Thermal Expansion of Incompressible US-Type NbN Synthesized in a Diamond Anvil Cell.

A novel niobium nitride, US-type NbN, has been successfully synthesized by nitridation of δ-NbN above approximately 30 GPa in a laser-heated diamond anvil cell. NbN crystallizes in the same orthorhombic structure (space group: ) as η-TaN. NbN consists of regular-shaped polyhedra, and the bulk modulus has been determined to = 300(2) GPa. The low-temperature X-ray diffraction measurements have been successfully conducted for the tiny novel NbN between 297.7(5) and 106.3(3) K under ambient pressure. NbN shows no structural phase transition down to 106.3(3) K, and investigation of the linear thermal expansion coefficients yields α = 3.36(9) × 10 K, α = 5.39(10) × 10 K, α = 6.77(15) × 10 K, respectively. Our study reveals that the incompressible novel nitride shows low thermal expansion behavior, which offers new insights for the development of functional nitrides and their crystal chemistry.