ISSN 00360236, Russian Journal of Inorganic Chemistry, 2014, Vol. 59, No. 3, pp. 255–258. © Pleiades Publishing, Ltd., 2014. Original Russian Text © O.N. Koroleva, M.V. Shtenberg, P.V. Khvorov, 2014, published in Zhurnal Neorganicheskoi Khimii, 2014, Vol. 59, No. 3, pp. 402–405.
PHYSICAL METHODS OF INVESTIGATION
Vibrational Spectroscopic and Xray Diffraction Study of Crystalline Phases in the Li2O–SiO2 System O. N. Koroleva, M. V. Shtenberg, and P. V. Khvorov Institute of Mineralogy, Ural Branch, Russian Academy of Sciences, Miass, Chelyabinsk oblast, 456317 Russia email:
[email protected] Received August 5, 2013
Abstract—xLi2O ⋅ (100 – x)SiO2 phases, where x = 20, 25, 33, 40, 50, 55, and 60 mol % (hereinafter, Li20, Li25, Li33, Li40, Li50, Li55, and Li60) were crystallized from melts, and their qualitative composition was determined by Xray diffraction. The Li6Si2O7 phase was established to precipitate during the crystallization of the melt containing 60 mol % Li2O, thus enabling us to locate characteristic bands in the IR and Raman spectra of lithium pyrosilicate. DOI: 10.1134/S0036023614030139
Silicate systems are the most important oxide glass formers and widely spread in geological objects, so their study is equally significant for both the optimiza tion of industrial technologies and geochemical inves tigations. The lithium silicate system is well studied in the region of low lithium contents by vibrational spec troscopy, Xray diffraction, calorimetry, and thermal analysis [1–3] in contrast to xLi2O ⋅ (100 – x)SiO2 melts, glasses, and crystalline phases with x ≥ 50, which are the objects of contemporary studies. EXPERIMENTAL Silicates were synthesized from amorphous SiO2 (pure for analysis grade) and lithium carbonate Li2CO3 (chemically pure grade). The batch was care fully mixed with alcohol in a mortar, dried, and melted in a platinum crucible inside a silicon carbide furnace at a temperature of up to 1523 K until the melt was completely homogenized. To obtain crystalline phases, the sample was annealed in the furnace. The Raman spectra of glasses and crystalline phases were recorded on an iHR 320 Horiba Jobin Yvon spectrom eter with an Olimpus BX41 microscope. The IR trans mission spectra of crystalline phases were recorded on a Nexus870 Thermo Nicolet Fouriertransform IR spectrometer by the standard technique (as KBr pellets). The baseline correction procedure was performed for all recorded spectra. The spectra were processed using the OMNIC Thermo Nicolet software suite. The transmis sion spectra were converted into absorption spectra (absorbance). Crystalline phases were studied by Xray diffraction on a DRON2.0 diffractometer (CuKα radia tion, graphite monochromator).
RESULTS AND DISCUSSION Figure 1 shows the Raman spectra of crystallization products for the studied compositions of the lithium silicate system are compared with the spectrum of pure αquartz (hereinafter, Li0). The lowfrequency band in the Raman spectrum of quartz at 464 cm–1 corresponds to the vibrations of bridging oxygen atoms in the silicon–oxygen tetrahe dron. At 20 mol % Li2O, the intensity of this band in the Raman spectrum of the crystalline phase decreases, and new bands with maxima at 550 and 1111 cm–1 appear. The band at ~550 cm–1 corresponds to the symmetric stretching and partially bending vibrations of Si–O–Si bridges [4, 5]. The bands in the highfrequency region of the Raman spectrum of sili cate systems are produced by the vibrations of terminal groups in SiO4 tetrahedra with different ratios of bridging and nonbridging oxygen atoms [6, 7]. The spectra of crystalline phases of the samples containing 20 and 25 mol % Li2O exhibit the only major highfrequency band corresponding to the vibrations of Si–O bonds in Q33 tetrahedra with three bridging oxygen atoms at ~1111 cm–1 [8]. The same band is observed in the Raman spectrum of the crystal contain ing 33 mol % Li2O and dominates against the back ground of a weak peak, which appears at ~1043 cm–1 and may be assigned to the vibrations of Q32 structural units representing tetrahedra with three bridging oxy gen atoms bonded to Q2 tetrahedra [8]. The dominant bond with a maximum at 980 cm–1 in the Raman spec trum of the crystalline phases obtained from the melts containing 40, 50, and 55 mol % Li2O is produced by the vibrations of Q22 structural units, and the band with a maximum at ~ 850 cm–1 is due to the vibrations of Q11 structural units representing a dimer moiety [8]. The weak band corresponding to the vibrations of Q32
255
256
KOROLEVA et al. I
A 464 1086 356
Li0 Li0
466 416 360
1111
557
Li20 979
416 1112
547 362 470
1087
Li25
1043
Li33
Li40
980
361 849
1032
951
Li40
979 1082
985
614 853
Li50
1037 Li50
960 981 1082
Li55
964 982
985
615 829 807 855
1038
611
Li55 1076
823 357
Li25
941 979
608
366
1087
1112
418 557 361 471
364
950
807 885 983 951 1036 683
Li60
Li60 300 400 500 600 700 800 900 100011001200 Δν, cm–1
400 500 600 700 800~ 900–11000 1100 1200 ν, cm
Fig. 1. Raman spectra of xLi2O ⋅ (100 – x)SiO2 crystalline phases, where x = 0, 20, 25, 33, 40, 50, 55, and 60.
Fig. 2. IR absorption spectra of the crystalline phases formed under the cooling of xLi2O ⋅ (100 – x)SiO2 melts, where x = 0, 25, 40, 50, 55, and 60.
tetrahedra is also observed at ~1032 cm–1. At a lithium oxide content of 55 mol %, a new band with a maxi mum at ~829 cm–1 appears in the spectrum, thus indi cating the existence of Q1 type tetrahedra bonded to Q2 structural units. When the lithium oxide content increases further up to 60 mol %, the band at ~823 cm–1 becomes dominant, thus indicating the further depo lymerization of the silicate network, as the modifying ion content increases, to consist now predominantly of Q1 type tetrahedra. In this case, Q22 (band at ~983 cm–1) and Q0 (shoulder at ~807 cm–1) tetrahedra are present in the crystalline phase.
The IR spectra of crystalline phases in the Li2O– SiO2 system with various compositions are shown in Fig. 2. The stretching and bending vibrations of the crystal lattice and Si–O–Si bonds appear in the low frequency region of the spectrum (400–800 cm–1), so that the change in the lithium oxide content does not appreciably change the positions of the bands. How ever, the bands in the spectra of the crystalline lithium silicate phases have considerable shifts in comparison with the spectrum of quartz, and this may be explained by their different crystal structures. In the highfrequency region of 900–1200 cm–1, the IR spectra of the studied lithium silicates have
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 59
No. 3
2014
VIBRATIONAL SPECTROSCOPIC AND XRAY DIFFRACTION STUDY
obvious distinctions: the intensities of bands in the region of 950–980 cm–1 are redistributed, may be, due to the dominance of the vibrations of different struc tural units in different phases. The intensity of the band at ~1080 cm–1 is reduced with increasing lithium oxide content, thus indicating a decrease in the con tent of Si–O–Si bonds and, consequently, the depoly merization of the initial melt. The positions of major IR and Raman bands in the spectra of the crystalline phases formed from lithium silicate melts Li25, Li33, Li40, Li50, Li55 and Li60 are given in the table. The samples were also characterized by Xray dif fraction (Fig. 3). After the existing phases were identi fied, their approximate ratios were calculated by the method of constant coefficients with the use of “corundum numbers” taken from the cards that had the most complete diffraction correspondence with the phases obtained by us. Only lithium metasilicate Li2SiO3 was detected in the sample where the lithium oxide content was 50 mol %, and Li2SiO3 (~90%) and Li4SiO4 (~10%) were found at 55 mol % Li2O. The shape of the diffraction curve for the 60Li2O ⋅ 40SiO2 composition indicated the presence of an Xray amor phous phase, which is not considered in this work. Li2SiO3 (~40%), Li4SiO4 (~45%), and Li6Si2O7 (~15%) were detected in the crystalline phase. From the Xray diffraction data and the Raman spectra, it is obvious that only lithium metasilicate crystallizes from the melt containing 50 mol % Li2O as in the sodium silicate system [6, 8], thus agreeing with the phase diagram [13]. Lithium metasilicate and orthosilicate form a eutectic at 1024°C and 60.2 mol % Li2O, so the formation of a small amount of lithium orthosilicate is observed when the content of Li2O increases to 55 mol %, thus agreeing with the appear ance of new peaks in the Raman spectrum (807 and 829 cm–1). However, the Raman spectrum of sample Li60 contains additional bands (683, 885, and 951 cm–1), which may belong to lithium pyrosilicate, in addition to the bands assigned to lithium meta and orthosili cate crystals . According to [13], a thermal effect, which may be due to the solidphase formation of Li6Si2O7, is observed at 60 mol % Li2O. These data agree with reported results [2], where the feasibility to synthesize metastable lithium pyrosilicate was shown and the unit cell parameters of its crystals were deter mined. Comparing the Raman spectra of sodium meta, ortho, and pyrosilicates [6, 8] with the spec trum of Li60, one can suppose that the latter may be the superposition of the spectra of lithium meta, ortho, and pyrosilicates (Fig. 4). It is obvious that more considerable depolymerization at a lower con tent of the modifying cation is typical for the lithium silicate system in contrast to the sodium silicate sys tem, and this is explained by the smaller size of a lith ium atom. RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
257
Assignment of bands observed in the spectra of lithium sili cates Band position, cm–1 IR
410 450 525 610
Assignment
Source
Raman 360 Lattice vibrations, Li–O bond [4, 9, 10] vibrations, and Si–O–Si bond 410 bending vibrations 465 525 Symmetric stretching and partial [4, 5] 560 ly bending vibrations of Si–O–Si bridges 610
740 790
Bending vibrations of Si–O–Si bridges
[4]
825 Q0 850
850 Q11
[9]
21
940 Q 980
985 Q22
[9]
32
1035 Q 1080
Si–O–Si stretching vibrations 1110
Q3
[9] [11, 12]
Hence, the crystallization of solid phases according to the phase diagram [14] is observed as the content of lithium oxide in an initial silicate melt increases. The precipitation of a small amount of lithium pyrosilicate is observed for composition Li60; the characteristic I
Li50
Li55
10
20
30
40 2θ, deg
50
Li60 60
Fig. 3. Xray diffraction patterns of crystalline samples Li50, Li55, and Li60. Vol. 59
No. 3
2014
258
KOROLEVA et al.
the Li2O–SiO2 system and the physicochemical prop erties of lithium pyrosilicate.
I
Na50
ACKNOWLEDGMENTS This study was supported by the Russian Founda tion for Basic Research (project no. 120500294a), a grant of the President of the Russian Federation for young scientists (grant no. MK6284.2013.5), the Federal Target Program “Research and Research Training Resources for Innovative Russia,” and a grant of the Ural Branch of the Russian Academy of Sci ences for young scientists. REFERENCES
Na60
Na67
Li60 500
600
700
800 900 1000 1100 1200 Δν, cm–1
Fig. 4. Raman Spectra of crystalline silicates Na50, Na60, Na67 [5], and Li60.
peaks in the Raman spectra of the pyrosilicate were determined form the common spectrum of the crystal line phase. The obtained data agree with the results of phase equilibria [1, 2] and may be an object of further studies that would be intended to revise the diagram of
1. A. Meshalkin and A. Kaplun, Cryst. Growth 275, 115 (2005). 2. S. Claus, H. Kleykamp, and W. SmykatzKloss, Nucl. Mater. 230, 8 (1996). 3. N. Umesaki, N. Iwamoto, M. Tatsumisago, and T. Minami, NonCryst. Solids 106 (1), 77 (1988). 4. T. Furukawa, K. E. Fox, and W. B. White, Chem. Phys. 75, 3226 (1981). 5. V. N. Bykov, V. N. Anfilogov, and A. A. Osipov, Spec troscopy and Structure of Silicate Melts and Glasses (Inst. of Mineralogy, Miass, 2001) [in Russian]. 6. V. N. Anfilogov, V. N. Bykov, and A. A. Osipov, Silicate Melts (Nauka, Moscow, 2005) [in Russian]. 7. B. O. Mysen and J. D. Frantz, Contrib. Mineral. Petr. 117 (1), 1 (1994). 8. O. N. Koroleva, V. N. Anfilogov, A. Shatskii, and K. D. Litasov, NonCryst. Solids 375, 62 (2013). 9. S. A. MacDonald, C. R. Schardt, D. J. Masiello, and J. H. Simmons, NonCryst. Solids 275 (1), 72 (2000). 10. M. Nocun and M. Handke, Mol. Struct. 596 (1), 145 (2001). 11. J. L. You, G. C. Jiang, H. Y. Hou, et al., Raman Spec trosc. 36, 237 (2005). 12. H. Krüger, V. Kahlenberg, and R. Kaindl, Solid State Chem. 180 (3), 922 (2007). 13. B. O. Mysen and J. D. Frantz, Chem. Geol. 96, 321 (1992). 14. A. RomeroSerrano, C. GomezYanez, M. Hallen Lopez, and J. AraujoOsorlo, Am. Ceram. Soc. 88, 141 (2005).
Translated by E. Glushachenkova
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 59
No. 3
2014
