Studies of Inner-~Shell Chemistry of Mercury Based Compounds at Extreme Conditions
Abstract
It has been theoretically predicted that when mercury difluoride (HgF2) is pressurized to above 50 GPa in the presence of molecular fluorine, it will most likely transform into mercury tetrafluoride (HgF4), thus mercury will behave as a transition element at high pressure. However, there is no experimental evidence verifying this prediction yet. To begin with, the crystalline properties of pure HgF2 at high pressure were not experimentally established. In this thesis, the high pressure structural properties of HgF2 are investigated by means of synchrotron X-ray powder diffraction. Our results reveal that the predicted, ambient cubic structure of HgF2 with the space group Fm3m, can be obtained via a high-pressure ramp purification process using powdered HgF2 mixed with crystalline XeF2 which serves as our molecular fluorine source. The structural transformation of purified HgF2 is observed above 2.5 GPa, and by using first-principle calculations, two candidate structures with space groups Pnma and Pnam are proposed which persist up to 63 GPa. Furthermore, studies of HgF2 in the presence of F2 produced by the X-ray induced decomposition of XeF2 up to 70 GPa are reviewed. The obtained results provide more insights into the highpressure behavior of mercury-fluorine compounds and will benefit further experimental investigation of high pressure induced synthesis of HgF4.