Upon closely examining the Seebeck behaviour of Hg-1201 we have discovered that the system, whether stoichiometric or mercury deficient, appears to behave in similar fashion to the LBCO and YBCO-123 systems in that a dip appears in Tc
( p
) at p
~1/8. We have earlier indicated that this concentration of holes marks the point at which stripe phase formation in the organization of charge and spin in the two-subsystem, mixed-valent, HTSC materials passes from one charge wall loading scheme to another.
We observe a strong difference in doping characteristics between the mercury-deficient and mercury-stoichiometric systems, and assemble here a plausible scenario of what is involved. While HgBa2
CuO4+
indeed does offer very considerable potential advantages as an archetype to the cuprate HTSC phenomenon, excess anion systems like this clearly introduce materials complexities. These will always demand careful attention and perhaps not endear the system to many accustomed to the relative simplicities of a cation-doped system.