High pressure phase transitions in scheelite structured fluoride: ErLiF4

Our synchrotron based angle dispersive x-ray diffraction studies on scheelite structured ErLiF4 show that it undergoes two phase transitions, at similar to 11.5 and similar to 15.5 GPa to lower symmetry monoclinic phases, before becoming (irreversibly) amorphous at similar to 28 GPa. The first high pressure phase transformation to the fergusonite structure (space group I2/a) is found to be of thermodynamically second order. The second high pressure phase could be fitted to the P2/c space group, but detailed analysis rules out the wolframite structure (P2/c space group), common to many scheelite compounds under high pressures. We also suggest that despite the ionic character of the LiF4 tetrahedra, the compressibility of LnLiF(4) (Ln=Eu-Lu) kind of scheelites is more affected by the LnF(8) dodecahedra than the LiF4 tetrahedra. (C) 2015 Elsevier Inc. All rights reserved.