Effects of pressure on the local atomic structure of CaWO4 and YLiF4:: mechanism of the scheelite-to-wolframite and scheelite-to-fergusonite transitions

The pressure response of the scheelite phase of CaWO4 (YLiF4) and the occurrence of the pressure-induced scheelite-to-wolframite (M-fergusonite) transition are reviewed and discussed. It is shown that the change of the axial parameters under compression is related to the different pressure dependences of the W-O (Li-F) and Ca-O (Y-F) interatomic bonds. Phase transition mechanisms for both compounds are proposed. Furthermore, a systematic study of the phase transition in 16 different scheelite ABX(4) compounds indicates that the transition pressure increases as the packing ratio of the anionic BX4 units around the A cations increases. (C) 2003 Elsevier Inc. All rights reserved.