Intermediate phase formation during Hg-2212 synthesis by in-situ X-ray synchrotron diffraction

The synthesis of Hg2Ba2YCu2O8-delta (Hg-2212) requires a high pressure - high temperature process. The determination of the reaction path is an important piece of information for its optimization. In-situ X-ray diffraction at high pressure-high temperature has been performed tot monitor this process by using the synchrotron source of ESRF (Grenoble-France, ID30 beam line). The synthesis was followed at 4 GPa from room temperature to 850 degreesC. When the starting powder is a mixture of oxides (BaO2, YzO(3), CuO) and Cu, a transient oxide phase composed at least of Pa and Hg is formed that is then converted into the final Hg-2212 product. Conversely no intermediate phase can be detected when a pre-reacted precursor "Ba(2)YCu(2)Oy" mixed with HgO is used.