The correlation between microstructure, superconducting properties and proc
essing has been investigated with Hg1-xTlxBa2CuO4+y powders. These samples
exhibit poor shielding and field-induced dissipation, as commonly found in
other Hg-based cuprates. In addition, grains typically present a high densi
ty of low-angle grain boundaries; these are likely to be related to the syn
thesis technique and appear responsible for the field-induced granular beha
viour.