A study of glass structure in Li2OSiO2, Li2OAl2O3SiO2 and LiAlSiON systems

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Journal of Non-Crystalline Sohds 112 (1989) 80-84 North-Holland, A m s t e r d a m

A STUDY OF GLASS STRUCTURE IN Li20-SiO2, Li20-Al203-SiO 2 AND L i - A I - S i - O - N SYSTEMS t XU Xiaojie, LI Jiazhi and YAO Luping Shanghai Institute of Ceramics, Academia Sinica, Shanghai, PR China

The structures of Li20-SiO2, L i 2 0 - A 1 2 0 3 - S i O 2 and L i - A 1 - S i - O - N glasses were studied by m e a n s of R a m a n spectroscopy, IR spectroscopy, X-ray fluorescence spectroscopy and X-ray photoelectron spectroscopy. The distribution of Li + and non-bridging oxygen ions, the structural state and distribution of A1 and N ions in glass as well as their effects on the glass network structure are discussed.

1. ~ u ~ o n

The physical and chemical properties of Li-contalning silicate glasses are special in many aspects compared with other alkali-containing silicate glasses. The tendency for phase separation and crystallization of Li-containing glasses makes them important in the manufacture of glass-ceramics [1]. We believe that the investigation of glass structure is helpful for deepening our understanding of glass physical chemistry. It is, therefore, of interest to investigate the structure of Li20-containing glasses. In this study, Raman, IR, X-ray fluorescence and X-ray photoelectron spectroscopy were used to investigate the structure of Li20-SiO 2, L i 2 0 ml203-SiO 2 and Li-A1-Si-O-N glass systems. On the basis of studies of the structural characteristics of Li20-SiO 2 glasses, the present paper primarily deals with the effects of the introduction of A1 and N ions on the glass structure.

2. Experimental and results

2.1. Sample preparation Four Li20-SiO 2 glasses were melted. The glass composition 24Li20-76SiO 2 (No. 040) was i Project supported by the Science Fund 5860355 of the National Natural Science Foundation of China. 0022-3093/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

selected as the base glass. Li20-A1203-SiO 2 and L i - A 1 - S i - O - N glasses were prepared by introducing A1203 and A1N into the base glass. Glass compositions are listed in table 1. Oxide glasses were prepared from reagent grade raw material. The glasses were melted at 14001500 °C in a Pt crucible; during melting the melts were stirred with a Pt stirrer for fining and homogenization. The homogeneous mixtures of 040 glass

Table 1 Glass compositions (the glass composition error is within

+0.5~) Sample No.

Glass composition (mol%) Li20

SiO 2

LS 2 010 020 040

33.3 31.0 29.0 24.0

66.7 69.0 71.0 76.0

041 042 043 044 045 046 047

23.5 23.1 22.6 21.4 20.3 19.4 18.4

74.5 73.1 71.7 67.9 64.4 61.3 58.5

140 240

24.6 25.3

74.0 72.0

141 242 343

23.1 22.2 21.4

73.1 70.4 67.9

A1203

Si3N 4

AIN

2.0 3.8 5.7 10.7 15.3 19.3 23.1 1.4 2.7 3.8 7.4 10.7

Xu Xiaofie et al. / Structure of Li 20-Si02, Li eO-AI 203-SiO2 and Li-AI-Si-O-N

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s p o n d i n g to these R a m a n b a n d s for the glasses s t u d i e d in this w o r k are listed in t a b l e 2 [2,3]. T h e I R a b s o r p t i o n s p e c t r a of the glasses were also m e a s u r e d using the K B r pellet technique. It was o b s e r v e d t h a t the I R s p e c t r a of these glasses a p p e a r e d to b e n e a r l y i n d e p e n d e n t of glass c o m position. "&

2.2.2. Results of X-ray fluorescence and X-ray photoelectron spectroscopy experiments T h e c o o r d i n a t i o n o f A13+ ions was d e t e r m i n e d q u a n t i t a t i v e l y b y m e a s u r i n g the c h e m i c a l shifts of the A 1 K , lines of the glasses. T h e d e t a i l e d experim e n t a l m e t h o d has b e e n d e s c r i b e d p r e v i o u s l y [4]. T h e results o f the X R F e x p e r i m e n t s showed that in these glasses m o s t of the A1 ions are in 4-coord i n a t i o n , o n l y a s m a l l a m o u n t of AI ions are in 6-coordination.

4~

Table 2 Band frequencies and vibrational mode assignments for the glasses studied in this paper

SiO: glass 300

500

700

900

1100

1300

llaman S h i f t (e.m-1)

Fig. 1. Raman spectra of some Li 20-SiO 2 glasses.

p o w d e r with A I N p o w d e r were m e l t e d in a M o crucible in a N 2 a t m o s p h e r e at 1600 ° C b y i n d u c tion h e a t i n g to p r e p a r e o x y n i t r i d e glasses.

2.2. Experimental results 2.2.1. Raman spectra of glasses T h e R a m a n s p e c t r a of these L i 2 0 - S i O 2 , L i E O - A I 2 0 3 - S i O 2 a n d L i - A 1 - S i - O - N glasses are illustrated in figs. I a n d 2 a n d 3, respectively. I n o r d e r to s t u d y the v a r i a t i o n s o f glass s p e c t r a w i t h glass c o m p o s i t i o n s m o r e clearly, the high f r e q u e n c y envelopes in the range 900 to 1300 c m -1 were d e c o n v o l u t e d into i n d i v i d u a l b a n d s w i t h a G a u s sian lineshape, the m e a n square d e v i a t i o n of dec o n v o l u t i o n is within _+2%. T h e d e c o n v o l u t i o n results are shown in the figures directly. T h e s t r u c t u r a l groups a n d v i b r a t i o n a l m o d e s corre-

Band frequency (cm -1)

Assignment a)

440 vs b) 490 s(sh) 606 m 800 m 1050 w 1200 vw

vs (Si-O-Si) 6-membered rings Ps (Si-O-Si) 4-membered tings defect ~8 (Si-O-Si) ~as (Si-O-Si) TO mode Vas (Si-O-Si) LO mode

Glassesstudied in thispaper Band frequency (cm- 1)

Assignment

470 522 570 800 950 1040 1100 1200

~s (T-O-T) 6-membered rings characteristic Raman band of Si 2ON2 us (T-O-T) (Si205) or (Si206) species p (T-O-T) ~s ( S i - O - ) Q2 species Pas (T-O-T) (see discussion) ~'s ( S i - O - ) Q3 species ~ (T-O-T) (see discussion)

a) T, glass forming cation; us (T-O-T), symmetric stretching motion of Ob in T - O - T linkage; ~as (T-O-T), antisymmetric stretching motion of Ob in T - O - T linkage; Ps (T-O-T), see ref. [3]; vs (Si-O-), stretching vibration of Si-O- bond. b) Abbreviations: vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder.

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Xu Xiaojie et al. / Structure of Li20-Si02, LieO-AI203-SiO 2 and Li-AI-Si-O-N

1°9°)

-\oo 4~ n-I

/A i

I

300

I

[

500

I

l

I

i

i

700 900 Ii0O ~amm. Shift (Cm-I}

l

13oo 300

500 70o 900 11oo ~am-~ Shift (em-I}

Fig. 2. Raman spectra of glasses on the join 24Li 20-76SIO2-A1203

The O l s photoelectron spectra of the glasses were measured to study the structural state of oxygen. The experimental methods are described in detail in the literature [4]. The O l s envelopes of these glasses were deconvoluted into two individual bands with a Gaussian lineshape to represent the two types of oxygen, O b (bridging) and O n b (nonbridging), respectively. The mean square deviation of deconvolution is within _ 1%. The relaTable 3 The measured and theoretically estimated distribution of Onb and O b in some glasses (in %). The experimental error is reasonably estimated to be within + 5% Sample No.

LS2 glass 040 240 043

Distribution of O,b and O b Measured Theoretically estimated Onb

0 b

Onb

0 b

39 27.5 31 26

61 72.5 69 74

40 27 29 27

60 73 71 73

13oo

.

tive area of these b a n d s reflected the relative concentrations of O b and Onb [5]. The results of the distribution of O b and Onb as measured by XPS are listed in table 3. It can be seen that the experimental values are in good agreement with the theoretically estimated values. In the calculation of the theoretically estimated values, A1 ions were supposed to be in 4-coordination connecting Onb and N ions to exist in the form of "three-bridging nitrogen" (connected with three Si(O, N) 4 tetrahedra).

3. Discussion 3.1. The structure o f L i 2 0 - S i O 2 glasses

According to the experimental results, it was f o u n d that in these L i 2 0 - S i O 2 glasses SiO4 tetrahedra coexist in three forms: Q4, Q3 and Q2 (the subscripts indicate the n u m b e r of O b in a SiO 4 tetrahedron), which correspond to the 470, 1100

83

Xu Xiaojie et al. / Structure of Li 20-Si02, Li 20-AI203-SiO 2 and L i - A I - S i - O - N i

t

i

J2

I

~00

[

500

I

i

,

I

700

i

I

i

I

i

I

900

I

I

1100

'

I

1300

Raman Shifg (era-I)

Fig. 3. Raman spectra of some Li-A1-Si-O-N glasses.

and 950 cm -1 bands in the Raman spectra of these glasses, respectively. Since the Li 2° contents in these glasses are all less than 33.3 mol%, the presence of Q2 groups indicated that the distribution of O~b in these glasses was non-random or inhomogeneous, i.e. Li + and Onb ions clustered into regions of high Li20 content, and consequently led to the presence of extended highly polymerized silica-like structural clusters correlated with the appearence of the 470 cm-~ band. 3.2. The structure of L i 2 0 - A l 2 0 7 S i O 2 glasses The results of XRF and XPS experiments showed that A13+ ions were mainly 4-coordinated connecting Onb in these glasses. This appeared in the glass Raman spectra in that the intensities of the 570, 950 and 1100 cm -1 bands, which represented the presence of Onb in glass structure, decreased with increasing AI203 content. Meanwhile the glass structure tended to be more polymerized.

The deconvolution results of the high-frequency envelopes in the Raman spectra of these AI203containing glasses further showed that as the A1203 content increased the intensity of the 950 cm -1 band corresponding to the Q2 structural group decreased more rapidly than that of the 1100 cm -1 band corresponding to the Q3 group. This indicated that the introduction of A1203 made the distribution of Onb in glass more random. In the high-frequency region of the L i 2 0 A1203-SiO 2 glass spectra, the two bands near 1040 and 1200 cm -1 were considered to be due to the non-symmetric stretching vibration of O b in T - O - T linkages (~'as(T-O-T), where T represents the network forming cations, A1 and Si) [3,7]. As was shown in fig. 2, in the Al203-free 040 glass, the intensity of the 1040 cm -~ band was far stronger than that of the 1200 cm -a band, we therefore thought it valid to suppose that the 1040 cm-1 band corresponds to the Vas(T-O-T) vibration of the weaker silicate network [6-8]. Because the A1-O bond is weaker than the Si-O bond, the position of these two bands due to the Vas(T-O-T ) vibration will shift to lower frequency with increasing the number of A1-O bonds in the glass network. Adding A1203 to 040 glass, the band near 1040 c m - a shifted to a lower frequency and its intensity increased, but the frequency and intensity of the 1200 cm -1 band were nearly unchanged when the A1203 content was small. On further increasing the AI203 content the 1200 cm -1 band shifted to lower frequency and its intensity increased rapidly. Thus, on the basis of supposing that the Raman band near 1040 cm -~ corresponds to the weaker aluminosilicate network, we inferred that A13+ ions preferred to be incorporated into the regions of high Li20 content, and consequently they were partly clustered as well, i.e. A13 + ions preferred to form (-Si-(0A1)) structural groups. With further increasing A1203 content, (=Si-OA1) structural groups appeared resuiting in the change of the frequency and intensity of the Raman band near 1200 cm -a. 3.3. The structure of L i - A I - S i - O - N

glasses

The results of X R F and XPS experiments showed that A13 - ions were also mainly in 4-coor-

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Xu Xiaojie et al. / Structure of Li20-Si02, Li20-AleOz-SiO 2 and L i - A I - S i - O - N

dination and nitrogen atoms mainly existed in the form of "three-briding nitrogen" in the oxynitride glasses. The introduction of nitrogen resulted in a significant change of the glass Raman spectra. Firstly, the intensities of all those Raman bands that had appeared in the Raman spectrum of 040 glass greatly decreased with increasing nitrogen content. This made it difficult to study the glass structure changes resulting from the introduction of nitrogen in detail. The IR spectra of these glasses were nearly independent of the introduction of A1N and A1203, this indicated that the main structural characteristic of the oxynitride glasses was still a continuous random network constituted with SiO 4 tetrahedra. To analyze the Raman spectra of these oxynitride glasses in detail, it was found that the intensity ratio of the 950 to the 1100 cm -1 band (195o/111oo) increased with increasing nitrogen content. This indicated that the distribution of Onb tended to be more non-random. Secondly, the other marked feature characteristic of the Raman spectra of these oxynitride glasses is the sharp and intense Raman band at 522 cm -1, which is the characteristic band of Si2ON 2 crystal. The appearance of this 522 cm -a band showed that nitrogen atoms were also clustered locally so as to form Si 2 O N 2 crystallites in these oxynitride glasses. Transmission electron microscopy and selected area electron diffraction experiments also demonstrated the presence of Si2ON 2 crystallites, which are uniformly dispersed in these oxynitride glasses.

4. Conclusions (1) In the L i 2 0 - S i O 2 glasses, the Li and O,b ions have a greater tendency to cluster into regions of high Li2 ° content. (2) Adding A1203 to L i 2 0 - S i O 2 glasses, A13+ ions are mainly in 4-coordination, connecting with Onb to make the glass structure more polymerized. Moreover, A13+ ions prefer to be incorporated into the regions rich in Li + and Onb ions and lead to a more random distribution of O,b in the glass network. Consequently the distribution of A13+ ions in glass is also non-random. (3) In L i - A 1 - S i - O - N glasses, A13+ ions are also mainly 4-coordinated and nitrogen atoms exist in the form of "three-bridging nitrogen" to produce a more cross-linked and more compact glass network, and also to make the distribution of Onb more non-random. Nitrogen atoms are also clustered locally so as to form Si2ON 2 crystallites in these oxynitride glasses.

References [1] P.W. McMillan, Glass Ceramics, 2nd ed. (Academic Press, London, 1979). [2] D.W. Matson et al., J. Non-Cryst. Solids 58 (1983) 323. [3] S.K. Sharma et al., J. Non-Cryst. Solids 68 (1984) 99. [4] Xu Xiaojie, PhD Thesis, Shanghai Institute of Ceramics, Academia Sinica (1988). [5] V.R. Brtickner et al., Glastechn. Bet. 51 (1978) 1. [6] P. McMillan et al., Geochim. Cosmochim. Acta 46 (1982) 2021. [7] B.O. Mysen et al., Am. Mineral. 70 (1985) 88. [8] S.K. Sharma et al., Am. Mineral. 68 (1983) 113.