Niobium and niobium-titanium nitrides for RF applications

The work deals with the study of the application of niobium and niobium-titanium nitrides in RF devices. Nitride samples, prepared by diffusion of nitrogen in bulk niobium and alloy, have been characterized by X-ray diffraction. SEM and AC magnetic measurements. Several phases of niobium nitride have been observed: the phase with higher nitrogen content, at the sample surface, has critical temperature about 15 K but inclusions of both lower Tc and not superconducting phases enhance the RF surface resistance. The surface of niobium-titanium nitride is composed by a phase having critical temperature up to 17 K and unwanted phases were not observed.