Cryoground and mixed powders of the constituents of the material PEO3NaClO4 have been monitored by nuclear magenetic resonance spectroscopy (NMR), and by X-ray techniques, at room temperature and above, to explore the formation of the crystalline complex. The proton, C-13, and Na-23 nuclei are observed. Similar 38:1 and 10:1 initially unreacted powders are also monitored to help in this assignment. The C-13 data on the amorphous fraction shows a monotonic shift with sodium concentration in the amorphous/liquid state at 360 K, giving rise to the possibility of using C-13 shifts as a measure of cation concentration in the amorphous state. The Na-23 and X-ray results indicate that the crystal starts to form at room temperature. At the maximum temperature of the spinning NMR probe (similar to 360 K) the crystal formation is rapid but a residual amount (similar to 5%) of NaClO4 remains undissolved. Interestingly, the initial growth of the 'sodium in polymer' NMR spectral intensity follows a similar pattern in all three samples monitored, 3:1, 10:1, and 38:1, indicating that the 3:1 complex is a preferred form for sodium perchlorate in polyethylene oxide (PEO).