Vibrational study of thermally ion-exchanged sodium
aluminoborosilicate glasses
E. Stavrou
a,
⁎, D. Palles
a
, E.I. Kamitsos
a
, A. Lipovskii
b
, D. Tagantsev
b
, Y. Svirko
c
, S. Honkanen
c
a
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 116 35 Athens, Greece
b
Saint Petersburg State Polytechnical University, Polytechnicheskaja 29, Saint Petersburg 195251, Russia
c
Institute of Photonics, University of Eastern Finland, Yliopistokatu 7, FI-80101 Joensuu, Finland
abstract article info
Article history:
Received 13 September 2013
Received in revised form 19 November 2013
Available online xxxx
Keywords:
Ion-exchange;
Glass structure;
Infrared;
Raman
Thermally ion-exchanged M
+
-for-Na
+
(M = K and Ag) aluminoborosilicate glasses were obtained from the
glass (SiO
2
)
60
(B
2
O
3
)
10
(Al
2
O
3
)
6
(Na
2
O)
20.2
(ZrO
2
)
3.7
(Sb
2
O
3
)
0.1
(in mol%) and studied by infrared reflectance and
micro-Raman spectroscopy. The results of both techniques are consistent with local structural rearrangements
induced by ion-exchange below glass transition temperature, T
g
, and are expressed for the silicate network by
the chemical equilibrium Q
2
+ Q
4
⇔2Q
3
where Q
n
represents a silicate tetrahedron with n bridging oxygen
atoms. Replacement of Na
+
by K
+
was found to shift this equilibrium to the right, while the introduction of
Ag
+
ions causes the opposite effect. Micro-Raman depth profiling showed that these structural changes occur
within a layer whose thickness depends on the type of the guest cation and the conditions of ion-exchange;
the thickness is about 50 μm for Ag
+
ions exchanged at 340 °C for 180 min and about 40 μm for K
+
exchanged
at 325 °C for 6 h.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Ion-exchange below glass transition temperature is a well known
technique to modify the mechanical [1–3] and optical [4–6] properties
of glasses. Typically, a sodium silicate glass is submersed in a bath con-
taining a molten salt (e.g. KNO
3
) at elevated temperatures. Due to differ-
ences in chemical potential, Na
+
cations from the glass will migrate to
the molten salt bath while an equal number of guest cations from the
molten salt will replace the migrating Na
+
ions. When the guest cations
are larger than sodium, for instance when K
+
is substituted for Na
+
, this
replacement causes the glass surface to be in a state of compression
[1–3] (chemical pressure) that may reach several hundreds of MPa,
thus leading to the chemical strengthening of glass. The optical proper-
ties of glass are also altered when Na
+
ions are substituted by more
polarisable (e.g. Ag
+
) ions. Such a local modification of the refractive
index can be used for developing waveguides, micro-optics, etc.
Despite the technical applications of ion-exchange there are still
open questions concerning its mechanism at the molecular level, in-
cluding the possibility for structural changes induced by ion-exchange
below T
g
. Such changes would allow for the accommodation of guest
cations in a network suited initially for the host cations and would man-
ifest the ability of glass to modify its local structure even below T
g
,
where the network structure is generally considered to be unaffected
by ion-exchange (see, for example, Ref [5]).
In order to address these issues, we have carried out a combined in-
frared reflectance and micro-Raman spectroscopy study on two glasses
derived from the glass (in mol%) (SiO
2
)
60
(B
2
O
3
)
10
(Al
2
O
3
)
6
(Na
2
O)
20.2
(ZrO
2
)
3.7
(Sb
2
O
3
)
0.1
(Na-glass hereafter) by thermally ion-exchanging
K
+
-for-Na
+
(K-glass) and Ag
+
-for-Na
+
(Ag-glass). The aim of this
work is to search for correlations between the type/penetration depth
of the guest cations and possible structural changes induced by ion-
exchange. The spectroscopic results show unambiguously that ion-
exchange induces local changes in glass structure; they are manifested
mainly by rearrangements in the silicate tetrahedral units Q
n
even at
temperatures below T
g
and depend directly on the nature of the guest
cations which replace the sodium host cations in the Na-glass.
2. Experimental
2.1. Sample preparation
The Na
+
-glass was synthesized at 1560 °C by melting an appropri-
ate 150-g batch in silica crucible for 2 h, including 90-min of melt stir-
ring. The starting reagents were chemically pure SiO
2
, Al
2
O
3
,H
3
BO
3
,
Na
2
CO
3
, ZrO
2
and Sb
2
O
3
. ZrO
2
and Sb
2
O
3
were added in order to im-
prove glass stability in molten salts and to avoid microbubbles, respec-
tively. The melt was quenched by pouring out into a brass mould, and
the resultant glass was annealed for 2 h at glass transition temperature
T
g
= 555 °C which was determined using viscosity measurements. Na-
glass samples were exposed to a melt of dilute AgNO
3
(95 mol% NaNO
3
and 5 mol% AgNO
3
) at 340 °C for 180 min. This procedure was expected
[4] to result in almost full replacement of Na
+
ions in the subsurface
Journal of Non-Crystalline Solids xxx (2013) xxx–xxx
⁎ Corresponding author.
E-mail address: estavrou@eie.gr (E. Stavrou).
NOC-16800; No of Pages 5
0022-3093/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jnoncrysol.2013.12.017
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids
journal homepage: www.elsevier.com/ locate/ jnoncrysol
Please cite this article as: E. Stavrou, et al., Vibrational study of thermally ion-exchanged sodium aluminoborosilicate glasses, J. Non-Cryst. Solids
(2013), http://dx.doi.org/10.1016/j.jnoncrysol.2013.12.017