Pressure Induced Phase Transitions and EOS Derived for Laves Phase Deuterides ErFe2Dx (x = 1.35, 1.9 and 3.4)

The energy dispersive X-ray diffraction patterns of ErFe2Dx deuterides [where x = 1.35 (alfa1 phase), x = 1.9 (alfa2 phase) and x = 3.4 (beta phase)] have been measured under pressure up to 31 GPa. Compression curves and equation of state (EOS) parameters were determined us ing ex per i men tal data. ErFe2D1.35 and ErFe2D1.9 de com posed into phases with low (alfa1 ,, alfa 2 ,) and high (alfa1 ,, alfa 2 ,,) deuterium concentrations around 8 GPa. As the pressure was raised above 8 GPa, the D con cen tra tion in the alfa1 ,, alfa 2 , phases re mained close to about x = 0.2 whereas in the alfa1 " alfa 2 ,, phases it in creased from x = 2.1 to a max i mum of x = 4.6 at about 20 GPa. This was accompanied with a progres sive distortion of the alfa1 ,, alfa 2 ,, phases from a cubic to wards an orthorhombic structure. This decomposi tion process occurs with a large hysteresis effect between loading and unloading cycles. A similar decomposition into beta , and beta ,, phases seem ingly oc curs also for ErFe2D3.4 at 11 GPa being accompanied with a change of initial rhombohedral (R3m) symmetry to another one. The D content in this new beta" phase (x ~4.6) be comes close to that of orthorhombic ErFe2H5. These processes have character of spinodal decomposition and are related to a lowering of its critical temperature upon applied pressure.