Synthesis of Nanocrystalline Iron Monoarsenide via a Reductive Recombination Pathway

Article abstract of DOI:10.1006/jssc.1998.8103

Nanocrystalline FeAs was prepared with FeCl₃and AsCl₃as the reactants and Zn as reductant via a reductive recombination pathway in the temperature range of 150-180°C. The XRD pattern indicated the products were the single phase of iron monoarsenide. A TEM image showed the average size of the FeAs was about 20 nm. XPS gave the ratio of Fe to As 50.9:49.1. The influence of reactions and the possible reaction route of the formation of iron monoarsenide are discussed.

Full text of DOI:10.1006/jssc.1998.8103

Journal of Solid State Chemistry 144, 237}239 (1999)
Article ID jssc.1998.8103, available online at http://www.idealibrary.com on
Synthesis of Nanocrystalline Iron Monoarsenide
via a Reductive Recombination Pathway
X. M. Zhang, C. Wang, X. F. Qian, Y. Xie, and Y. T. Qianꢀ
Chemistry Department, University of Science and Technology of China, Hefei, Anhui 230026, People+s Republic of China
Received April 3, 1998, in revised form November 23, 1998, accepted November 24, 1998
In order to alleviate the time and energy cost, some new
Nanocrystalline FeAs was prepared with FeCl and AsCl as approaches have been introduced to prepare inorganic
3
3
the reactants and Zn as reductant via a reductive recombination
pathway in the temperature range of 150+1803C. The XRD
pattern indicated the products were the single phase of iron
monoarsenide. A TEM image showed the average size of the
FeAs was about 20 nm. XPS gave the ratio of Fe to As 50.9:49.1.
The in6uence of reactions and the possible reaction route of the
formation of iron monoarsenide are discussed. ( 1999 Academic Press
Key Words: iron monoarsenide; reductive recombination path-
way; nanocrystalline materials.
materials, such as the solvent}thermal synthesis (16}18). In
the process, starting materials can be solved in the solution
and therefore reaction can overcome the solid state di!usion
barrier, enabling the reactions to take place at a much lower
temperature. In this paper, the single phase of iron monoar-
senide was synthesized via a solvent}thermal reductive pro-
cess using Zn as the reductant in absolute ethanol in the
range of 150}1803C.
EXPERIMENT SECTION
INTRODUCTION
Because AsCl is toxic and susceptible to hydrolysis, all of
the manipulations were carried out in a dry-box, which was
ꢂ
Compound semiconductors, mainly metal pnictides, have "lled with nitrogen gas.
a wide variety of applications such as satellite TV receivers In a typical reaction, 0.01 mol anhydrous FeCl (99.5%,
1), optical "ber communications, (2) and compact dis- Shanghai Chemistry Co.) and 0.01 mol AsCl (Aldrich
ꢂ
(
ꢂ
players (3}4). Iron arsenides as technologically important as Chemistry Co., Ltd.) were put into a Te#on-lined autoclave
semiconductors (5}7), secondary high-temperature batte- with 100 ml capacity, and then 75 ml absolute ethanol
ries, (8) and catalysts (9) have attracted scientists' attention (99.5% purity, Shanghai Chemistry Co.) and 4.71 g Zn
for a long time. In addition to many other transition metal (99.5% purity, Shanghai Chemistry Co.) powder were ad-
arsenides, FeAs exhibits the orthorhomic B31 (MnP) struc- ded. The autoclave was sealed and maintained at 1503C for
ture with cell constant a"5.4361 A
s
, b"6.0242 A
s
, c" 12 h, then cooled to room temperature naturally. After
3
.3724 A, A"0.9023, C"0.5595 (10).
s
washing with absolute ethanol, 0.1 mol/L HCl solution, and
Conveniently, transition metal arsenides could be pre- distilled water, a black precipitate was collected. The "nal
pared by direct combination from the element metals and product was dried in a vacuum box at 803C for 4 h.
arsenic melted in an evacuated quartz tube and quenched at In order to understand the route of formation of FeAs,
003C (11). The thin "lm of a transition metal "lm could be FeCl and absolute ethanol were replaced by FeCl ) 4H O
9
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ꢁ
ꢁ
prepared from the metal-organic chemical vapor depos- (Shanghai Chemistry Co.) and benzene (Shanghai Chem-
itions of metal-organic precursors (12). Recently, Parkin et istry Co.), respectively (see Table 1).
al. synthesized a series of metal arsenides by solid state
metathesis (SSM) reactions with metal pnictides and metal corded on a Japan Rigaku cA X-ray di!ractometer using
halides as precursors at a typical temperature of 5003C; CuKa (j"1.54178 A), employing a scanning rate of
however, only a mixture of FeAs and Fe As was reported to 0.05 s\ꢀ in the 2h range from 103}703. A transmission elec-
The X-ray powder di!raction (XRD) pattern was re-
s
ꢁ
be obtained by this method (13}15).
tron microscope (TEM), with an accelerating voltage of
2
00 KV was used. The X-ray photoelectron spectrum (XPS)
was performed on a VGESCALAB MKII X-ray photo-
electron spectrometer, using nonmonchromatized MgKa
X-ray as the excitation source.
ꢀ
To whom correspondence should be addressed.
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37
0
022-4596/99 $30.00
Copyright ( 1999 by Academic Press
All rights of reproduction in any form reserved.

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38
ZHANG ET AL.
TABLE 1
Reaction Conditions for the Formation of FeAs
Reaction
Reagents
Other reagent
Solvent
Temp (3C)
Time (hr)
Product
1
2
3
FeCl #AsCl
Zn
Zn
Zn
ethanol
ethanol
benzene
150}180
160
160
12
12
12
FeAs
FeAs
no FeAs
ꢂ
ꢂ
FeCl )4H O#AsCl
ꢁ
ꢁ
ꢂ
FeCl #AsCl
ꢂ
ꢂ
RESULTS AND DISCUSSION
The process may be as follows:
The XRD pattern of the sample as-prepared in reaction
is shown in Fig. 1. All the peaks can be indexed as the
Zn#2CH CH OH 8 Zn(OCH CH ) #2H [1]
ꢂ ꢁ
ꢂ
ꢁ
ꢁ
1
orthorhombic FeAs phase which is consistent with the liter-
ature (JCPDS CARDS No. 12-799). The average crystalline
FeCl #AsCl #6H P FeAs#6HCl
[2]
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size determined by the Scherrer equation based on the XRD Zn(OCH CH ) #2HCl P ZnCl #2CH CH OH. [3]
ꢁ
ꢂ ꢁ
ꢁ
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half-width is in the range of 15 nm. The XPS pattern of the
sample also con"rms the formation of FeAs (see Fig. 2). Two So the overall reaction can be expressed as
strong peaks at 44.45 and 711.3 eV correspond to As3d
(
Fig. 2a) and Fe2p3 (Fig. 2b), respectively in the FeAs phase.
FeCl #AsCl #3Zn P FeAs#3ZnCl .
[4]
ꢂ
ꢂ
ꢁ
From the XPS pattern, the quali"cation of peaks gives the
ratio of Fe to As as 50.9:49.1 which is close to the chemical
composition of FeAs.
From the TEM micrograph (Fig. 3), we can see that the
FeAs particles consist of uniform spherical crystallites and
the average size is about 20 nm, which is consistent with
that from the XRD pattern.
The optimum conditions for synthesizing nanocrystalline
FeAs are in the range of 150}1803C for 12 h. As the temper-
ature is lower than 1403C or the time is less than 4 h, the
formation of FeAs is incomplete or even cannot be initiated.
However, with the temperature higher or the reaction time
longer, the size of the as-prepared particles would become
larger.
The actual route may be a reductive recombination path-
way in which the components are reduced to the elements.
FIG. 1. XRD pattern of FeAs prepared by the reaction of anhydrous
FIG. 2. XPS pattern of as-prepared FeAs products. (a) As3d peak of the
as-prepared FeAs. (b) Fe2p3 peak of the as-prepared FeAs.
FeCl and AsCl .
ꢂ
ꢂ

SYNTHESIS OF NANOCRYSTALLINE IRON MONOARSENIDE
239
CONCLUSION
In this paper, we successfully prepared a nanocrystalline
iron arsenide semiconductor through the reaction of FeCl
ꢂ
and AsCl via a reductive recombination process. The "nal
ꢂ
products were characterized by XRD, XPS, and TEM. We
also discussed the possible chemical formation process of
FeAs.
ACKNOWLEDGMENT
This work was supported by Climbing Program Research}National
Foundation Project and Chinese National Foundation of Natural Science
Research.
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problem. Because the tendency of alcohol to self-ionize is
signi"cantly less than that of water (PK (C H OH)!
1
(
!
ꢀꢁꢂ ꢁ ꢃ
PK (H O)"5.1) (21), the participation of the alcohol in
the solvolysis reaction is less pronounced, thought it can
with Zn at high temperature.
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of Zn powder should be in excess of 20%. The residue of Zn
powder can be removed by washing with dilute HCl (0.1 M)
solution.
!
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