In thin film technology, amorphous Al2O3 ─ based coatings are well known for their high temperature stability, oxidation and corrosion resistance, combined with electrical and optical properties, leading to a broad field of possible applications. However, technically requested durability in thermal loading and harsh environments induces the request for prolonging the integrity of the as-deposited structures, by impeding phase transitions to a crystalline state. While literature experimentally demonstrated this may be achieved via alloying with Si [1], current theoretical understanding is lacking. Therefore, this study seeks to fill the existing knowledge gap by connecting experimental analysis of PVD-synthesized thin films by the means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD)-based annealing experiments with density functional theory (DFT) simulations. The latter compromises an analysis of chemical stability of amorphous and crystalline phases in the Al2O3 rich region of the Al-Si-O phase diagram. This is combined with an in-depth analysis of short and medium range order, chemical bonding, network vibrations, and void-mediated hopping events of the amorphous (Al,Si)2O3 phase. An insignificant impact of the hopping barrier energy, alongside a distinct reduction in hopping attempts mediated through Si alloying can be stated as main findings of the present study. [1] Bolvardi H, et al., J Appl Phys 2015;117:025302.