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Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling
NOC-17384; No of Pages 5 Journal of Non-Crystalline Solids xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol
Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling Elena Petracovschi a, Bruno Bureau a, Alain Moreac b, Claire Roiland a, Jean-Luc Adam a, Xiang-Hua Zhang a, Laurent Calvez a,⁎ a b
UMR CNRS 6226 Institut des Sciences Chimiques de Rennes, Equipe Verres et Céramiques, Université de Rennes 1, 35042 Rennes Cedex, France UMR CNRS 6251 Institut de Physique de Rennes, Université de Rennes 1, 35042 Rennes Cedex, France
a r t i c l e
i n f o
Article history: Received 15 November 2014 Received in revised form 29 March 2015 Accepted 9 April 2015 Available online xxxx Keywords: Chalcogenide glasses; Mechanical milling; Raman spectroscopy; 77Se NMR
a b s t r a c t Amorphous powders of GeSe4 and 80GeSe2–20Ga2Se3 compositions have been prepared by mechanical alloying of raw Germanium, Selenium and Gallium. The amorphization process and structural evolution of the powder during mechanical alloying have been studied by XRD, DSC, Raman spectroscopy and 77Se NMR. The role of Gallium in the amorphization process has been pointed out. Similar structures and thermal properties of amorphous powders and respective glasses synthesized by melt-quenching method have been observed. © 2015 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental procedures
Chalcogenide glasses (ChG) are transparent in near and mid infrared (IR) ranges and have proven their effectiveness in different fields of applications as sensors, laser amplifier and especially as lenses for the night vision devices [1–4]. ChG are usually synthesized under vacuum in order to avoid their contamination by the molecules that vibrate in their range of transparency. Nevertheless, the use of ChG is still restricted by their low mechanical properties and especially their high final price which is due to the use of expensive purified elements and nonreusable silica tubes. We have recently demonstrated the feasibility to obtain bulk ChG by combining mechanical milling and sintering [5,6]. This new technology avoids the use of silica tubes, allows a glass synthesis at room temperature and leads to the production of new compositions and bigger size samples. Moreover, by adjusting sintering parameters, this process also permits the fast and simultaneous synthesis of glass-ceramics having higher mechanical characteristics than glasses. The first step of this process consists in making an amorphous powder by grinding raw metallic elements in a planetary grinder. This work was focused on the understanding of the amorphization process and of the structural evolution along the milling using XRD, DSC, Raman spectroscopy and solid state NMR analyses. Indeed, over the past 10 years, 77Se NMR was found to be a very good technique for probing the structure of ChG [7–11].
2.1. Glass powder synthesis
⁎ Corresponding author. E-mail address: [email protected] (L. Calvez).
Amorphous chalcogenide powder of GeSe4 and 80GeSe2–20Ga2Se3 compositions has been synthesized using the same conditions of mechanical alloying by introducing stoichiometric amounts of pure raw metallic Germanium (5 N, Umicore), Selenium (5 N, Umicore) and Gallium (5 N, Materion) in a tungsten carbide (WC) grinding jar containing 6 WC milling balls, with a ball-to-powder weight ratio 18.75:1. The jar was introduced into a planetary grinder (Retsch PM100, Germany). Rotation cycles of 3 min at 300 rpm were scheduled with direction reversal and a pause of 3 min between each cycle. The milling process has been periodically stopped and a small amount of the powder (~0.1 g) has been taken out for analysis. 2.2. Powder characterizations X-ray diffraction was carried out on the powder taken out after different milling durations using a Philips PW3710 diffractometer (Cu Kα1,2 1.5418 Å) in the range of 10–90° (2θ). Thermal properties of the powders were analyzed by Differential Scanning Calorimetry (DSC) using 10 mg of the sample and a ramp of 10 °C/min (DSC Q20; TA Instruments, New Castle, DE). A HR800 (Horiba/Jobin-Yvon) micro-raman spectrometer was used to collect unpolarized Raman spectra of all GeSe4 and 80GeSe2–20Ga2Se3 glassy powders in backscattering geometry at ambient temperature. These Raman measurements have been performed with a He–Ne laser at 633 nm for GeSe4 samples and with
http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015 0022-3093/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
2
E. Petracovschi et al. / Journal of Non-Crystalline Solids xxx (2015) xxx–xxx
a laser diode at 785 nm for 80GeSe2–20Ga2Se3 powders. Optical density filters were used to decrease the laser power to avoid heating at the focus point of the laser on the sample. The spectral dispersion was less than 1 cm− 1 per CCD pixel. The 77Se (S = 1/2) NMR spectra were recorded at room temperature on an Avance 300 Bruker spectrometer operating at 57.28 MHz with a 4 mm MAS probe spinning at 14 kHz. Full echoes were used to refocus the whole magnetization and avoid base line distortion. The time delay between the both pulses corresponds to one rotor rotation period. The recycle time was 300 s in agreement with recent results showing that long time is essential to get some quantitative spectra [12].
3.3. Differential scanning calorimetry The evolution of the transition temperature during the milling has already been discussed in several previous papers [5,6]. In this work the Tg values have been registered on the powder obtained at the end of the milling which have been identified as completely amorphous using XRD analysis. The two Tg are 168 °C for the GeSe4 composition and 370 °C for the 80GeSe2–20Ga2Se3 one, which are similar to the values registered for these two glasses obtained by the meltquenching method (165 °C for GeSe4 and 370 °C for 80GeSe2– 20Ga2Se3) [13–15]. 3.4. Raman spectroscopy
3. Results and discussions 3.1. Coloration of the powder The evolution of the color of GeSe4 and 80GeSe2–20Ga2Se3 (Ge23.53Ga11.76Se64.71) components is presented in Fig. 1. One can see that in the case of the ternary system the color changes from gray to brick-red after only 30 min of milling (Fig. 1b) which indicates a fast reaction between elements. On the contrary, in the case of the binary system, the change of the color occurs after around 30 or 50 h of milling (Fig. 1a). This latter result underlines that the interaction between Germanium and Selenium is slow during mechanical milling. Such a behavior of these two compounds observed in the same conditions of milling (ball-to-powder ration, rotation speed) indicates that Gallium plays an accelerator role in the amorphization process. Taken into account the very low melting point of Gallium (29.76 °C) and the transformation of the mechanical energy into a thermal one during milling, the melting of Gallium may be supposed, acting as a liquid medium which facilitates the diffusion of elements. The very fast amorphization of the ternary system could be explained by both a local melt-quenching of elements and their progressive diffusion during impacts.
3.2. X-ray diffraction XRD analyses have been performed on the powder extracted all along the milling process, as presented in Fig. 2. In both cases, GeSe4 and 80GeSe2–20Ga2Se3, diffraction pattern corresponding to Germanium has only been observed. Selenium and Gallium react relatively fast forming an amorphous powder. Completely amorphous powders have been obtained after 110 h of milling in the case of GeSe4 composition and after 50 h for 80GeSe2–20Ga2Se3. This result is in complete agreement with the evolution of the color of the two compounds, which has already pointed out the much faster interaction of Germanium and Selenium in the presence of Gallium.
a)
1h
10 h
b)
0h
30 min
30 h
5h
3.4.1. GeSe4 Raman spectroscopy has been used in order to study the structure of the completely amorphous powder. In Fig. 3, three bands can be identified at 195 cm− 1, 215 cm− l and 260 cm− 1. The band at 195 cm−1 corresponds to the A1 breathing mode of corner-sharing (CS) GeSe4/2 tetrahedral units and the band at 215 cm−1 is associated to the Ac1 breathing like motions (companion peak) of edge-sharing (ES) GeSe4/2 units [16–18]. The difference in the intensities of these bands indicates that the structure of the amorphous material is mainly based on CS tetrahedral units while ES units are presented in a small quantity. The third band at 260 cm−1 corresponds to the A1 and E2 modes of Se–Se bonds from chains or cycles constituted of Se atoms [16–19]. This peak indicates the presence of Selenium-rich phases in the final structure of GeSe4 glass. A comparison between this spectrum and the one corresponding to the same glass made by the melt-quenching method has also been done. The same bonds are observed on both spectra indicating that the same structure is reached in both materials synthesized using the two different methods. 3.4.2. 80GeSe2–20Ga2Se3 Spectra presented in Fig. 4 have been normalized according to the most intense band (200 cm−1). One can see that the interaction between the three elements occurs fast. Already after 1 h of milling, bands associated with GeSe4/2 units can be distinguished together with Se–Se and metal–metal interactions. With the increase of the milling time, the shape of spectra is not changing, only the intensity of bands is modified. Three areas can be identified on the Raman spectra: 75–150 cm−1, 150–230 cm−1 and 230–350 cm−1. In the first domain several distortional vibrations of Ge–Se or Se–Se bonds give such a broad band as in the case of GeSe4 composition [20,21]. In the second area an intense band centered at 200 cm−1 with two shoulders at 178 and 215 cm−1 can be distinguished. The peak at 200 cm−1 is associated with the A1 symmetric mode of CS GeSe4/2 units [20,21]. Two shoulders correspond respectively to the stretching of Ge– Ge bond in the ethane-like units (Se3/2)Ge–Ge(Se3/2) (178 cm−1) and
50 h
10 h
20 h
70 h
30 h
90 h
40 h
110 h
50 h
Fig. 1. Evolution of the color of the a) GeSe4 and b) 80GeSe2–20Ga2Se3 powder with the milling duration.
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
E. Petracovschi et al. / Journal of Non-Crystalline Solids xxx (2015) xxx–xxx
a)
3
b) 110 h 90 h 70 h 50 h 30 h 10 h 1h Ge
50 h 40 h 30 h 20 h 10 h Ge
Fig. 2. XRD patterns of the a) GeSe4 and b) 80GeSe2–20Ga2Se3 powders obtained after different milling durations.
to the symmetric in phase stretching of ES tetrahedral units (215 cm−1) [20–22]. Between 230 and 350 cm−1, three bands of low intensity can be observed at 240, 260 and 300 cm−1. The band at 240 cm−1 has been assigned in previous articles to an out of phase stretching of Se–Se bond in ES GeSe4/2 tetrahedral units [20,22,23]. Two assignments can be proposed for the broad band centered at 260 cm−1. A strong band at 252 cm−1 observed in glassy Se has been assigned to the A1 stretching mode of Se8 ring molecules [20]. P. Nemec et al. have assigned a band at 268 cm−1 observed in Ge25Ga5Se70 and Ge30Ga5Se65 glasses to A1 modes of vibration of Se chains [20]. Low intensity peak registered at 300 cm−1 has been assigned to an asymmetric stretching of CS GeSe4/2 units [21]. According to Fig. 4, the intensity of the band associated with the Se– Se bond vibration (domain 250–290 cm−1) is decreasing while the milling time is increasing. This trend indicates that the quantity of Selenium interacting with metals is increasing. However, the broad signal around 250 cm−1 has not totally disappeared indicating that a Se-rich domain remains in the final structure of 80GeSe2–20Ga2Se3 glass.
3.5. 77Se NMR 3.5.1. GeSe4 77 Se solid state NMR has been used to analyze powder samples starting by the initial raw Selenium. As one can see in Fig. 5, the peak centered on 850 ppm and corresponding to Se–Se–Se interactions presents a relatively large FWHM. In this way commercial Selenium
GeSe4/2
used for the mechanical alloying appears to be clearly vitreous. At the beginning of milling, from 10 min to 30 h, a part of Selenium (δiso = 850 ppm) becomes crystalline and when the milling time increases, beyond 30 h, it goes back amorphous. Other crystalline phases formed in the very beginning of the milling are distinguished giving rise to sharp lines between 200 and 700 ppm. Those are different Gex–Sey crystalline phases containing Se–Se–Ge or Ge–Se–Ge signals. Even if a clear assignment is not easy due to the signal to noise ratio, these sets of sharp lines look like those of the crystalline β-GeSe2 [18]. These lines disappear for long milling time. Surprisingly, between 30 and 50 h of milling it is difficult to detect 77Se lines corresponding to Selenium bonded to Germanium. Then, during the last 60 h of milling, the peak corresponding to amorphous Selenium (Se–Se–Se) is decreasing while Se–Se–Ge/Ge– Se–Ge peak is increasing in a significant way, as shown in Fig. 6a. The milling process has been continued up to 185 h in order to observe the evolution of the Se–Se–Se lines and the way that Se atoms incorporate the Ge–Se network. After 110 h of milling a saturation threshold of Se bridging Ge is reached. This result is coherent with the Raman spectroscopic analysis and confirms previous observations of Se rich domains in GeSe4 glass, i.e. rings or longer Se chains [24–27]. Spectrum obtained for the completely amorphous powder was also compared with the curve obtained for glasses synthesized by conventional melt-quenching method at different temperatures (Fig. 6b). Both curves exhibit the same shape which attests that the same structure of the glassy systems is reached by two different techniques, melt-quenching and mechanical alloying. Furthermore, the peak corresponding to amorphous Se is rather lower in the case of GeSe4 synthesized by mechanical alloying. In that way mechanical alloying
Se-Se
GeSe4/2
Fig. 3. Raman spectra of GeSe4 glass synthesized by melt-quenching method and of the completely amorphous powder obtained by mechanical milling.
Fig. 4. Raman spectra of the powder obtained after 1, 3, 5, 7, 10, 20 and 50 h of milling (normalized regarding to the peak at 200 cm−1).
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
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Se-Se-Ge Ge-Se-Ge
Se-Se-Se
110 h 70 h 30 h
50 h
1h
30 h
30 min
1h
10 min 0 min (raw Se)
30 min 1500
500
1000
10 min 0 min (raw Se) 1500
1000
500 iso
0
77Se
permits to incorporate more Se in the Ge–Se network, in a comparable manner to a quenching from a very high temperature. 3.5.2. 80GeSe2–20Ga2Se3 Fig. 7 presents 77Se NMR spectra registered from the raw initial Selenium and on the powder samples obtained after 10 min, 30 min, 1 h and 50 h of milling. As in the case of the binary system GeSe4, Selenium peak (Se–Se–Se, δiso = 850 ppm) becomes narrower after 10 min of milling showing a crystallization of the selenium. With increasing milling time, Selenium returns amorphous and the intensity of its peak is decreasing for the benefit of the second peak corresponding to the interactions between Selenium and the two metals (Se–Se–Ge, Ge–Se–Ge, Se–Se–Ga, Ga–Se–Ga, Ge–Se–Ga, δiso = 405 ppm) [23]. It is worthy to note that the second peak appears after only 30 min of milling confirming the rapid initiation of the interaction between all the elements. The comparison between spectra obtained for the completely amorphous powder and for a 80GeSe2–20Ga2Se3 glass synthesized by melt-quenching, confirms the obtainment of the same structure of samples (Fig. 8a). Indeed, the same shape of the spectra is observed. In addition, the deconvolution of the spectrum registered on the completely amorphous powder has pointed out the presence of
a)
50 h 70 h 90 h 110 h 135 h 185 h
1000 iso
500 77Se
77Se
0
(ppm)
-500
-1000
Fig. 7. 77Se NMR spectra of raw initial Selenium and of 80GeSe2–20Ga2Se3 powder samples obtained after 10 min, 30 min, 1 h and 50 h of milling.
-500
(ppm)
Fig. 5. 77Se solid state NMR spectra of initial raw Selenium and of GeSe4 powder samples obtained at different milling durations.
1500
iso
0
(ppm)
-500
amorphous Selenium which does not react with the other elements (Fig. 8b). Even if the respective contribution is low (4%), this result has also been observed using Raman spectroscopy and indicates the presence of Selenium-richer domains. These latter domains have also been observed in Selenium-rich glasses such as GeSe4 where the Se–Se–Se contribution is around 30–40% [24–27]. It is nevertheless quite surprising to detect amorphous Selenium in the glass composition 80GeSe2– 20Ga2Se3 (Ge23.53Ga11.76Se64.71) where the Se rate is much lower. 4. Conclusion Glassy powders of GeSe4 and 80GeSe2–20Ga2Se3 compositions have been obtained by mechanical alloying of metallic raw Germanium, Selenium and Gallium. The same thermal (Tg) and spectroscopic (Raman spectroscopy, 77Se NMR) characteristics have been observed for the completely amorphous powders that for the respective glasses synthesized by the melt-quenching method. Using the same conditions of alloying (speed rotation, ball-topowder ratio) the necessary milling time to obtain a completely amorphous powder has been shortened by a factor of 2 by adding Gallium to the Ge–Se system. The low melting point of Gallium (29.76 °C) is reached in the milling jar during alloying and the acceleration of the interaction between Ge and Se elements in the presence of Ga may be due to a localized and very fast melt-quenching phenomenon combined to a diffusion process of elements. For GeSe4, the crystallization of Selenium and of several Gex–Sey phases (very probably GeSe2) has been observed under the mechanical alloying. A much longer milling time was conducted to the amorphization
b)
Melt-quenching from 880°C Melt-quenching from 1100°C 110 h of milling
1500 1000 500 iso
77Se
0
-500
(ppm)
Fig. 6. 77Se solid state NMR spectra of a) GeSe4 powder samples obtained after 50, 70, 90, 110, 135 and 185 h of milling and b) GeSe4 powder (110 h of milling) and GeSe4 glasses synthesized by melt-quenching method.
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
E. Petracovschi et al. / Journal of Non-Crystalline Solids xxx (2015) xxx–xxx
a)
50 h of milling Melt-quenching
b)
5
50 h ofmilling
Se-Se-Se
1800
1200
600 iso
77Se
0
-600
-1200
(ppm)
2000
1000 iso
77Se
0
-1000
(ppm)
Fig. 8. a) 77Se NMR spectra of the completely amorphous powder (50 h of milling) and of the 80GeSe2–20Ga2Se3 glass synthetized by melt-quenching method. b) Deconvolution of 77Se NMR spectrum of the 80GeSe2–20Ga2Se3 powder obtained after 50 h of milling.
of these phases, confirming that this famous glass composition is not easy to get from a thermodynamic point of view, and that the final material does not exhibit a homogenous structural network. Acknowledgment This work has been supported by Umicore IR Glass and Region Bretagne. References [1] A. Zakery, S.R. Elliott, J. Non-Cryst. Solids 330 (2003) 1–12. [2] X.-H. Zhang, Y. Guimond, Y. Bellec, J. Non-Cryst. Solids 326–327 (2003) 519–523. [3] B. Bureau, C. Boussard-Plédel, P. Lucas, X.-H. Zhang, J. Lucas, Molecules 14 (2009) 4337–4350. [4] X.-H. Zhang, B. Bureau, C. Boussard-Plédel, H.-L. Ma, J. Lucas, Chemistry (Easton) 14 (2008) 432–442. [5] M. Hubert, G. Delaizir, J. Monnier, C. Godart, H.-L. Ma, X.-H. Zhang, L. Calvez, Opt. Express 19 (2011) 23513–23522. [6] E. Petracovschi, M. Hubert, J.-L. Adam, X.-H. Zhang, L. Calvez, Phys. Status Solidi B (2013) 1–4. [7] B. Bureau, C. Boussard-Plédel, M. Le Floch, J. Troles, F. Smektala, J. Lucas, J. Phys. Chem. B 109 (2005) 6130–6135. [8] G. Yang, B. Bureau, T. Rouxel, Y. Gueguen, O. Gulbiten, C. Roiland, E. Soignard, J.L. Yarger, J. Troles, J.-C. Sangleboeuf, P. Lucas, Phys. Rev. B 82 (2010) 195206–195214. [9] M. Deschamps, C. Roiland, B. Bureau, G. Yang, L. Le Polles, D. Massiot, Solid State Nucl. Magn. Reson. 40 (2011) 72–77.
[10] K. Sykina, G. Yang, C. Roiland, L. Le Polles, E. Le Fur, C.J. Pickard, B. Bureau, E. Furet, Phys. Chem. Chem. Phys. 15 (2013) 6284–6292. [11] D.C. Kaseman, I. Hung, Z. Gan, B. Aitken, S. Currie, S. Sen, J. Phys. Chem. B 118 (2014) 2284–2293. [12] K. Sykina, B. Bureau, L. Le Polles, C. Roiland, M. Deschamps, C.J. Pickard, E. Furet, Phys. Chem. Chem. Phys. 16 (2014) 17975–17982. [13] Y.-F. Niu, J.-P. Guin, T. Rouxel, A. Abdelouas, J. Troles, F. Smektala, J. Am. Ceram. Soc. 92 (2009) 1779–1787. [14] J. Troles, V. Shiryaev, M. Churbanov, P. Houizot, L. Brilland, F. Desevedavy, F. Charpentier, T. Pain, G. Snopatin, J.L. Adam, Opt. Mater. (Amst) 32 (2009) 212–215. [15] M. Rozé, L. Calvez, Y. Ledemi, M. Allix, G. Matzen, X.-H. Zhang, J. Am. Ceram. Soc. 91 (2008) 3566–3570. [16] K.D. Machado, J.C. de Lima, C.E.M. Campos, A.A.M. Gasperini, S.M. de Souza, C.E. Maurmann, T.A. Grandi, P.S. Pizani, Solid State Commun. 133 (2005) 411–416. [17] S. Sugai, Phys. Rev. B 35 (1987) 1345–1361. [18] E.L. Gjersing, S. Sen, J. Phys. Chem. C 114 (2010) 8601–8608. [19] S. Kohara, A. Goldbach, N. Koura, M.-L. Saboungi, L.A. Curtiss, Chem. Phys. Lett. 287 (1998) 282–288. [20] P. Nemec, B. Frumarova, M. Frumar, J. Non-Cryst. Solids 270 (2000) 137–146. [21] A.W. Mao, B.G. Aitken, R.E. Youngman, D.C. Kaseman, S. Sen, J. Phys. Chem. B 117 (2013) 16594–16601. [22] R. Holomb, V. Mitsa, E. Akalin, S. Akyuz, M. Sichka, J. Non-Cryst. Solids 373–374 (2013) 51–56. [23] D.C. Kaseman, I. Hung, Z. Gan, S. Sen, J. Phys. Chem. B 117 (3) (2013) 949–954. [24] D.C. Kaseman, I. Hung, Z. Gan, S. Sen, J. Phys. Chem. B 117 (2013) 949–954. [25] K. Sykina, E. Furet, B. Bureau, S. Le Roux, C. Massobrio, Chem. Phys. Lett. 547 (2012) 30–34. [26] T.G. Edwards, S. Sen, E.L. Gjersing, J. Non-Cryst. Solids 358 (2012) 609–614. [27] B. Bureau, J. Troles, M. Le Floch, P. Guénot, F. Smektala, J. Lucas, J. Non-Cryst. Solids 319 (2003) 145–153.
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol
Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling Elena Petracovschi a, Bruno Bureau a, Alain Moreac b, Claire Roiland a, Jean-Luc Adam a, Xiang-Hua Zhang a, Laurent Calvez a,⁎ a b
UMR CNRS 6226 Institut des Sciences Chimiques de Rennes, Equipe Verres et Céramiques, Université de Rennes 1, 35042 Rennes Cedex, France UMR CNRS 6251 Institut de Physique de Rennes, Université de Rennes 1, 35042 Rennes Cedex, France
a r t i c l e
i n f o
Article history: Received 15 November 2014 Received in revised form 29 March 2015 Accepted 9 April 2015 Available online xxxx Keywords: Chalcogenide glasses; Mechanical milling; Raman spectroscopy; 77Se NMR
a b s t r a c t Amorphous powders of GeSe4 and 80GeSe2–20Ga2Se3 compositions have been prepared by mechanical alloying of raw Germanium, Selenium and Gallium. The amorphization process and structural evolution of the powder during mechanical alloying have been studied by XRD, DSC, Raman spectroscopy and 77Se NMR. The role of Gallium in the amorphization process has been pointed out. Similar structures and thermal properties of amorphous powders and respective glasses synthesized by melt-quenching method have been observed. © 2015 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental procedures
Chalcogenide glasses (ChG) are transparent in near and mid infrared (IR) ranges and have proven their effectiveness in different fields of applications as sensors, laser amplifier and especially as lenses for the night vision devices [1–4]. ChG are usually synthesized under vacuum in order to avoid their contamination by the molecules that vibrate in their range of transparency. Nevertheless, the use of ChG is still restricted by their low mechanical properties and especially their high final price which is due to the use of expensive purified elements and nonreusable silica tubes. We have recently demonstrated the feasibility to obtain bulk ChG by combining mechanical milling and sintering [5,6]. This new technology avoids the use of silica tubes, allows a glass synthesis at room temperature and leads to the production of new compositions and bigger size samples. Moreover, by adjusting sintering parameters, this process also permits the fast and simultaneous synthesis of glass-ceramics having higher mechanical characteristics than glasses. The first step of this process consists in making an amorphous powder by grinding raw metallic elements in a planetary grinder. This work was focused on the understanding of the amorphization process and of the structural evolution along the milling using XRD, DSC, Raman spectroscopy and solid state NMR analyses. Indeed, over the past 10 years, 77Se NMR was found to be a very good technique for probing the structure of ChG [7–11].
2.1. Glass powder synthesis
⁎ Corresponding author. E-mail address: [email protected] (L. Calvez).
Amorphous chalcogenide powder of GeSe4 and 80GeSe2–20Ga2Se3 compositions has been synthesized using the same conditions of mechanical alloying by introducing stoichiometric amounts of pure raw metallic Germanium (5 N, Umicore), Selenium (5 N, Umicore) and Gallium (5 N, Materion) in a tungsten carbide (WC) grinding jar containing 6 WC milling balls, with a ball-to-powder weight ratio 18.75:1. The jar was introduced into a planetary grinder (Retsch PM100, Germany). Rotation cycles of 3 min at 300 rpm were scheduled with direction reversal and a pause of 3 min between each cycle. The milling process has been periodically stopped and a small amount of the powder (~0.1 g) has been taken out for analysis. 2.2. Powder characterizations X-ray diffraction was carried out on the powder taken out after different milling durations using a Philips PW3710 diffractometer (Cu Kα1,2 1.5418 Å) in the range of 10–90° (2θ). Thermal properties of the powders were analyzed by Differential Scanning Calorimetry (DSC) using 10 mg of the sample and a ramp of 10 °C/min (DSC Q20; TA Instruments, New Castle, DE). A HR800 (Horiba/Jobin-Yvon) micro-raman spectrometer was used to collect unpolarized Raman spectra of all GeSe4 and 80GeSe2–20Ga2Se3 glassy powders in backscattering geometry at ambient temperature. These Raman measurements have been performed with a He–Ne laser at 633 nm for GeSe4 samples and with
http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015 0022-3093/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
2
E. Petracovschi et al. / Journal of Non-Crystalline Solids xxx (2015) xxx–xxx
a laser diode at 785 nm for 80GeSe2–20Ga2Se3 powders. Optical density filters were used to decrease the laser power to avoid heating at the focus point of the laser on the sample. The spectral dispersion was less than 1 cm− 1 per CCD pixel. The 77Se (S = 1/2) NMR spectra were recorded at room temperature on an Avance 300 Bruker spectrometer operating at 57.28 MHz with a 4 mm MAS probe spinning at 14 kHz. Full echoes were used to refocus the whole magnetization and avoid base line distortion. The time delay between the both pulses corresponds to one rotor rotation period. The recycle time was 300 s in agreement with recent results showing that long time is essential to get some quantitative spectra [12].
3.3. Differential scanning calorimetry The evolution of the transition temperature during the milling has already been discussed in several previous papers [5,6]. In this work the Tg values have been registered on the powder obtained at the end of the milling which have been identified as completely amorphous using XRD analysis. The two Tg are 168 °C for the GeSe4 composition and 370 °C for the 80GeSe2–20Ga2Se3 one, which are similar to the values registered for these two glasses obtained by the meltquenching method (165 °C for GeSe4 and 370 °C for 80GeSe2– 20Ga2Se3) [13–15]. 3.4. Raman spectroscopy
3. Results and discussions 3.1. Coloration of the powder The evolution of the color of GeSe4 and 80GeSe2–20Ga2Se3 (Ge23.53Ga11.76Se64.71) components is presented in Fig. 1. One can see that in the case of the ternary system the color changes from gray to brick-red after only 30 min of milling (Fig. 1b) which indicates a fast reaction between elements. On the contrary, in the case of the binary system, the change of the color occurs after around 30 or 50 h of milling (Fig. 1a). This latter result underlines that the interaction between Germanium and Selenium is slow during mechanical milling. Such a behavior of these two compounds observed in the same conditions of milling (ball-to-powder ration, rotation speed) indicates that Gallium plays an accelerator role in the amorphization process. Taken into account the very low melting point of Gallium (29.76 °C) and the transformation of the mechanical energy into a thermal one during milling, the melting of Gallium may be supposed, acting as a liquid medium which facilitates the diffusion of elements. The very fast amorphization of the ternary system could be explained by both a local melt-quenching of elements and their progressive diffusion during impacts.
3.2. X-ray diffraction XRD analyses have been performed on the powder extracted all along the milling process, as presented in Fig. 2. In both cases, GeSe4 and 80GeSe2–20Ga2Se3, diffraction pattern corresponding to Germanium has only been observed. Selenium and Gallium react relatively fast forming an amorphous powder. Completely amorphous powders have been obtained after 110 h of milling in the case of GeSe4 composition and after 50 h for 80GeSe2–20Ga2Se3. This result is in complete agreement with the evolution of the color of the two compounds, which has already pointed out the much faster interaction of Germanium and Selenium in the presence of Gallium.
a)
1h
10 h
b)
0h
30 min
30 h
5h
3.4.1. GeSe4 Raman spectroscopy has been used in order to study the structure of the completely amorphous powder. In Fig. 3, three bands can be identified at 195 cm− 1, 215 cm− l and 260 cm− 1. The band at 195 cm−1 corresponds to the A1 breathing mode of corner-sharing (CS) GeSe4/2 tetrahedral units and the band at 215 cm−1 is associated to the Ac1 breathing like motions (companion peak) of edge-sharing (ES) GeSe4/2 units [16–18]. The difference in the intensities of these bands indicates that the structure of the amorphous material is mainly based on CS tetrahedral units while ES units are presented in a small quantity. The third band at 260 cm−1 corresponds to the A1 and E2 modes of Se–Se bonds from chains or cycles constituted of Se atoms [16–19]. This peak indicates the presence of Selenium-rich phases in the final structure of GeSe4 glass. A comparison between this spectrum and the one corresponding to the same glass made by the melt-quenching method has also been done. The same bonds are observed on both spectra indicating that the same structure is reached in both materials synthesized using the two different methods. 3.4.2. 80GeSe2–20Ga2Se3 Spectra presented in Fig. 4 have been normalized according to the most intense band (200 cm−1). One can see that the interaction between the three elements occurs fast. Already after 1 h of milling, bands associated with GeSe4/2 units can be distinguished together with Se–Se and metal–metal interactions. With the increase of the milling time, the shape of spectra is not changing, only the intensity of bands is modified. Three areas can be identified on the Raman spectra: 75–150 cm−1, 150–230 cm−1 and 230–350 cm−1. In the first domain several distortional vibrations of Ge–Se or Se–Se bonds give such a broad band as in the case of GeSe4 composition [20,21]. In the second area an intense band centered at 200 cm−1 with two shoulders at 178 and 215 cm−1 can be distinguished. The peak at 200 cm−1 is associated with the A1 symmetric mode of CS GeSe4/2 units [20,21]. Two shoulders correspond respectively to the stretching of Ge– Ge bond in the ethane-like units (Se3/2)Ge–Ge(Se3/2) (178 cm−1) and
50 h
10 h
20 h
70 h
30 h
90 h
40 h
110 h
50 h
Fig. 1. Evolution of the color of the a) GeSe4 and b) 80GeSe2–20Ga2Se3 powder with the milling duration.
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
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a)
3
b) 110 h 90 h 70 h 50 h 30 h 10 h 1h Ge
50 h 40 h 30 h 20 h 10 h Ge
Fig. 2. XRD patterns of the a) GeSe4 and b) 80GeSe2–20Ga2Se3 powders obtained after different milling durations.
to the symmetric in phase stretching of ES tetrahedral units (215 cm−1) [20–22]. Between 230 and 350 cm−1, three bands of low intensity can be observed at 240, 260 and 300 cm−1. The band at 240 cm−1 has been assigned in previous articles to an out of phase stretching of Se–Se bond in ES GeSe4/2 tetrahedral units [20,22,23]. Two assignments can be proposed for the broad band centered at 260 cm−1. A strong band at 252 cm−1 observed in glassy Se has been assigned to the A1 stretching mode of Se8 ring molecules [20]. P. Nemec et al. have assigned a band at 268 cm−1 observed in Ge25Ga5Se70 and Ge30Ga5Se65 glasses to A1 modes of vibration of Se chains [20]. Low intensity peak registered at 300 cm−1 has been assigned to an asymmetric stretching of CS GeSe4/2 units [21]. According to Fig. 4, the intensity of the band associated with the Se– Se bond vibration (domain 250–290 cm−1) is decreasing while the milling time is increasing. This trend indicates that the quantity of Selenium interacting with metals is increasing. However, the broad signal around 250 cm−1 has not totally disappeared indicating that a Se-rich domain remains in the final structure of 80GeSe2–20Ga2Se3 glass.
3.5. 77Se NMR 3.5.1. GeSe4 77 Se solid state NMR has been used to analyze powder samples starting by the initial raw Selenium. As one can see in Fig. 5, the peak centered on 850 ppm and corresponding to Se–Se–Se interactions presents a relatively large FWHM. In this way commercial Selenium
GeSe4/2
used for the mechanical alloying appears to be clearly vitreous. At the beginning of milling, from 10 min to 30 h, a part of Selenium (δiso = 850 ppm) becomes crystalline and when the milling time increases, beyond 30 h, it goes back amorphous. Other crystalline phases formed in the very beginning of the milling are distinguished giving rise to sharp lines between 200 and 700 ppm. Those are different Gex–Sey crystalline phases containing Se–Se–Ge or Ge–Se–Ge signals. Even if a clear assignment is not easy due to the signal to noise ratio, these sets of sharp lines look like those of the crystalline β-GeSe2 [18]. These lines disappear for long milling time. Surprisingly, between 30 and 50 h of milling it is difficult to detect 77Se lines corresponding to Selenium bonded to Germanium. Then, during the last 60 h of milling, the peak corresponding to amorphous Selenium (Se–Se–Se) is decreasing while Se–Se–Ge/Ge– Se–Ge peak is increasing in a significant way, as shown in Fig. 6a. The milling process has been continued up to 185 h in order to observe the evolution of the Se–Se–Se lines and the way that Se atoms incorporate the Ge–Se network. After 110 h of milling a saturation threshold of Se bridging Ge is reached. This result is coherent with the Raman spectroscopic analysis and confirms previous observations of Se rich domains in GeSe4 glass, i.e. rings or longer Se chains [24–27]. Spectrum obtained for the completely amorphous powder was also compared with the curve obtained for glasses synthesized by conventional melt-quenching method at different temperatures (Fig. 6b). Both curves exhibit the same shape which attests that the same structure of the glassy systems is reached by two different techniques, melt-quenching and mechanical alloying. Furthermore, the peak corresponding to amorphous Se is rather lower in the case of GeSe4 synthesized by mechanical alloying. In that way mechanical alloying
Se-Se
GeSe4/2
Fig. 3. Raman spectra of GeSe4 glass synthesized by melt-quenching method and of the completely amorphous powder obtained by mechanical milling.
Fig. 4. Raman spectra of the powder obtained after 1, 3, 5, 7, 10, 20 and 50 h of milling (normalized regarding to the peak at 200 cm−1).
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
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Se-Se-Ge Ge-Se-Ge
Se-Se-Se
110 h 70 h 30 h
50 h
1h
30 h
30 min
1h
10 min 0 min (raw Se)
30 min 1500
500
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10 min 0 min (raw Se) 1500
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0
77Se
permits to incorporate more Se in the Ge–Se network, in a comparable manner to a quenching from a very high temperature. 3.5.2. 80GeSe2–20Ga2Se3 Fig. 7 presents 77Se NMR spectra registered from the raw initial Selenium and on the powder samples obtained after 10 min, 30 min, 1 h and 50 h of milling. As in the case of the binary system GeSe4, Selenium peak (Se–Se–Se, δiso = 850 ppm) becomes narrower after 10 min of milling showing a crystallization of the selenium. With increasing milling time, Selenium returns amorphous and the intensity of its peak is decreasing for the benefit of the second peak corresponding to the interactions between Selenium and the two metals (Se–Se–Ge, Ge–Se–Ge, Se–Se–Ga, Ga–Se–Ga, Ge–Se–Ga, δiso = 405 ppm) [23]. It is worthy to note that the second peak appears after only 30 min of milling confirming the rapid initiation of the interaction between all the elements. The comparison between spectra obtained for the completely amorphous powder and for a 80GeSe2–20Ga2Se3 glass synthesized by melt-quenching, confirms the obtainment of the same structure of samples (Fig. 8a). Indeed, the same shape of the spectra is observed. In addition, the deconvolution of the spectrum registered on the completely amorphous powder has pointed out the presence of
a)
50 h 70 h 90 h 110 h 135 h 185 h
1000 iso
500 77Se
77Se
0
(ppm)
-500
-1000
Fig. 7. 77Se NMR spectra of raw initial Selenium and of 80GeSe2–20Ga2Se3 powder samples obtained after 10 min, 30 min, 1 h and 50 h of milling.
-500
(ppm)
Fig. 5. 77Se solid state NMR spectra of initial raw Selenium and of GeSe4 powder samples obtained at different milling durations.
1500
iso
0
(ppm)
-500
amorphous Selenium which does not react with the other elements (Fig. 8b). Even if the respective contribution is low (4%), this result has also been observed using Raman spectroscopy and indicates the presence of Selenium-richer domains. These latter domains have also been observed in Selenium-rich glasses such as GeSe4 where the Se–Se–Se contribution is around 30–40% [24–27]. It is nevertheless quite surprising to detect amorphous Selenium in the glass composition 80GeSe2– 20Ga2Se3 (Ge23.53Ga11.76Se64.71) where the Se rate is much lower. 4. Conclusion Glassy powders of GeSe4 and 80GeSe2–20Ga2Se3 compositions have been obtained by mechanical alloying of metallic raw Germanium, Selenium and Gallium. The same thermal (Tg) and spectroscopic (Raman spectroscopy, 77Se NMR) characteristics have been observed for the completely amorphous powders that for the respective glasses synthesized by the melt-quenching method. Using the same conditions of alloying (speed rotation, ball-topowder ratio) the necessary milling time to obtain a completely amorphous powder has been shortened by a factor of 2 by adding Gallium to the Ge–Se system. The low melting point of Gallium (29.76 °C) is reached in the milling jar during alloying and the acceleration of the interaction between Ge and Se elements in the presence of Ga may be due to a localized and very fast melt-quenching phenomenon combined to a diffusion process of elements. For GeSe4, the crystallization of Selenium and of several Gex–Sey phases (very probably GeSe2) has been observed under the mechanical alloying. A much longer milling time was conducted to the amorphization
b)
Melt-quenching from 880°C Melt-quenching from 1100°C 110 h of milling
1500 1000 500 iso
77Se
0
-500
(ppm)
Fig. 6. 77Se solid state NMR spectra of a) GeSe4 powder samples obtained after 50, 70, 90, 110, 135 and 185 h of milling and b) GeSe4 powder (110 h of milling) and GeSe4 glasses synthesized by melt-quenching method.
Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015
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a)
50 h of milling Melt-quenching
b)
5
50 h ofmilling
Se-Se-Se
1800
1200
600 iso
77Se
0
-600
-1200
(ppm)
2000
1000 iso
77Se
0
-1000
(ppm)
Fig. 8. a) 77Se NMR spectra of the completely amorphous powder (50 h of milling) and of the 80GeSe2–20Ga2Se3 glass synthetized by melt-quenching method. b) Deconvolution of 77Se NMR spectrum of the 80GeSe2–20Ga2Se3 powder obtained after 50 h of milling.
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Please cite this article as: E. Petracovschi, et al., Structural study by Raman spectroscopy and 77Se NMR of GeSe4 and 80GeSe2–20Ga2Se3 glasses synthesized by mechanical milling, J. Non-Cryst. Solids (2015), http://dx.doi.org/10.1016/j.jnoncrysol.2015.04.015