PREPARATION OF SUPERCONDUCTING YBA2CU3O7-DELTA FROM CARBON-FREE PRECURSORS

Iodates of yttrium, barium and copper have been studied as possible ca rbon-free starting materials for the superconducting YBa2Cu3O7-delta c ompound. TG and EGA experiments on the individual iodates show that wh ile the copper and yttrium iodates readily decompose to oxides, the de composition of Ba(IO3)2 to BaO is incomplete up to 1050-degrees-C owin g to the thermal stability of Ba5(IO6)2. However, when a three-compone nt, mechanical mixture is heated in flowing air a complete reaction oc curs by 900-degrees-C, yielding the YBa2Cu3O7-delta phase. A coprecipi tation method to produce the starting material was studied as well but found difficult to optimize owing to different solubilities and possi ble double iodate formation. The resulting products were characterized by XRD for phase purity and crystallinity, by TG for oxygen release a nd uptake behaviour as well as by resistivity measurements for superco nducting properties.