Li 2 O at high pressures: structural properties, phase‐transition, and phonons

A structural phase transition in Li 2 O, from the anti‐fluorite to the anti‐cotunnite structure, is evidenced by angle‐dispersive synchrotron X‐ray powder diffraction and supported by ab initio calculations. The equations of state E ( V ), P ( V ) and the enthalpies H ( P ) are determined, for both phases, using total‐energy calculations based on the Projector Augmented Waves method. The calculations supply the value of the transition pressure at T = 0 and in the ‘ideal conditions’ and provide detailed information on all 9 structural parameters describing the anti‐cotunnite structure of Li 2 O at various pressures. We also report Raman frequencies, calculated for both phases and measured in the anti‐fluorite phase, so as to provide a tool for monitoring the approach and the progress of the transformation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)