Crystallization behaviors of nanosized MgO particles from magnesium alkoxides
Introduction
MgO has received a great deal of attention for its applications in the chemical and electronic industries. MgO powder has been utilized as a catalyst [1], [2], [3], [4], [5], [6], [7], [8] and MgO thin films have been used as buffer layers for superconducting and ferroelectric thin films [9], [10], [11], [12], [13], [14], [15]. Furthermore, MgO thin films have been investigated for use as a protective layer in AC-plasma display panels (AC-PDP) [16], [17], [18], [19], [20]. The substrate used in these panels is made of a soda-lime silicate with a low melting temperature; one of the major requirements of the MgO thin film is a low crystallization temperature. Since the sol–gel process has the advantages of low crystallization temperature and low cost, sol–gel-derived MgO thin films have been studied intensively in recent years [12], [13], [14], [15].
To enhance the crystallization behavior of sol–gel-derived films or powders, the hydrolysis reaction of the component alkoxide was investigated as a function of the alkoxy radical size [21], amount of water [22], and acid and base catalysts [7], [22]. In our preliminary study, however, the MgO film deposited from a hydrolyzed sol was found to be unsuitable for the protective layer application in AC-PDP [23]. The film produced through the hydrolysis reaction demonstrated unstable secondary electron emission properties because of nanopores present in the film. The nanopores were formed during the topotactic reaction of Mg(OH)2 to MgO. This suggested that a new manufacturing approach was needed to prepare MgO film for application as protective layers. In that study, MgO films were prepared using a pyrolysis process, without an associated hydrolysis reaction. In the pyrolysis process, the selection of raw alkoxide is critical to the subsequent decomposition and the crystallization process of the films. Desu found that the deposition rate from a TEOS (tetraethoxysilane) source was higher than that from a TMOS (tetramethoxysilane) source in the CVD process [24]. The difference in the decomposition behavior was attributed to the size of the alkyl group. In the MgO system, the effect of the size of the alkoxy group was also studied. Thoms et al. investigated the decomposition mechanism of Mg–alkoxide and showed that MgO powder morphology depended on the Mg–alkoxy group size [25]. Considering that the decomposition of the alkoxy group is closely related to crystallization behavior, the difference in the size of the alkoxy group is expected to change the crystallization of the alkoxide. However, the decomposition and crystallization behavior of MgO has not been studied systematically as a function of the alkoxy group.
In this study, MgO powders were prepared from two types of Mg–alkoxides (magnesium methoxide and magnesium ethoxide). The thermal decomposition/crystallization behavior of the MgO was investigated from the viewpoint of the alkoxy group size to find the effect of the alkoxy group size.
Section snippets
Experimental
In the present study, magnesium ethoxide [Mg(OC2H5)2] in powder form (designated as ME) and a magnesium methoxide [Mg(OCH3)2] solution in methanol were selected. To prepare the magnesium methoxide powder (designated as MM) without the undesired hydrolysis reaction, the magnesium methoxide solution in methanol was dried in a vacuum chamber. The ME and MM powders were heat-treated under different thermal conditions; i.e., atmosphere and temperature. Heat-treated alkoxide powders were quenched at
Results
The FT-IR spectra of MM and ME raw precursors and powders quenched at 300, 350, 400, and 600 °C in N2 are shown in Fig. 1. The absorption bands in Fig. 1 were indexed according to Table 1, which summarizes the organic modes reported in the literature [13], [25], [29], [30], [31], [32]. The CO stretching mode observed at 1015–1130 cm−1 and the CH stretching mode observed at 2750–2970 cm−1 correspond to the alkoxy group. The absorption band (MgO stretching mode at 500–600 cm−1) in raw powders
Discussion
Using FT-IR and TGA data, we observed that the ME powder started decomposition at a lower temperature than the MM powder. These results revealed that the decomposition behavior of the alkoxide was influenced by the size of the alkoxy group. The alkoxide with a larger alkyl group began decomposition at a lower temperature. The difference in the decomposition temperature, in turn, influenced the crystallization of the resultant alkoxide powders. The XRD and TEM results revealed that the MgO from
Conclusions
(1) XRD and TEM results revealed a different in crystallization behavior in MgO powders. The magnesium oxide phase was not observed in the methoxide powder, but in the magnesium ethoxide one, processed at the same temperature. This suggests that the crystallization behavior of MgO powders is influenced by the type of alkoxide used in processing.
(2) TG analysis in N2 showed that the initial decomposition temperature of the alkoxide was approximately 330 °C for magnesium methoxide and
Acknowledgements
This work was funded by the Center for Iron & Steel Research. The authors would also like to thank Ki Ho Maeng for kindly supporting TEM measurement.
References (35)
- et al.
Mater. Sci. Eng. B
(1999) - et al.
Solid State Ionics
(1997) - et al.
Chem. Mater.
(1991) - et al.
Chem. Mater.
(1996) - et al.
Chem. Mater.
(1993) - et al.
Chem. Mater.
(1998) - et al.
Kinet. Catal.
(1997) - et al.
Langmuir
(1996) - et al.
Solid State Chem.
(1995) - et al.
Chem. Mater.
(1996)
Appl. Phys. Lett.
J. Cryst. Growth
Appl. Phys. Lett.
J. Mater. Res.
Chem. Mater.
Appl. Phys. Lett.
J. Sol–Gel Sci. Technol.
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Current address: Los Alamos National Laboratory, Los Alamos, NM 87545, USA.