c/a anomalies, thermoelectric power and electronic topological transitions in Cd

Thermoelectric power (TEP) measurements up to 6.9 GPa pressure and the total energy calculations for the axial ratio (c/a) variation with compression were carried out for cadmium. We find two anomalies as compared to a single anomaly observed in the experimental X-ray diffraction (XRD) data. The first anomaly at V/ V₀ = 0.95 is due to electronic topological transition (ETT) and correlates well with our TEP data, and with the anomaly observed in the existing resistivity data. The second anomaly at V/V₀ = 0.85 correlates well with the recent high-precision imaging plate-based XRD data. We attribute the 4d-orbital overlap, coupled with transfer of electrons from d to s states as the cause of this anomaly. This finding is in contrast to the existing understanding in zinc, where the c/a anomaly is attributed to the destruction of a giant Kohn anomaly by ETT. Non-destruction of the giant Kohn anomaly in cadmium shows that the Fermi surface of Cd is different from that of Zn at high pressures.