NbNx

NbNx refers to a family of niobium-nitrogen compounds in which the nitrogen content is non-stoichiometric, described by the formula NbN_x. The value of x is close to unity but can deviate due to synthesis conditions, leading to nitrogen vacancies or interstitials. These materials are part of the broader class of transition-metal nitrides, known for hardness, chemical stability, and metallic conductivity.

NbN commonly crystallizes in the rocksalt (face-centered cubic) structure; nonstoichiometry introduces point defects without necessarily destroying the overall lattice. Defect concentration influences properties such as elastic moduli, resistivity, and superconducting behavior.

NbN and NbN_x are typically prepared by reactive sputtering of niobium in a nitrogen-containing atmosphere, chemical vapor deposition, or high-temperature solid-state reactions. The exact x is determined by nitrogen partial pressure, substrate temperature, and post-deposition annealing, among other processing parameters.

NbN itself is a hard, high-melting-point ceramic with high electrical conductivity and a superconducting transition near 16 K for stoichiometric NbN. Non-stoichiometric NbN_x shows tunable properties; nitrogen vacancies can raise resistivity and alter Tc. NbN_x thin films and coatings are used as protective hard coatings, diffusion barriers in microelectronics, and optical coatings, as well as in superconducting devices such as nanowire single-photon detectors.

Related topics include niobium nitride and other transition-metal nitrides.