Nitrogen-doped niobium for SRF cavities

Niobium is the standard material for superconducting RF (SRF) cavities. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram the cubic δ-phase of NbN has the highest critical temperature (16 K). Niobium samples were N-doped at the refurbished UHV furnace at IKP Darmstadt. In parallel, reference samples were annealed in 1 bar nitrogen atmosphere at different temperatures in a tube furnace. In this contribution we focus on the structural investigations (X-ray diffraction and pole figure, secondary ion mass spectroscopy, scanning electron microscopy) of the doped samples.