles. The products show the zinc-blende (B3) structure at atmospheric pressure, and the B3 structure was proved to exist at smaller size dimensions than the B4 structure. The pressure-induced phase transition to the rock salt (B1) phase was studied by in situ high-pressure energy-dispersive X-ray diffraction experiments. The transition began at a pressure of around 15.4 GPa for the 5 nm sample and at 16 GPa for the 13 nm sample. It is indicated that the transition pressure is not obviously dependent on the grain size of the nano-crystals in our experiments. From the small transition pressure gap between the two different sizes it can be deduced that the transition pressure goes to the same value below a certain particle size. This feature could be caused by the crystal lattice contraction due to the strong surface pressure. Our results imply, that the new high-pressure phase is metastable and cannot exist in ordinary circumstances.