Storage-oriented applications, such as embedded memories, require PCMs with higher amorphous-phase stability at (very) high temperature. The computing and energy efficiencies of phase-change neuro-inspired computing are expected to be further improved using this new heterostructure alloy 22. 21, it was shown how this issue can be resolved: by the design of a heterostructure that confines amorphous Sb 2Te 3 nanolayers between robust non-PCM TiTe 2 crystalline nanolayers, enabling memory operation with nine accurate resistance states. For high-performance neuro-inspired computing, the spontaneous structural relaxation of amorphous GST is the major obstacle, causing the well-known issue of resistance drift 20. The stability of amorphous Sb 2Te 3 thin films can also be improved by alloying with Sc, leading to a T x of about 150 ☌-due to an increase in viscosity, and thus a decrease in growth rate, at low temperatures 10, 11, 12. The recently designed Sc 0.2Sb 2Te 3 (SST) alloy brings the programming time down to ~0.7 ns, expanding the capability of PRAM for cache-type memory applications 10, 11, 12, 13, 14, 15. Ab initio materials screening studies have recently shown that alloying with a suitable element, such as Sc 10, 11, 12, 13, 14, 15 or Y 16, 17, 18, 19, can largely increase the nucleation rate to improve switching speed at elevated temperatures. Moving towards the Sb 2Te 3 end of the compositional pseudo-binary line, the switching speed is further improved, but the amorphous-phase stability is weakened, with a T x as low as 85 ☌ 9. For a given artificial intelligence (AI) computing task, such as pattern classification, Ge 2Sb 2Te 5 based memory arrays were shown to improve the computing, energy, and areal efficiencies by one to two orders of magnitude compared to current computing hardware 7, 8. Neuro-inspired computing utilizes the multilevel storage capability of Ge 2Sb 2Te 5, making it possible to process data directly within the memory arrays. As-deposited Ge 2Sb 2Te 5 thin films show a crystallization temperature T x of ~150 ☌, and a minimum switching time of ~10 ns in state-of-the-art devices 5, 6. The core material in use is the Ge 2Sb 2Te 5 alloy, located at the midpoint of the GeTe–Sb 2Te 3 pseudo-binary line 4. Competitive storage-class memory products based on PCMs-known as 3D Xpoint-have entered the global memory market recently, largely boosting computing efficiencies by bridging the performance gap between dynamic random access memory (DRAM) and flash-memory-based solid state hard drives (SSD). Phase-change random access memory (PRAM) is programmed to switch between the amorphous and crystalline states of PCMs reversibly and rapidly, and the pronounced contrast in electrical resistance (over three orders of magnitude) or optical reflectance (over 30%) between the two states is used to encode data 1, 2, 3. Chalcogenide phase-change materials (PCMs) are leading candidates to implement these functionalities. With increasing global demand for data storage and processing, massive efforts are underway to develop new electronic devices and platforms, including non-volatile memory and neuro-inspired computing technologies 1, 2, 3. Based on the acquired knowledge at the atomic scale, we provide a materials design strategy for high-performance embedded phase-change memories with balanced speed and stability, as well as potentially good cycling capability. Together with energetic analyses, a compositional threshold is identified for the viability of a homogeneous amorphous phase (‘zero bit’), which is required for memory applications. Electronic-structure computations and smooth overlap of atomic positions (SOAP) similarity analyses explain the role of excess Ge content in the amorphous phases. Here, we report comprehensive first-principles simulations that give insight into those emerging materials, located on the compositional tie-line between Ge 2Sb 1Te 2 and elemental Ge, allowing for a direct comparison with the established Ge 2Sb 2Te 5 material. Ge–Sb–Te alloys with higher Ge content, most prominently Ge 2Sb 1Te 2 (‘212’), have been studied as suitable alternatives, but their atomic structures and structure–property relationships have remained widely unexplored. However widely used, this composition is not suitable for embedded memories-for example, for automotive applications, which require very high working temperatures above 300 ☌. The Ge 2Sb 2Te 5 alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature.