  We observe how the charge-ordering (CO) temperature of Nd1/2Sr1/2MnO3
decreases with the external pressure p from 160 K at p = 0 down to 30 K at p ~
4.5 GPa, by measuring the values p, T where the far-infrared spectral weight of
the metallic phase is fully recovered. We thus determine the (p, T) phase
diagram of CO in that manganite. We also find that the parameter d(lnTCO)/dp
which describes this metallization from the CO phase is equal and opposite to
the quantity d(lnTc)/dp which governs the metallization of the paramagnetic
state at comparable Curie temperatures Tc, in similar manganites at half
doping.
