The peaks of all the alloys are visibly broader than the pure Sn and Ti compositions, with Cs 2 TiX 6 having larger full-width half-maximums (FWHMs) than Cs 2 SnX 6 . We believe that the different peak broadening in the diffraction pattern of the samples originate from the characteristic strain that the crystal lattice undergoes in NCs with different sizes and compositions. Indeed, the shape and size distribution of the NCs varied significantly with the composition, with, for instance, Cs 2 SnI 6 showing a narrower size distribution and more symmetrical shapes than the mixed compositions and Cs 2 TiI 6 (Figures and), which would explain the narrower FWHM witnessed for Cs 2 SnI 6 . The strain has an effect not only on the width of the peaks but also on their position, which could therefore not be used to calculate the percentage of Sn using Vegard's law.