## 1 Introduction
Many other systems such as Ga-Ge-Sb-S [37], Ge-Sb-S [35; 38], and Ge-Ga-S [39; 40], have also been explored, in which thermo-mechanical properties have been improved by the addition of an alkali halide. However, in the case of adding halides to the base glass composition, the improvement of such properties can come at the expense of chemical stability. In this study, we have focused on the measurement of the glass and GC's micro-indentation response as quantified by Vickers hardness, and a variation in the materials Young's modulus following heat-treatment. A multicomponent ChG is the subject of the study, GeSe\({}_{2}\)-As\({}_{2}\)Se\({}_{3}\)-PbSe (GAP-Se), which possesses good transparency in the IR region and exhibits the requisite narrow size distribution of the secondary crystallized phase(s) making it suitable as an optical nanocomposite [23; 35; 41]. Such behavior enables the use of a controlled crystallization protocol to realize high RI nanocrystals for GRIN applications. This system has been widely explored in the field of non-selective as well as selective micro-crystallizations in both bulk and thin films. Compared to the sulfide based of GeS\({}_{2}\)-As\({}_{2}\)S\({}_{3}\)-PbS system [7; 42], the Se-based glass shows transmission further into the IR region, and exhibits better chemical stability. Further examination of glasses containing 10-40 mole% PbSe (maintaining a 1:3 ratio of GeSe\({}_{2}\) to As\({}_{2}\)Se\({}_{3}\)) [6; 42] clearly showed liquid-liquid phase separation (PS) via transmission electron microscopy (TEM). The composition of these immiscible amorphous phases and their respective crystalline stability has been shown to impact where crystallization initiates and then extends. For example, in the 20 mole% PbSe [20 PbSe] glass, the secondary droplet phase was Pb-rich, round and uniform in composition with lower crystallization stability, surrounded by a Pb-deficient matrix. In the 30 mole% PbSe composition, the secondary phase remained Pb-rich, but their shape was elongated. Conversely, in the 40 mole% PbSe composition, the matrix became Pb-rich, and the secondary phase was Pb deficient [42]. Thus, one would expect due to the variation in composition of the Pb-rich droplet or matrix phase, the extent and phase fractions of nanocrystallites formed would vary for a constant thermal crystallization protocol. Indeed, this is what has been previously observed, but the impact of such crystallization on post heat-treatment mechanical properties has not been previously reported. This study examines the impact of crystallization on post heat-treatment mechanical properties, by comparing the phase separated Pb-rich parent glass (PSPG) to a compositionally identical, albeit homogenous and droplet-free parent glass (DFPG). While phase separation is intrinsically driven by thermodynamics, several methods (control of batch/melt size, quench rate, heating protocols), have been shown in some compositions to alleviate phase separation in this glass system. However, in our efforts to prepare the above GAP-Se composition, none of these changes have resulted in a non-phase separated material when prepared from a melt/quench process. Recently, in collaboration with our commercial partners Amorphous Materials, Inc., (AMI) and their outside materials engineering consultant, a novel glass preparation process provided us with our first droplet free 20 mole% PbSe composition in a high-volume quantity melt (>2 Kg). This DFPG was prepared by leveraging AMI's proprietary chalcogenide glass manufacturing process with a computer-controlled furnace system, providing a pathway to evaporate the chemicals homogenously under high vacuum and condense instantaneously, as a target. In this paper, our key objective has been to compare property variation attributable to this variation in morphology (phase separation of small, conventionally lab melt material versus homogeneous commercial melt morphology).