  Yttria stabilized Zirconia (YSZ) pellets with different crystallite sizes
were irradiated with 80 MeV Ag$^{6+}$ ions at room temperature and 1000 K to
understand the role of crystallite size/material microstructure and irradiation
temperature on the radiation tolerance against high electronic energy loss
(S$_e$). X-ray diffraction and Raman spectroscopy measurements reveal that,
irrespective of the irradiation temperature, the nano-crystalline samples
suffered more damage as compared to the bulk-like sample. A reduction in the
irradiation damage i.e. improvement in the radiation tolerance, was observed
for all the samples irradiated at 1000 K. The reduction in the damage, however,
was remarkably higher for the two nano-crystalline samples compared to the
bulk-like sample, and hence the difference in the damage between the bulk-like
and nano-crystalline samples was also significantly lower at 1000 K than that
at room temperature. The irradiation damage, against S$_e$, was thus found to
be critically dependent on the interplay between the irradiation temperature
and crystallite size. These results are explained with the help of detailed
theoretical calculations/simulations based on the 'in-elastic thermal spike'
model by taking into consideration the combined effect of crystallite size and
environmental (irradiation) temperature on the electron-phonon coupling factor
and lattice thermal conductivity (and hence on the resulting thermal spike).
Our results are crucial from the fundamental perspective of comprehending the
size and temperature dependent radiation damage against S$_e$ ; and also for a
number of applications, in various radiation environments, where nano-materials
are being envisioned for use.
