Instability of CaLi2 at high pressure: Theoretical prediction and experimental results

Hexagonal CaLi2 has been predicted to undergo a bifurcated lattice distortion into polymorphs that may be candidates for superconductivity at high pressure. In this study, density functional and experimental X-ray diffraction techniques are employed to investigate the high-pressure stability of hexagonal CaLi2. Calculated enthalpies of hexagonal CaLi2 and elemental Ca and Li indicate that CaLi2 becomes unstable against segregation at pressures above 7GPa. Our predictions are corroborated by powder X-ray diffraction measurements which show that the application of non-hydrostatic pressure leads to a partial decomposition of CaLi2 to elemental species of Ca and Li. A quantitative phase analysis of hexagonal CaLi2 and cubic Ca clearly shows an increase of the latter for pressures above 14 GPa. Finally, it is suggested that the recently reported superconductivity of CaLi2 at high pressure may contain decomposed Ca and Li. Copyright (C) EPLA, 2009