Dear Leong Sim

Freezing the CoPi/ metal oxide in N2, depends on its structure. If it is a non-homogeneous composite or a thin film on substrata you have to be careful about sample cracking during cooling.

There being no Pi in the Periodic Table, do you mean the polymer polyimide? If so, you have a rather complicated stack of a rather hard but tensile metal, a soft polymer and a tough ceramic oxide of which it may be difficult to prepare a good cross-section for SEM or TEM. I suggest you try cutting of the cooled stack by an ultramicrotome with diamond knife (which risks debonding and breakage) and compare this with room temperature cutting after wax embedding using a diamond coated wire saw with very little pressure (which risks deformation of the soft material).