THERMOPOWER AND RESISTIVITY MEASUREMENTS ON OXYGEN-ANNEALED HGBA2CACU2O6+DELTA

We have measured the thermoelectric power and resistivity of the 120 K superconductor HgBa2CaCu2O6+delta (Hg-1212) as a function of temperat ure and oxygen annealing. Before annealing the Seebeck coefficient is moderate and positive, suggesting that the as-grown compound is slight ly under-doped. After annealing in oxygen at 200-degrees-C for 10 h, T (c) was enhanced by 5 K. Further annealing increased T(c) by an additi onal 1 K and sharpened the transition. The thermopower shifts downward with increasing doping by oxygen annealing, resembling that of the Bi -based and Tl-based systems. The carrier concentration was estimated f rom thermopower data and the T(c) value as approximately 0.13 and appr oximately 0.14 per Cu before and after oxygen annealing, respectively.