INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 17 (2005) 2625–2632 doi:10.1088/0953-8984/17/17/010 Anomalies in the structure of solid Cd under pressure: an x-ray diffraction study Gabriele Pratesi 1 , Andrea Di Cicco 1,3 , Marco Minicucci 1 and Jean-Paul Iti` e 2 1 Istituto Nazionale per la Fisica della Materia INFM, CNISM and Dipartimento di Fisica, Universit` a degli Studi di Camerino, Via Madonna delle Carceri, I-62032 Camerino (MC), Italy 2 Physique des Milieux Denses, IMPMC, Universit´ e Pierre et Marie Curie, B77, 4 place Jussieu, F-75252 Paris CEDEX 05, France E-mail: andrea.dicicco@unicam.it Received 11 January 2005, in final form 6 March 2005 Published 15 April 2005 Online at stacks.iop.org/JPhysCM/17/2625 Abstract 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 / V 0 ∼ 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. 1. Introduction In the recent past, cadmium metal has been the subject of several theoretical [1–3] and experimental investigations [4–7], mainly because it is known to show anomalies of several physical properties as a function of pressure. Those anomalies are usually related to the occurrence of electronic topological transitions (ETTs) at high pressures. Analogous features have been widely studied in solid Zn, which also crystallizes in the hexagonal close packed (hcp) structure with an unusual large c/a axial ratio (1.856). Evidence for an anomalous feature in solid Cd at P = 3.5 GPa has been observed in thermoelectric power measurements by Godwal et al [6] and by conductivity measurements by Bud’ko et al [8] at the same pressure. The behaviour of the axial ratio of Cd under pressure has been investigated by means of the x-ray diffraction technique [5, 7, 9],where some evidence 3 http://gnxas.unicam.it/ ∼ dicicco 0953-8984/05/172625+08$30.00 © 2005 IOP Publishing Ltd Printed in the UK 2625