Electrochemical synthesis of ceramic materials. 3. Synthesis and characterization of a niobium nitride precursor and niobium nitride powder

• Published in: Chemistry of materials Vol. 6; no. 1; pp. 87 - 92
• Main Authors: Wade, Travis, Crooks, Richard M, Garza, Ernest Gene, Smith, Douglas M, Willis, Jeffrey O, Coulter, J. Yates
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.01.1994
• Subjects: CERAMICS; CHEMICAL PREPARATION; MATERIALS SCIENCE; NIOBIUM COMPOUNDS; NIOBIUM NITRIDES; NITRIDES; NITROGEN COMPOUNDS; PNICTIDES; REFRACTORY METAL COMPOUNDS; SUPERCONDUCTORS; SYNTHESIS; TRANSITION ELEMENT COMPOUNDS 360201 > Ceramics, Cermets, & Refractories > Preparation & Fabrication
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm00037a019

Anodic dissolution of Nb foil in an electrolyte solution containing liquid NH[sub 3] and NH[sub 4]Br produces an insoluble precursor that can be calcined to yield phase-pure NbN. Infrared spectroscopy is consistent with a precursor having the general formula NbX[sub n](NH[sub 2])[sub 5-n][center dot]pNH[sub 3]. By changing the calcination conditions, the phase of the resulting NbN powder can be varied. For example, calcining in pure Ar yields the superconducting [delta]-NbN phase at 600 and 800 [degrees]C but results in [gamma]-NbN at 1000 [degrees]C. A mixed 85% Ar/15% H[sub 2] calcining atmosphere also results in [delta]-NbN at 600 [degrees]C, but yields [gamma]-NbN phases at 800 [degrees]C. When the precursor powder is calcined in NH[sub 3] at 600, 800, or 1100 [degrees]C [approximately]-NbN phases result, but subsequent calcining in Ar at 1450 [degrees]C yields superconducting [delta]-NbN (Tc = 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. 42 refs., 8 figs., 1 tab.