  We report the effect of Mn site substitution of Al on the structural,
magnetic and transport properties of charge ordered Pr{_0.5}Ca{_0.5}MnO{_3}.
This substitution introduces impurities in the Mn-O-Mn network, causes the
Mn{^3+}/Mn{^4+} ratio to deviate away from unity and is seen to predominantly
replace Mn{^4+}. The strength of charge ordering is supressed with increasing
Al doping, as is seen from ac susceptibility, the magnetocaloric effect and dc
resistivity. The observation of traces of charge ordering over an extended
range of impurity doping of 10% besides being indicative of the robust nature
of charge ordering in Pr{_0.5}Ca{_0.5}MnO{_3}, also underscores the relatively
insignificant effect that Al substitution has on the lattice distortions and
the importance of non-magnetic substitutions. For all the samples, the
conductivity in the temperature range above the charge ordering transition is
observed to be due to the adiabatic hopping of small polarons, whereas below
the charge ordering transition, Mott's variable range hopping mechanism is seen
to be valid.
