Structure Transformation Of ZnS Nanoparticles Under Pressure

The control of structural transformation in the nanostructure materials is crucial for their practical applications, which requires a basic understanding of the structural transformation of the materials. In the present work, The influences of temperature and pressure on the structural transformation of ZnS nanoparticles have been investigated employing X ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) techniques as following. The sphalerite ZnS nanoparticles with the grain size of d=3.5 nm were prepared by using a direct precipitation method.The structural transformations from the sphalerite structure to the wurtzite structure in ZnS nanoparticles under a pressure of 1 GPa and normal pressure are studied. The results indicate that a lower temperature T =250°C for the structural transformation in ZnS nanoparticles under 1 GPa, as compared to T = 400°C for ZnS nanoparticles under normal pressure. The reduced structural transformation temperature is attributed to that the applied pressure leads to tightly particle-particle contacts, which changes the surface environment of the nanoparticles and thus their surface energy.The effects of annealing pressure, temperature and time on structural transformation from the sphalerite structure to the wurtzite structure of ZnS nanoparticles were systematieally studied. The results indicate that the weight fraction of wurzite phase is approximately invariable after annealing under pressure between 0.4~1.0 GPa. The largest weight fraction of wurzite phase is 17 % after annealing at 300°C for 2 h, the process of structural tansformation is controlled by the sphalerite-wurzite interface.