Microstructural factors influencing the properties of high surface area molybdenum nitride films converted from molybden
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Microstructural factors influencing the properties of high surface area molybdenum nitride films converted from molybdenum trioxide films deposited via solution spray pyrolysis S. L. Robersona),b) Department of Materials Science and Engineering, North Carolina State University, Box 7907, Raleigh, North Carolina 27695-7907
D. Finello U.S. Air Force Research Labs, Munitions Directorate, Eglin AFB, Florida 32542-6810
R. F. Davis Department of Materials Science and Engineering, North Carolina State University, Box 7907, Raleigh, North Carolina 27695-7907 (Received 20 August 1997; accepted 11 December 1997)
Molybdenum trioxide (MoO3 ) films, 15 mm thick, have been deposited on 50 mm thick polycrystalline titanium substrates from 250 to 500 ±C via liquid spray pyrolysis. Molybdenum pentachloride (MoCl5 ) dissolved in methanol was used as the molybdenum source; ambient conditions provided the oxygen source. X-ray diffraction (XRD) data indicated that amorphous MoO3 films were produced at deposition temperatures below 400 ±C. Randomly orientated polycrystalline MoO3 films were produced at 400 ±C and higher deposition temperatures. The deposition temperature also influenced the surface area of the films and their average grain size. Subsequent conversion of the MoO3 films to high surface area (HSA) conductive films containing both g –Mo2 N and d –MoN was accomplished via programmed reactions with anhydrous NH3 and involved the formation of MoO2 and MoOx N12x as intermediate phases. The degree of crystallinity, surface area, and average grain size of the MoO3 films strongly influenced the average grain size and surface area of the resultant Mox N films.
I. INTRODUCTION
Molybdenum trioxide (MoO3 ) has recently been investigated for its numerous potential applications as catalysts for the petroleum, chemical, and pollution control industries,1–8 its electrochromic properties,9–11 and as a precursor for the preparation of high surface area (HSA) powders of molybdenum carbide and nitride.12–19 This last use is of interest to the present investigators because the conversion of MoO3 to Mox N (consisting of both d –MoN and g –Mo2 N) results in marked increases in both surface area and electrical conductivity. The achievement of the combination of high surface area (.30 m2yg) and electrical conductivity (1yr 104 ohm21 cm21 ) in films of Mox N would make them candidate electrodes for high energy density double layer capacitor storage devices. The preparation of Mox N powders from the conversion of MoO3 in NH3 has been a)
Correspondence concerning this paper should be directed to S. L. Roberson at U.S. Air Force Research Labs, Munitions Directorate, Bldg 432 Fuzes Branch, 306 W. Eglin Blvd, Eglin AFB, Florida 32542-6810. b) U.S. Air Force Palace Knight student at North Carolina State University. J. Mater. Res., Vol. 13, No. 8, Aug 1998
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extensively studied; however, the conversion of MoO3 films to Mox N has not been investigate
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