## 3 Results and Discussion
Although, all the above-mentioned crystalline peaks were present in both the melts, the Pb-rich crystallites were the preferred crystallites in the lab melt, whereas As\({}_{2}\)Se\({}_{3}\) was the principal crystalline phase in the commercial melt. This is the key difference that substantiates our assumption of the role of glass constituent's physical dispersion within the parent glass matrix, and how that dispersion impacts which crystal phase dominates the post-heat-treated GC's microstructure. As noted below, this variation impacts the resulting GC's mechanical properties. What is important for our understanding is that, despite using the same heat-treatment protocol, the type and rate of formation of secondary crystalline phases was different, which supports the fact that the base glass morphology is the limiting factor in the formation of GCs. Figure 4c,d illustrates the average crystal size and size distribution of the As\({}_{2}\)Se\({}_{3}\), as well as PbSe crystals formation in the commercial and lab melt during the stepwise heat-treatment protocol, respectively, depicted in the series of steps shown in the XRD data. The average size and the size distribution of the crystals were measured on SEM images of the heat-treated samples, using ImageJ software to distinguish between different crystal phases. The average size of the PbSe crystals in the lab melt sample is \(\sim\)2.96x (lab melt = 267.89 \(\pm\) 20.34 nm, commercial melt = 90.93 \(\pm\) 21.16 nm) of the average PbSe crystal in commercial melt for the same heat-treatment conditions (temp/times), while the As\({}_{2}\)Se\({}_{3}\) crystal size in commercial melt is \(\sim\)1.72x (lab melt = 91.56 \(\pm\) 16.89 nm, commercial melt = 157.93 \(\pm\) 24.56 nm) that of lab melt under the same conditions. The large error bars for the data are due to the error in manually measuring the crystallite size in ImageJ software, which relies on visual estimation. This variation in crystal size and (apparent) growth rates between the two materials might be expected, as the Pb-containing phases in the lab melt are isolated in the droplets of the phase separated glass and not in the homogeneous plate where all four glass constituents are uniformly spatially dispersed. Here, the thermal energy during the nucleation and growth goes to crystallize the more (prone to crystallization) susceptible phases first, that being the PbSe-containing crystallites. In the homogeneous plate, there is little activation energy barrier difference, which results in crystallization of As\({}_{2}\)Se\({}_{3}\) phase first, followed by crystallization at high temperature for Pb-rich phases. The difference in the average crystal size also gives us an indication about the preferred crystal phase in-between the two glasses as the phase that nucleates (forms) first, starts growing first, and thus, for a fixed time, would be larger in size. Figure 4e shows the variation in the size distribution of the As\({}_{2}\)Se\({}_{3}\) and PbSe crystals phases in the two glasses based on exposure to the same heat-treatment protocol. In the commercial melt, the As\({}_{2}\)Se\({}_{3}\) is present across the sample, whereas in the lab melt, the PbSe-containing crystal phase(s) are predominant. Therefore, the commercial melt with the overlaid growth and nucleation curve (homogeneous plate) has a broader size distribution of As\({}_{2}\)Se\({}_{3}\) crystals as nucleation and growth of this dominant phase is believed to be occurring concurrently. The onset of formation and growth of Pb-containing phases is seen to occur earlier and faster in the droplet containing phase-separated material, resulting in a broader size distribution in the lab melt samples as compared to that of the commercial melt. How this microstructure evolution translates to changes in mechanical properties of the resulting GC is the primary thesis of this work. Hence, these crystallites and their ability to impart changes to crack formation and propagation, will depend on their type and quantity throughout the residual glass matrix.