LATTICE-DYNAMICS AND HYPERFINE INTERACTIONS IN ZNF2 SINGLE-CRYSTALS

Using the 93.31-keV Mossbauer resonance in Zn-67 the anisotropy of the Lamb-Mossbauer factor (LMF), the quadrupole interaction, and the isom er shift in ZnF2 single crystals have been investigated between 1.1 an d 4.2 K. The anisotropy of the LMF is large: f(x) = (2.4+/-0.1)%, f(y) = (2.3+/-0.2)%, and f(z) = (1.4+/-0.2)%. The main component of the el ectric-field gradient (EFG) tensor V-zz = +(2.18+/-0.22)X10(17) V/cm(2 ) and eta = 0.29+/-0.03 is derived. V-zz is perpendicular to the c axi s. Using a force-constant model (shell model) which includes short-ran ge interactions we solved the eigenvalue problem of the dynamic matrix and quantitatively reproduced the anisotropy of the LMF. Within the s ame model we calculated the second-order Doppler shift. We performed a b initio Hartree Fock (HF) cluster calculations to give a detailed int erpretation of the various electronic contributions to the EFG's at th e Zn and F sites and to the s electron density at the Zn nucleus (isom er shift). The covalent part of the chemical bond essentially determin es all hyperfine interactions. The agreement between HF calculations a nd experiment is very good.