AbstractMn-silicides have been synthesized by reaction between Si powder and MnCl2 vapour. The growth temperature varied from 400 °C to 500 °C. The resultant silicides powders were characterized by X-ray diffraction (XRD). By powder reaction, the silicidation temperature can be decreased to 400 °C. The dominant growth of HMS was obtained at the heating temperature of 500 °C for 36 h. The phase evolution was discussed and compared with bulk reaction. The electrical properties of Mn silicides tablets were measured

Guan, Shaokang

Hu, Junhua

Li, Wen

Tatsuoka, Hirokazu

Zhang, Caili

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Preparation and electrical properties of Mn silicides by reaction of MnCl2 and Si powder 

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Physics Procedia 00 (2010) 000–000 
www.elsevier.com/locate/procedia
Proceedings of APAC-SILICIDE 2010
Preparation and electrical properties of Mn silicides by reaction of MnCl2 and 
Si powder 
Junhua Hu1*, Caili Zhang2, Wen Li1,3, Shaokang Guan1, Hirokazu Tatsuoka3
1 School of Materials Science and Engineering, Zhengzhou University, Zhengzhou, 450002, PR China 
2School of Civil and Architecture Engineering, Zhongyuan Institute of Technology, Zhengzhou,450007, P.R.China 
3Shizuoka University, Hamamatsu, 432-8561, Japan 
Abstract 
Mn-silicides have been synthesized by reaction between Si powder and MnCl2 vapour. The growth temperature 
varied from 400 oC to 500 oC. The resultant silicides powders were characterized by X-ray diffraction (XRD). By 
powder reactionˈthe silicidation temperature can be decreased to 400oC. The dominant growth of HMS was 
obtained at the heating temperature of 500oC for 36h. The phase evolution was discussed and compared with bulk 
reaction. The electrical properties of Mn silicides tablets were measured. 
© 2009 Published by Elsevier B.V. 
Keyward: MnSi~1.7; X-Ray diffraction (XRD); MnSi; Silicides; electrical properties 
1. Introduction 
Semiconducting silicides have attracted much interest for their potential uses as environmentally friendly 
semiconductors [1]. Higher manganese silicides (HMS) with a composition near MnSi~1.7 are some of the 
semiconducting silicides with a direct band gap of about 0.7 eV, which are stable at high temperature, and are 
considered to be appropriate semiconducting materials for use in infrared photovoltaic devices, such as thermo-
photovoltaic batteries [2]. MnSi~1.7 has a tetragonal crystalline structure with a lattice constant of a = 0.553 nm and 
an unusually long c-axis up to 10 nm. The unusual crystalline structure of MnSi~1.7 makes it difficult to grow high 
quality films on highly symmetric Si substrates. At the same time, Mn-Si system indicates existence of several Si-
Mn intermediate phases. Multi-phase reaction always degrades the quality of HMS films and bulk materials [3~7].  
Several studies on the growth of HMS have been performed by solid phase epiatxy (SPE), reactive deposition 
epitaxy (RDE), ion beam epitaxy and molecular beam epitaxy (MBE) [4-7]. To improve the HMS continuity and 
* Corresponding author. Tel.: +86-371-63887505; fax: +86-371-63887508. 
E-mail address: hujh@zzu.edu.cn 
c⃝ 2010 Published by Elsevier B.V.
Physics Procedia 11 (2011) 138–141
www.elsevier.com/locate/procedia
1875-3892 c⃝ 2010 Published by Elsevier B.V.
doi:10.1016/j.phpro.2011.01.023
Open access under CC BY-NC-ND license.
Open access under CC BY-NC-ND license.
 J.Hu/ Physics Procedia 00 (2010) 000–000 
completeness, surfactant growth techniques based on the methods mentioned above have been used. In the case of 
HMS films grown in the presence of a surfactant (Sb) flux, it is impossible to control thermoelectric properties due 
to the presence of the surfactant atoms in the films as impurity. Even literature data [8] showed that impurity of Sb 
doped into manganese silicide bulk material led to decreasing of thermoelectric performance. In our previous work 
[9], manganese silicide layers were grown on Si (111) substrates by exposure of the Si substrates to MnCl2 vapour. 
At temperature of 400ć , not any Mn or silicides were deposited on the substrate. The thermal treatment 
temperature of 500 °C provided the appropriate growth conditions to form the MnSi~1.7 phase. The epitaxial MnSi~1.7
islands grew during the initial growth stage. As the heat treatment time increased, the epitaxial layer became 
continuous and covered the entire Si (111) substrate surface. However, the prepared films were too thin for practical 
applications. In present work, MnSi~1.7 was grown by using Si powder and MnCl2 as source materials. 
2. Experiment 
Mn-silicides powders were synthesized by exposure Si powder to MnCl2 vapour. MnCl2 was of analytical purity 
and was heated at 200 oC for 4h in vacuum to dehydrate it. An appropriate amount of Si powder and excess MnCl2
were mixed before being put into a loosely sealed glass container. Then the container was loaded into a vacuum 
chamber which was pumped down to the base pressure of 10-3 Pa. The container was heated and the growth 
temperature varied from 400 oC to 500 oC. During the heating process, Si powders were exposed to MnCl2 vapour. 
The phase composition of the resultant powders was characterized using X-ray diffraction (XRD). For the electrical 
measurement, the MnSi~1.7 powder were pressed at 10 MPa at room temperature to get tablets with a size of 1.5mm 
height and 5mm diameter.  
3. Results and discussion  
Fig.1 (a) shows the XRD spectra of Mn-silicides powder synthesized at the temperature of 400 oC for 2 hours. 
The formation of MnSi~1.7 as dominant silicides phase was observed. At the growth temperature of 500oC for 2h 
(Fig.1b), the same resultant phase was obtained. However, at 400 oC, the prolongation of growth time to 6h resulted 
in the enhanced growth of MnSi (Fig.2c). In Fig.2 (a) and (b), at 500 oC4h and 6h’s growth did not result in the 
evident growth of MnSi.  
Fig.1 XRD spectra of Mn-silicides prepared at400 o& and 500o&for 2 hours, respectively. 
J. Hu et al. / Physics Procedia 11 (2011) 138–141 139
 J.Hu/ Physics Procedia 00 (2010) 000–000  
In the reference [9], no deposition was observed on the Si substrates treated at 400 °C in MnCl2 vapour. The 
dissociation of MnCl2 and reaction of Si and Mn have been discussed in Ref.[9].Considering the fact that the 
treatment temperature of 400 °C is too low for dissociation of MnCl2 and reaction with bulk substrate, it can be 
concluded that surficial atoms on the Si powder are more active then atoms on bulk sample. The reaction of MnCl2
and surfacial Si atoms was responsible for the low temperature silicidation. At the same time, the solubility of Mn 
atoms in silicon is very low at this temperature (3 × 1012 /cm–3) [10]. It can be assumed if the mixing occurred it 
must depend on the bonds breaking and new bond formation. As MnSi~ 1.7 was formed, the Mn diffusion across the 
silicides layer was depressed since the metal was always thought inactive in the Si-rich silicides layer. Thus the 
MnSi phase was formed on the MnSi~1.7 layer. Roughly speaking, the Mn-rich silicides have a lower enthalpy of 
formation [11], and the Si-rich phases are more stable. Theoretical predication showed the first nucleation phase was 
Mn5Si3 [12]. It has also been shown that the silicides growth strongly depends on the interface conditions and not 
simply on the free energy of formation. The further structural characterization of resultant silicides powder will be 
required to clarify the phase selection and formation mechanism of Mn-silicides by powder reaction.  
Fig.2 XRD spectra of Mn-silicides prepared at different conditions 
In the Ca-Si and Sr-Si system, different phases formation was also found [13] by powder reaction. Heating the 
Si substrate in Ca or Sr vapour resulted in the formation of several silicide phases. However, by using Si powder, the 
single phase M5Si3(M=Ca,Sr) was grown. These results will help us to clarify the interface condition dependence of 
silicides growth. 
Based on the XRD characterization, the prolongation of growth time helped the formation of HMS at 500oC.
Fig.2 (d) shows XRD spectrum of Mn-silicide powder after treatment for 36h at 500oC, in which the diffraction 
peaks was assigned as MnSi~1.7 phase. Small amount of raw silicon powder can also be found. The tablets were 
made from the MnSi~1.7 powders for electrical properties measurement. The electrical conductivity of tablet varied 
from 25 to 30 (1/kȍǜm) at the temperature range of 300K -380K. Electrical conductivity and Seebeck coefficient of 
the tablet were shown in Fig.3. The power factor was calculated by Į2ı [14]. The power factor was increased from 
1.12h10-9 W/m-K2 (at room temperature ) to 1.21h10-9 W/m-K2 (at 373K).    
4. Conclusions 
140 J. Hu et al. / Physics Procedia 11 (2011) 138–141
 J.Hu/ Physics Procedia 00 (2010) 000–000 
Mn-silicides have been synthesized by reaction between Si powder and MnCl2 vapour. By powder reactionˈ
the formation temperature can be decreased to 400oC. The dominant growth of HMS was obtained at the heating 
temperature of 500oC for 36h. The phase evolution was discussed and compared with bulk reaction [9]. The 
electrical conductivity and powder factor at the temperature range of 300 - 400K were measured. 
Fig.3 Electrical conductivity and Seebeck coefficient of the silicides tablet. 
Acknowledgement 
This study was supported by National Natural Science Foundation of China (Grant No.51001091). We would 
like to express sincere thanks to Dr. Xiu for his help in the electrical properties experiment. 
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Preparation and electrical properties of Mn silicides by reaction of MnCl2 and Si powder

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