Microwave surface resistance of YBCO bulk samples prepared by addition of HgO to YBCO system

The paper reports microwave surface resistance (R/sub s/) measurement on yttrium barium copper oxide (YBCO) bulk samples, prepared by an alternate route, namely by addition of mercury oxide (HgO) to YBCO system. R/sub s/ is measured using a TE/sub 011/ mode cylindrical cavity, at 20 GHz, by the end plate substitution technique. HgO added to the YBCO system has the advantage that oxygen in HgO acts as a copious source of oxygen and therefore does not require sintering in oxygen flow. Powder X-ray diffraction studies confirm the formation of pure orthorhombic 123 phase without any indication of Hg or known Hg compounds. The specimen with 0.5 wt.% of HgO added to the YBCO system showed superior superconducting properties including microwave surface resistance (22.5 m/spl Omega/ at 77 K and 20.0014 GHz). The R/sub s/ has also been measured as a function of the area of the sample that yields consistent value confirming surface homogeneity. This is believed due to stoichiometric oxygenation and large number of well connected grains.