Anomalies in the structure of solid Cd under pressure: an x-ray diffraction study

The results of an x-ray diffraction energy-dispersive study on solid Cd under high-pressure conditions at room temperature are presented. The trends of the lattice parameters and of the axial ratio c/a as a function of pressure show that an anomalous slope change, previously discussed in connection with an electronic topological transition (ETT), is still observed using a different pressure transmitting medium for relative volume compression V/V0∼0.86. A detailed study of the peak positions shows that some Bragg reflections, in particular those related to the length of the c axis, are shifted with respect to the calculated positions for a typical hcp structure. This anomalous behaviour, observed for pressures above 4 GPa, is briefly discussed in terms of possible oriented lattice strains and non-hydrostatic effects