Ternary metal nitrides by the urea route

Article abstract of DOI:10.1016/j.materresbull.2006.08.021

Interstitial molybdenum ternary nitrides, M_nMo₃N (M = Fe and Co, n = 3; M = Ni, n = 2), can be obtained by heating the molybdate precursors, FeMoO₄, CoMoO₄ and NiMoO₄ with urea in the 1:12 molar ratio in the 900-1000 °C range. Fe₃Mo₃N and Co₃Mo₃N are obtained in pure form. The nickel nitride has the composition Ni₂Mo₃N and therefore is in admixture with nickel. All the nitrides have been characterized by various physical methods.

Full text of DOI:10.1016/j.materresbull.2006.08.021

Materials Research Bulletin 42 (2007) 870–874
www.elsevier.com/locate/matresbu
Ternary metal nitrides by the urea route
*
A. Gomathi
Chemistry and Physics Materials Unit and CSIR Centre of Excellence in Chemistry, Jawaharlal Nehru Centre
for Advanced Scientific Research, Jakkur P.O., Bangalore, Karnataka 560 064, India
Received 4 August 2006; received in revised form 17 August 2006; accepted 25 August 2006
Available online 29 September 2006
Abstract
Interstitial molybdenum ternary nitrides, M Mo N (M = Fe and Co, n = 3; M = Ni, n = 2), can be obtained by heating the
n
3
molybdate precursors, FeMoO
Co Mo N are obtained in pure form. The nickel nitride has the composition Ni
the nitrides have been characterized by various physical methods.
2006 Elsevier Ltd. All rights reserved.
4
, CoMoO
4
and NiMoO
4
with urea in the 1:12 molar ratio in the 900–1000 8C range. Fe
3 3
Mo N and
3
3
Mo N and therefore is in admixture with nickel. All
2 3
#
Keywords: A. Nitrides; B. Chemical synthesis
1
. Introduction
Ternary metal nitrides, such as alkaline earth silicon nitrides (MSiN with M = Ba, Sr, Ca), alkaline earth zinc
nitrides (Sr ZnN , Ba ZnN ) and nickel nitrides (Sr NiN and CaNiN) have been synthesized by various means. One
2
2
2
2
2
2
2
of the general procedures involves reacting a transition metal or a main group metal with an alkali or alkaline earth
nitride or amide [1–4]. An approach to synthesize ternary nitrides of the type MWN (M = Fe, Ni, Co) has been to heat
2
the respective ternary oxide precursor in NH [5–7]. The first metallic layered nitride, LiMoN , was synthesized by the
3
2
ammonolysis of either a molecular organometallic precursor or a ternary oxide [8]. Weil and Kumta [9] reported the
synthesis of Fe Mo N, FeWN , Ni Mo N and Ti AlN using complex precursors. Synthesis of Fe Mo N by the
ammonolysis of the oxide precursor has been reported [10]. The ternary nitride, Ni Mo N, has been prepared by
3
3
2
3
3
3
3
3
2
3
heating a metallorganic precursor in NH [11]. Alconchel et al. [12] have reported a study on the influence of
3
preparative variables on the ammonolysis of the molybdate precursors. Both the ammonolysis as well as the plasma
nitridation of FeMoO and CoMoO results in the respective intermetallic nitrides [13]. Synthesis of Fe Mo N and
Co Mo N by mechanochemical alloying and by the nitridation of the corresponding ternary carbide has also been
4
4
3
3
3
3
reported [14]. Prior et al. [15,16] have reported the synthesis of Ni2 M Mo N (M = Co, Pd) and Fe M Mo N
ꢀx
x
3
2ꢀx
x
3
(
M = Ni, Pd, Pt) by heating a stoichiometric mixture of the respective oxides under flowing synthesis gas.
Based on our recent success with the urea route to synthesize binary metal nitrides, such as BN, TiN and NbN [17],
we decided to examine whether this simple procedure can also be used to produce ternary nitrides. In this article, we
report the synthesis of interstitial molybdenum ternary nitrides, M Mo N (M = Fe and Co, n = 3; M = Ni, n = 2) by the
n
3
reaction of the respective ternary metal oxides with urea.
*
Tel.: +91 80 22082825; fax: +91 80 22082760.
E-mail address: gomathi@jncasr.ac.in.
0025-5408/$ – see front matter # 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2006.08.021

A. Gomathi / Materials Research Bulletin 42 (2007) 870–874
871
2
. Experimental
Hydrated metal molybdates were prepared by the dropwise addition of 400 mL (0.25 M) of an aqueous solution of
the metal chloride (FeC1 , CoCl or NiC1 ) to a 150-mL (0.55 M) Na MoO ꢁ(H O) solution, and the solution stirred
2
2
2
2
4
2
2
for 2 h to ensure completion of the reaction. The solid product was isolated by vacuum filtration and rinsed with two
washings of water followed by a washing with ethanol. The solid was air-dried overnight followed by a drying at
1
CoMoO and NiMoO , respectively.
50 8C for 24 h. The products were amorphous and had brown, violet and green colors in the case of FeMoO4,
4
4
To obtain crystalline ternary nitrides, a mixture of the respective oxide precursor and urea in the 1:12 molar ratio
was taken in an alumina boat, placed in quartz tube and heated at 900 8C for 3 h in a N atmosphere and the product
2
quenched to room temperature. When the reaction was performed at 750 8C we obtained the nitrides, but the products
were not completely crystalline.
The products formed in the above reactions were characterized by following techniques. X-ray diffraction (XRD)
patterns were recorded using Cu Ka radiation on a Rich-Siefert XRD-3000-TT diffractometer. Scanning electron
microscope (SEM) images were obtained using a LEICA S440i SEM. M o¨ ssbauer spectra were recorded using a Wissel
5
7
spectrometer. The spectrum was recorded at room temperature using a Co source. The isomer shift is reported
relative to metallic iron at room temperature.
Electrical resistivity of the nitride samples were measured using four probe technique from 50 to 300 K.
3
. Results and discussion
On heating a 1:12 mixture of FeMoO with urea, Fe Mo N with the cubic eta carbide structure was obtained. It
3
4
3
is isostructural with h-Fe W C. The XRD pattern shown in Fig. 1(a) confirms the formation of Fe Mo N
3
3
3
3
˚
(
a = 11.0620 A, JCPDS card no: 48–1408). Fig. 2(a) shows a SEM image of sub-micrometer particles of
Fe Mo N. The M o¨ ssbauer spectrum of Fe Mo N measured at room temperature is shown in Fig. 3. The spectrum
3
3
3
3
ꢀ
1
shows a symmetric single line with an isomer shift of 0.213 mm s characteristic of Fe Mo N as reported in the
3
3
literature [10,18]. The structure of Fe Mo N has iron atoms occupying the sites between the (NMo ) octahedra
3
3
6
which are corner-shared. By heating a 1:12 mixture of CoMoO and urea, we obtained Co Mo N showing a XRD
4
3
3
Fig. 1. XRD patterns of (a) Fe
2
Mo
3
3 3 2 3
N (b) Co Mo N (c) Ni Mo N.

872
A. Gomathi / Materials Research Bulletin 42 (2007) 870–874
2 3 3 3 2 3
Fig. 2. SEM images of (a) Fe Mo N (b) Co Mo N (c) Ni Mo N.
˚
pattern characteristic of cubic eta carbide structure (Fig. 1(b)), with a cell parameter of 11.0134 A [11]. The
product consisted of sub-micrometer sized particles as revealed by the SEM image in Fig. 2(b). The nitride was
metallic as shown by the measurement of the temperature variation of resistivity (Fig. 4). The magnetic
susceptibility data of the two nitrides agree well with literature [10,13] with Co Mo N showing a non-Curie like
3
3

A. Gomathi / Materials Research Bulletin 42 (2007) 870–874
873
Fig. 3. M o¨ ssbauer spectrum of Fe
3 3
Mo N.
3 3
Fig. 4. Variation of resistivity, r, of Co Mo N with temperatures.
and Fe Mo N showing a Curie behavior. The reactions involved in the formation of Fe Mo N and Co Mo N is
3
3
3
3
3
3
likely to be (1):
3
CoMoO4 þ 8NH3 ! Co3Mo3N þ 12H2O þ 7=2N2
(1)
Here, NH is generated by the decomposition of urea.
3
On heating a 1:12 mixture of NiMoO with urea we obtained a mixture of Ni Mo N and Ni. The XRD pattern of the
2
4
3
˚
product shown Fig. 1(c) confirms the formation of cubic Ni Mo N (a = 6.9001 A) and reveals the presence of nickel
impurity as required by the reaction (2).
2
3
3
NiMoO þ 8NH ! Ni Mo N þ Ni þ 12H O þ 7=2N
(2)
4
3
2
3
2
2
The structure of Ni Mo N is similar to that of Al Mo C with a filled b-Mn structure. The SEM image shown
2
2
3
3
Fig. 2(c) shows sub-micrometer sized particles. The presence of nickel was ascertained by magnetic measurements
which showed ferromagnetism.

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A. Gomathi / Materials Research Bulletin 42 (2007) 870–874
4
. Conclusions
In conclusion, we have been able to prepare three ternary nitrides of type M Mo N (n = 3 with M = Fe and Co and
n
3
n = 2 with M = Ni) by a simple reaction of the precursor molybdates with urea.
Acknowledgment
The author thanks Professor C.N.R. Rao for suggesting the problem and guidance.
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