INELASTIC NEUTRON-SCATTERING FROM SINGLE-CRYSTAL ZN UNDER HIGH-PRESSURE

Inelastic neutron-scattering experiments have been performed for singl e crystals of Zn under pressures up to 8.8 GPa at 300 K. The phonon mo des q/q(max) = xi = 0.075 and xi = 0.10 were measured in the transvers e acoustic branch Sigma(3), where q = 0 corresponds with the elastic c onstant C-44. The phonon energy showed a substantial hardening with in creasing pressure. The experimental data below 6.8 GPa for xi = 0.075 yield a constant Gruneisen mode gamma(i) = - In omega(i)/InV of 2.25 i n good agreement with a previous calculation [H. Ledbetter, Phys. Stat us Solidi B 181, 81 (1994)]. Above 6.8 GPa, there is a very rapid incr ease of yi which is indicative of the presence of a giant Kohn anomaly . This rapid divergence at high pressure indicates that a phonon softe ning may occur at pressures higher than 8.8 GPa caused by the collapse of the giant Kohn anomaly via an electronic topological transition (E TT). In an earlier Mossbauer Zn study at 4 K [W. Potzel et al., Phys. Rev. Lett. 74, 1139 (1994)], a drastic drop of the Lamb - Mossbauer fa ctor was observed at 6.6 GPa, which was interpreted as being due to ph onon softening, indicating this ETT had occurred. This paper also comp ares the compressibility data for single crystal Zn and Zn powder usin g neutron scattering. The results were found to be similar to an earli er x-ray Zn powder experiment [O. Schulte et al., High Pressure Res. 6 , 169 (1991)].