PRESSURE-INDUCED PHASE-TRANSITIONS IN CDMOO4 - AN IN-SITU HIGH-PRESSURE X-RAY-DIFFRACTION STUDY UP TO 52 GPA

An in-situ high pressure X-ray diffraction study on CdMoO4 has been ca rried out in the diamond anvil cell up to 52 GPa at room temperature. From the high pressure diffraction data we find two pressure-induced p hase transitions, one near 12 GPa and another near 25 GPa. The first t ransition is from scheelite (tetragonal) to wolframite-type structure (monoclinic) and the second transition is also to a monoclinic lattice , related to the BaWO4-II structure. There is no significant change in the molar volume at the first transition, while at the second transit ion the volume decreases by about similar to 12%. We conclude that the latter is due to change in the Mo-O coordination to truly octahedral coordination. The above results are consistent with the conclusions of a recent high pressure Raman study.