ZN-67-MOSSBAUER STUDY OF NANOSTRUCTURED ZNO

Using the 93.31 keV Mossbauer transition in Zn-67 we have investigated hyperfine interactions and lattice-dynamic effects of nanostructured hexagonal (wurtzite) ZnO. The nanocrystals with particle sizes between 3 and 30 nm were produced by a reactive-gas sublimation method and we re subsequently compacted into solid bodies under external pressure. T he nano-crystalline materials were used as sources in Mossbauer emissi on experiments. A drastic increase of the asymmetry parameter was foun d from eta = 0 (single crystal) to eta approximate to 0.5 (nanostructu red material). Our theoretical Hartree-Fock cluster calculations show that displacements of the Zn atoms off the hexagonal symmetry axis as small as 0.005 Angstrom can lead to such enhanced eta parameters. The Lamb-Mossbauer factor f drastically drops when the particle size is re duced below similar to 10 nm. Two lattice-dynamic models are discussed which successfully describe this behavior.