Size-induced transition-temperature reduction in nanoparticles of ZnS

X-ray-diffraction studies of nanometer-sized particles of zinc sulfide show a significant reduction in the zinc-blende-to-wurtzite phase transition temperature, as compared to the bulk value. Five nanoparticle samples were annealed in vacuum at temperatures increasing from room temperature (23 degrees C) to 500 degrees C. Post-anneal analyses revealed an increase of crystallite size, ac companied by a partial transformation from the cubic, zinc-blende structureto the hexagonal, wurtzite structure at temperatures as low as 400 degrees C.This is significantly less than accepted bulk transition temperature of 1020 degrees C. The particles also show some lattice distortion with decreasing particle size and there is a monotonic reduction in the specific volume of about 2.3% as the particle size decreases from al,out 240 to about 30 Angstrom. [S0163-1829(99)04837-7].