It should also be noted that structure C in Figure Comparing our simulations to the experimental solid-state NMR spectra for the samples with compositions of x = 0.5 and x = 0.75 may corroborate the mechanisms at play. Therefore, first, the number and nature of Na sites present in these two samples were extracted from 2D Na MQMAS NMR experiments (Figure ; Table ), where the signals are separated according to their isotropic chemical shift in the indirect dimension (y axis), while the direct dimension contains both, the chemical shift and the quadrupolar interaction. The MQMAS spectra show the signals for Na in typical Na1 (5 ppm) and Na2 (0.4 ppm) environments from NZC with small quadrupolar couplings (< 0.7 MHz).