High-Pressure X-ray Diffraction Structural Study of Zr: Reinvestigation of the Isostructural BCC→BCC Phase Transition and EOS Determination up to 210 GPa*

Interplay between structural transitions and electronic and lattice dynamics properties under pressure is of one the fundamental issues in condensed matter physics. The structural evolution of Zr under pressure had attracted substantial interest due to the possibility of an isostructural BCC→BCC phase transition at 57 GPa. Akahama et al. suggested that this transition is triggered by a s-d electronic transition. Follow up theoretical studies ruled out the electronic transition and questioned the existence of the structural transition. In this study we have performed a detailed structural study of Zr up to 210 GPa. We confirm the isostructural transition and we don't observe any subsequent phase transition up to the highest pressure of this study. We have used density functional theory to investigate zirconium in the isostructural transition region. The pressure-volume curve is smooth, without any indication of a band crossing. DFT phonons have been calculated, and show no indication of anomalies that could drive a phase transition. A more comprehensive theoretical approach seems to be needed.