PRESSURE-INDUCED PHASE-TRANSFORMATION IN ZRW2O8 - COMPRESSIBILITY ANDTHERMAL-EXPANSION OF THE ORTHORHOMBIC PHASE

In situ neutron powder diffraction has been used to show that the appl ication of hydrostatic pressure at room temperature produces a transfo rmation of ZrW2O8 from the cubic to an orthorhombic phase beginning at 2.1 kbar and completed by 3.1 kbar, with a 5% reduction in volume. Af ter release of pressure, the orthorhombic phase is retained at room te mperature. Its thermal expansion is negative below room temperature, b ut is positive above room temperature with a transformation back to th e cubic phase at about 390 K. The WO4 groups are found to play the dom inant role in both phase transformations. The volume compressibilities of the cubic and orthorhombic phases are 1.38 x 10(-3) and 1.53 x 10( -3) kbar(-1). respectively. (C) 1998 Published by Elsevier Science B.V . All rights reserved.