Abstract
Essentially single-phase Hg-1223 and Cu-1223:P samples in wide hole-doping ranges were successfully synthesized by a high-pressure (5 GPa) technique utilizing internal and/or external oxidizing agents and by subsequent post-annealings performed in a thermobalance. The hole-doping level of the as-synthesized samples was found to be in the overdoped side for both of the phases by thermoelectric power measurements. 
values as low as 107 K and 67 K were obtained for the overdoped Hg-1223 and Cu-1223:P samples, respectively. The values of 
and 
were calculated from the measured M versus H data employing, respectively, the Bean model 
and two different criteria: 
(at 
) and (as 
). It was found that the heavier the doped hole concentration was, the more improved were the versus 
characteristics for both the Hg-1223 and the Cu-1223:P phases. This tendency was the same for versus characteristics calculated using either criterion. The improvement with increasing hole-doping level was especially profound in the case of Cu-1223:P: the versus characteristics of a Cu-1223:P sample with 
K, probably being close to the optimally doped state, were as poor as that reported for Bi-2212, while an overdoped Cu-1223:P sample with 
K was superior to an overdoped Hg-1223 sample with 
K. The mechanisms as well as the usefulness of the observed phenomena are discussed.
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