The typical energy above the convex hull (Eₐₕ) for metastable phases varies depending on the type of material and its chemistry. However, general trends have been observed in computational materials databases like the Materials Project and high-throughput DFT studies:

General Trends for Metastable Phases:

- Highly metastable phases: > 0.2–0.3 eV/atom → Usually unstable, unlikely to be synthesized unless under extreme conditions (high pressure, temperature, or specific kinetic trapping).

- Moderately metastable phases: 0.1–0.2 eV/atom → Can sometimes be stabilized under specific conditions (e.g., thin films, nanostructures, or entropic stabilization at high temperatures).

- Low metastability (likely synthesizable phases): 0.05–0.1 eV/atom → Often observed experimentally, particularly in oxides, sulfides, and intermetallics.

- Near-stable phases: < 0.05 eV/atom → Frequently found in nature or easily synthesized in bulk.

Material-Specific Considerations: - Oxides & Fluorides: Tend to tolerate slightly higher metastability (~0.1–0.2 eV/atom) due to entropy stabilization and kinetic trapping. - Nitrides & Carbides: Often require lower energy above hull (< 0.1 eV/atom) for stability. - Metals & Alloys: Typically require Eₐₕ < 0.05 eV/atom to be experimentally observed. - Battery Materials: Many metastable cathode materials (e.g., Li-rich layered oxides) show 0.1–0.15 eV/atom above hull but can still be synthesized.