Evidence of Silica Polymerization During Internal Nucleation of Glassy Lithium Disilicate
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experiments was better than 5 x 10-9 torr. The problem of charging effects due to a loss of expelled electrons was alleviated by using thin samples and by flooding the sample surface with an electron gun. Absolute peak position calibration was carried out by referencing to the C 1s signal (284.8 eV) from adsorbed CO 2 on the sample. Samples were slightly argon etched for a few minutes to remove surface contaminants after the C Is reference signal was detected. No changes were observed in the 0 Is and Li Is peak positions during sputtering. Gaussian curves were fitted according to a standard fitting routine to deconvolute the photoelectron peaks. The estimated error in peak position is less than 10 percent. RESULTS The binding energies and relative intensities of the 0 1s and Li Is spectra of all phases studied are collected in Tables I and II. Table I. 0 Is XPS binding energies (eV), FWHM (eV) and relative intensities (%) for crystalline and glassy lithium silicates and nucleated lithium disilicate. Compound Glass Li2Si2O5
Nucleation, h at 450*C 0
0.5 1.5 3.0 6.0
O(br), eV
I,%
FW-HM, eV
531.2
75.6
93.8 96.4 97.3 93.5
2.1 2.0 1.8 1.9
1.9
529.2
532.0 531.7 531.8 531.8
I,%
O(nbr), eV 529.7 529.7 529.7 529.9
FWHM, eV
24.2
2.2
6.2 3.6 2.7 6.5
1.9 1.8 1.5 1.5
Crystalline Li2Si2O5
----
532.5
74.6
1.8
530.7
25.4
1.7
Li2SiO3
-------
532.4
56.2
1.9
----
--..
-.-.
530.8 531.4
43.8 100
1.9 2.1
Li4SiO4
Table II. Li 1s XPS binding energies (eV), FWHM (eV), and relative intensities (%) for crystalline and glassy lithium silicates and nucleated lithium disilicate. Compound Glass Li2Si2O5
Crystalline Li2Si2O5 Li2 SiO 3 Li4SiO4
Nucleation, h at 450*C
Li, eV
I,%
FWHM,eV
Li, eV
I,%
0
55.11
100
2.0
---
0.5 1.0 1.5 2.0 6.0 200
55.2 55.2 55.2 55.2 55.2 55.3
65.3 44.5 50.2 49.5 73.5 88.6
1.9 2.0 2.0 2.0 2.2 2.2
51.7 51.6 51.7 51.6 51.7 51.5
34.7 55.5 49.8 50.1 26.5 11.4
----.--.--
55.3 55.2 55.1
100 100 78.4
1.8 1.8 2.0
-----
.......
51.8
21.6
240
FWHM,eV 2.0 2.0 2.0 2.0 2.2 2.2
----...
2.0
V
3
-,A
o"o
.
C,3> 03)
'oos
C-)
(4. "s 020
en
0
.11 0i'-S'
0'0
.,, 0 Cý
241
5
Figures 1 and 2 show the observed spectra from which the data in Table I and II were taken. Inspection of these tables and figures show that the 0 1s spectra for crystalline and glassy lithium disilicate are similar in shape but shifted in position with respect to one another. The crystalline diand metasilicate 0 Is peak positions are similar, whereas the 0 Is peak position for the orthosilicate occurs at a position between the two other crystalline lithium silicates. Notice the 0 1s and Li Is spectra of nucleated Li disilicate glass. In the 0 Is spectrum of glassy lithium disilicate two peaks in the proper 3 to 1 ratio are present for O(br) and O(nbr). After nucleation the intensity of the O(nbr) peak decreases substantially whereas the O(br) peak shifts about 0.5 eV to smaller binding energy. In the Li Is spectrum the glass spectrum before nucleation shows one peak. After heat treatment
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