DEPENDENCE OF T-C AND TRANSPORT-PROPERTIES ON THE CU VALENCE IN HGBA(2)CA(N-1)CU(N)O2((N+1)+DELTA) (N=2,3) SUPERCONDUCTORSO

We have determined the oxygen content and the Cu valence by iodometric titiration of single-phase HgBa2Can-1CunO2O2(n+1+delta) (n=2,3), Hg-1 212 and Hg-1223 superconductors postannealed under various conditions in either a reducing or an oxidizing atmosphere. Their lattice paramet ers, T-c, resistivity, and the thermoelectric power have been systemat ically investigated as a function of Ca valence. Hg-1212 exhibits a pa rabolic or ''bell-shaped'' relationship between T-c and the Cu valence similar to that reported for HgBa2CuO4+delta (Hg-1201), while only a half of the parabola is observed for Hg-1223. The systematic variation s in the resistivity and the thermoelectric power as well as the relat ionship between T-c and the Cu valence confirm that the Hg-1223 sample with the highest T-c of 135 K is almost optimally doped. Both Hg-1212 and Hg-1223 as well as Hg-1201 exhibit their maximum T-c values at th e same nominal Cu valence of approximately 2.20 which is also comparab le to those for other high-T-c cuprate superconductors. This coinciden ce of the Cu valence for optimally doped states suggests that the simp le ionic model where each excess oxygen in the Hg-O-delta charge reser voir supplies two holes is appropriate in the present Hg-12(n-1)n samp les.