67Zn Moessbauer spectroscopy

The 93.31-keV Moessbauer resonance in 67Zn is used to determine tiny changes of the transition energy. We first report on a gravitational redshift (GRS) experiment with 67GaZnO single crystal source and 67ZnO powder as absorber. The results on the GRS show that solid state effects which are difficult to control experimentally, in particular the extreme sensitivity of the electric field gradient tensor (efg) in 67ZnO to small external pressure, finally limit the accuracy in determining the GRS. The resonance has been further employed to investigate solid state properties of 67ZnO with high precision. At large pressures 67ZnO exhibits a phase transition from hcp (wurtzite) to fcc (NaCl) structure. The changes of the efg and of the s-electron density ρ(0) at the 67Zn nucleus with reduced unit cell volume show that covalency of the Zn-O bond plays an essential role. We have performed self-consistent Hartree-Fock cluster calculations to describe the experimental changes of ρ(0) in detail. (orig.)