Hafnium (Hf) is a metal with a high melting point and good thermal stability, making it a potential substrate material for certain high-temperature applications. Hf is a good thermal conductor, making it suitable for use in heat-sinking applications. Additionally, hafnium is a relatively low-expansion metal, making it attractive for use as a substrate in applications that require dimensional stability. However, hafnium is not commonly used as a substrate material due to its rarity, high cost, and poor electrical conductivity.