  We have measured the electrical resistance of micrometric to nanometric
powders of the La$_{5/8-y}$Pr$_y$Ca$_{3/8}$MnO$_3$ (LPCMO with y=0.3) manganite
for hydrostatic pressures up to 4 kbar. By applying different final thermal
treatments to samples synthesized by a microwave assisted denitration process,
we obtained two particular grain characteristic dimensions (40 nm and 1000 nm)
which allowed us to analyze the grain size sensitivity of the electrical
conduction properties of both the metal electrode interface with manganite (Pt
/ LPCMO) as well as the intrinsic intergranular interfaces formed by the LPCMO
powder, conglomerate under the only effect of external pressure. We also
analyzed the effects of pressure on the phase diagram of these powders. Our
results indicate that different magnetic phases coexist at low temperatures and
that the electrical transport properties are related to the intrinsic
interfaces, as we observe evidences of a granular behavior and an electronic
transport dominated by the Space Charge limited Current mechanism.
