Synthesis and Characterization of a Niobium Nitride Precursor and Niobium Nitride Powder
نویسندگان
چکیده
Anodic dissolution of Nb foil in an electrolyte solution containing liquid NH3 and NH4Br produces an insoluble precursor that can be calcined to yield phase-pure NbN. Infrared spectroscopy is consistent with a precursor having the general formula NbXn(NH2)5-npNH3. By changing the calcination conditions, the phase of the resulting NbN powder can be varied. For example, calcining in pure Ar yields the superconducting 6-NbN phase a t 600 and 800 "C but results in Y-NbN a t 1000 "C. A mixed 85 % Ad15 % H2 calcining atmosphere also results in 6-NbN a t 600 "C, but yields y N b N phases a t 800 OC. When the precursor powder is calcined in NH3 a t 600, 800, or 1100 "C y N b N phases result, but subsequent calcining in Ar at 1450 "C yields superconducting 6-NbN (T, = 14.75 K). The calcination ambient affects the chemical composition of the powder: in all cases more reducing conditions lower the level of Br contamination.
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