Novel electrochemical technique: Grain control in preparation of polycrystalline BaMoO4 film

Article abstract of DOI:10.1016/j.materresbull.2007.06.001

BaMoO₄ films have been prepared by a novel electrochemical technique without impressed current on molybdenum substrates at room temperature in barium hydroxide aqueous solution. In order to form desired surface morphology and grain size, the BaMoO₄ crystal grains have been controlled effectively by adjusting ion-concentration and adding adequate surfactant. The as-prepared BaMoO₄ films have been characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM and XRD results indicate that the morphology, grain size, phase and crystallinity were significantly developed.

Full text of DOI:10.1016/j.materresbull.2007.06.001

Materials Research Bulletin 43 (2008) 1160–1163
www.elsevier.com/locate/matresbu
Novel electrochemical technique: Grain control in preparation of
polycrystalline BaMoO film
4
*
Chunhua Cui, Jian Bi , Chunyan Wu, Shu Zhang, Daojiang Gao
College of Chemistry and Materials Science, Sichuan Normal University, Chengdu 610066, PR China
Received 23 January 2007; accepted 3 June 2007
Available online 7 June 2007
Abstract
BaMoO
4
films have been prepared by a novel electrochemical technique without impressed current on molybdenum substrates at
room temperature in barium hydroxide aqueous solution. In order to form desired surface morphology and grain size, the BaMoO4
crystal grains have been controlled effectively by adjusting ion-concentration and adding adequate surfactant. The as-prepared
BaMoO
XRD results indicate that the morphology, grain size, phase and crystallinity were significantly developed.
2007 Elsevier Ltd. All rights reserved.
4
films have been characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM and
#
Keywords: A. Thin films; B. Chemical synthesis; B. Crystal growth; C. X-ray diffraction
1
. Introduction
Molybdates such as CaMoO , SrMoO and BaMoO with a scheelite structure is an important luminescent material
4
4
4
that has a high application potential due to it showed scintillating luminescent character [1–3]. In recent years, various
architectures such as nanostructures BaMoO (spindle arrays, bundle-like and brush-like), powders and nanofibers
4
have been extensively investigated [3–7]. Currently, the preparation of ceramic films is attracting much great interest
for a wide variety of applications in electronics, optics, ionics and anticorrosion coatings of metals and alloys [8].
However, the surface morphology and grain size have great direct impact on compact, lattice parameter and optical
performance of BaMoO film. Thus, a novel electrochemical method may favor the formation of high compact and
4
morphology
Recently, our research effort has been devoted to the improvement of surface morphology of BaMoO films by a
4
novel electrochemical technique. In this paper, we reported the partial optimized deposition conditions of this kind of
preparation technology, and the films fabricated by this method have uniform and homogeneous surfaces.
2
. Experimental
Molybdenum metal substrates with 99.5 wt.% in purity and dimensions of 15 mm  30 mm  0.2 mm were used
as reaction substrates. The counter electrodes (cathode) were nickel. After mechanical polishing and composite
*
Corresponding author. Tel.: +86 28 84760802; fax: +86 28 84767868.
E-mail addresses: cuichunhua119@163.com (C. Cui), bijian686@126.com (J. Bi).
0025-5408/$ – see front matter # 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2007.06.001

C. Cui et al. / Materials Research Bulletin 43 (2008) 1160–1163
1161
4
Fig. 1. (a) Schematic illustration of experimental setup and (b) flow chart of the preparation of BaMoO thin films.
strong-acid treatment, the molybdenum substrates were cleaned with an ultrasonic cleaner in deionized water solution
and finally dried. Polytetrafluoroethylene (PTFE) containers were used as the reaction vessels. A group of samples
have been obtained by different treatment concentrations with Ba(OH) solutions which were divided into saturation
2
concentration (0.0400 mol/L), 0.0200, 0.0133 and 0.0067 mol/L and the other group samples obtained by adding
cetyltrimethylammonium bromide (C H BrN) of 10 mg/L in 100 mL saturation Ba(OH) solution. The treatment
solutions were purged with N gas for 20 min to remove dissolved CO in PTFE containers, respectively. At last the
1
9
42
2
2
2
whole setup sealed totally is shown in Fig. 1(a). All the experiments were performed at room temperature for 160 h.
The samples were immersed in tepid deionized water solution for 5 min, and then dried at room temperature.
The grain size, morphology and microstructure were observed by SEM (SEM, JSM-5900, JEOL, Japan). The
resultant phase of the as-grown films was analyzed by XRD (XRD, Y-4Q SYSTEM Version 3.0, Dandong, China). The
X-ray diffraction studies were carried out in the range of scanning angle 20–808 using X-ray diffractometer with Cu
˚
Ka radiation of wavelength 1.54056 A at 36 kV and 30 mA.
3
. Results and discussion
The scanning electron micrographs in Fig. 2 show that the BaMoO films have been prepared by a novel
4
electrochemical method on molybdenum substrates in different treatment processes have different surface
morphology and grain size. As shown in Fig. 2(A), the crystal formed with a tetragonal structure grow preferentially in
the horizontal direction of the substrate, and the grain size is about 50–100 mm. These oversize crystals which hold
over many spaces and put apart a large number of interspaces at the junction of BaMoO crystal grains can result in low
4
uniformity and compact. At the same time the crystals grow preferentially along with the symmetric axis of square
bipyramid which is another factor to low compact. In order to control such preferential growth, both lowering the
concentration of Ba(OH) solutions and adding adequate surfactant seem to be the efficient methods. Fig. 2(B and C)
2
show the micrographs of BaMoO films with controlled crystal growth and desired compact surface morphology. It
4
can be seen that in Fig. 2(B) the grain size and preferential growth were controlled when the Ba(OH) concentration
2
decreased to 0.0067 mol/L. According to Pourbaix’s diagram [9] and Cho’s equation [8], metal Mo has a tendency to
2
dissolve and form MoO4 ions in alkaline solution in Fig. 1(b). Lower the concentration of Ba(OH) solutions may
À
2
2
restrain dominant growth, but dissolution–oxidation process requires higher pH to form MoO4 ions and high
À

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C. Cui et al. / Materials Research Bulletin 43 (2008) 1160–1163
Fig. 2. SEM images of as-prepared BaMoO
4
films prepared for 160 h: (A) obtained after being treated in saturation concentration (0.0400 mol/L),
(B) treated with the concentration of 0.0067 mol/L, and (C) treated in saturation concentration (0.0400 mol/L) by adding surfactant (C19H42BrN).
Fig. 3. XRD patterns as-prepared BaMoO
4
films prepared for 160 h: (a) obtained after being treated in saturation concentration (0.0400 mol/L), (b)
42BrN).
treated with the concentration of 0.0067 mol/L, and (c) treated in saturation concentration (0.0400 mol/L) by adding surfactant (C19
H
2
concentration of MoO4 and Ca ions favor the formation of BaMoO crystal nucleus, so the better processing
À
2+
4
concentration range is about 0.0133–0.0067 mol/L. In the present study, we have discovered room-temperature
synthesis of a well-crystallized luminescent BaMoO film that the adequate surfactant, C H BrN, may be another
resultful method to improve the crystallinity and compact. As shown in Fig. 2(C), the BaMoO film exhibits uniform
4
19 42
4
and homogeneous surfaces and the grain size decrease to about 10 mm. It shows that the grains are uniformity and
almost the whole surfaces of the substrate are covered with crystal BaMoO without any cracks and pores.
4
X-ray diffraction patterns of BaMoO films following different treatments are shown in Fig. 3(a–c), respectively.
4
Compared the XRD patterns of the samples to the JCPDS Files No. 72-0747, all the peaks of the films are identified to
belong to BaMoO , no extra peaks were detected. In Fig. 3(a), some characteristic weak peaks have not been observed;
4
it implies that the crystallinity and the compact of the BaMoO film are not very high. Both Fig. 3(b and c) show
4
excellent crystallinity and the films in this work were composed of only BaMoO phase. Several peaks appear at
4
2
reflections of the tetragonal structure of scheelite BaMoO film and some weak peaks are appearing such as (2 2 0),
u = 26.48, 27.78, 32.08, 42.98, 53.88 which can be, respectively attributed to (1 1 2), (0 0 4), (2 0 0), (2 0 4), (1 3 2)
4
(1 1 6), (2 0 8), (3 1 6). Especially in Fig. 3(c) the relative intensity of molybdenum substrate is quite low and that also
explains the desired surface morphology and crystallinity.
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. Conclusions
Highly crystallized BaMoO films have been successfully prepared by using novel electrochemical technique. A
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case study showing that morphology and grain size of prepared films can be simultaneously controlled by simple
tuning the preparation conditions and the whole progressing is inexpensive and environmentally friendly. The

C. Cui et al. / Materials Research Bulletin 43 (2008) 1160–1163
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as-improved BaMoO films have tetragonal structure with average grain size in 10 mm and have homogeneous and
4
uniform surfaces without any cracks. This novel electrochemical technique should be as a framework to design other
oxide films due to its advantages: (1) the reaction takes place in solutions, so additive can be easily added and even
more homogeneous, (2) this method without impressed current just depending on a counter electrode which eliminates
the need of a power supply, and micro-current may favor the transfer of cations in keeping certain dissolution rate. In
2
À
such micro-current density the cations embedded in the MoO4 easily, (3) dissolution–oxidation rate have been
abased, providing a more relaxed environment and the crystal growth is freer.
Acknowledgements
This work was supported by the NSFC (NO. 50472103), and the Major Project of Sichuan Education Bureau
2004A90). The authors would like to thank Wei Wang for valuable discussions.
(
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