Journal of Materials Processing Technology 143–144 (2003) 420–424
DC conductivity of GeSeAg glasses at room temperature
M. Mirandou, M. Fontana
∗
, B. Arcondo
Depto. de F´ ısica, Facultad de Ingenier´ ıa, UBA, Paseo Colón 850 (1063), Buenos Aires, Argentina
Abstract
Ionic conducting glasses are used as electrolytes in electrochemical applications (microbatteries, sensors, etc.). An interesting superionic
amorphous alloy is Ge–Se–Ag where the conducting species is the Ag
+
ion. This system is a good glass forming material which does not
need high cooling velocities in a wide concentration range in the Se-rich corner. A maximum Ag content of 30 at.% could be introduced
into a Se-rich sample with the composition GeSe
3
while still retaining the vitreous character. X-ray scattering curves are characterised
by a first scattering peak (FSP) located at q ≈ 1Å
-1
which corresponds to an intermediate range order [J. Non-Cryst. Solids 273
(2000) 30]. The fundamental structural unit of the glass is the GeSe
4/2
tetrahedra. In this work, we study the electric behaviour of the
amorphous GeSeAg system. Glasses of the (GeSe
3
)
100-x
Ag
x
system were prepared in the composition range from x = 0 to 25 at.%.
The electrical characterisation was performed using AC voltages with frequencies ranging from 100 Hz to 100 KHz. The conductivity
(σ ≈ 10
-4
-1
cm
-1
for x = 25 at room temperature) shows a monotonous decrease with decreasing Ag concentration. We discuss the
relation between the glass structure and their electrical properties.
© 2003 Elsevier Science B.V. All rights reserved.
Keywords: DC conductivity; Ionic conductors; Chalcogenides; GeSeAg
1. Introduction
The high ionic conductivity of superionic conducting
glasses makes these materials very interesting for applica-
tions in microbatteries and microsensors [1]. Glasses on the
selenium-rich side of the GeSe
2
–Ag
2
Se tie line are fast ion
conductors with silver as the mobile cation.
The GeSeAg glass is likely to share many structure and
transport characteristic with the (network former)–(network
modifier) family of glasses. In this glass, Ge is termed the
network forming cation, Ag the mobile cation and Se the
anion [2]. The structure of this glass has been investigated
[2–4] and a short range order due to GeSe
4/2
tetrahedra was
reported. However, the correlation of the Ag is motive of
controversy. The glass homogeneity generates dispute too.
Some works propose that (Ge
0.25
Se
0.75
)
0.75
Ag
0.25
glasses
are homogeneous bulk glasses [2,3]. However, in a recent
work, ternary (Ge
z
Se
1-z
)
1-y
Ag
y
bulk glasses in the Se-rich
region (z< 1/3) are shown to be intrinsically phase sepa-
rated into an Ag
2
Se-rich glass and a residual Ge
t
Se
1-t
(t>
z at y = 0) with Ag acting as a network modifier [5]. They
observed bimodal glass transition temperatures. In contrast,
Ge-rich glasses (z> 5/2) were reported as homogeneous,
∗
Corresponding author.
E-mail address: mfontan@fi.uba.ar (M. Fontana).
wherein Ag acts as a network former, replacing available Ge
sites of the backbone to be threefold coordinated to Se.
The crystallisation processes of AgGeSe glasses have
been studied. The glass temperature, the crystallisa-
tion temperature and crystallisation activation energy of
(GeSe
3
)
100-x
Ag
x
glasses are reported [6]. Recently, elec-
trical properties of (Ge
25
Se
75
)
100-x
Ag
x
glasses were in-
vestigated by impedance spectra. As the concentration of
silver is increased the total electrical conductivity steeply
increases from 10
-13
to 10
-5
-1
cm
-1
at about x
∗
= 10
[7]. They supposed a percolation transition is happening
at x
∗
.
Despite the considerable efforts devoted to understanding
ion motion in glasses, several aspects of the problem still
remain obscure [1]. For example, the strong dependency of
conductivity upon the content of modifier is still a matter for
controversy [1]. In the present work, we report the results
of conductivity measurements of (GeSe
3
)
100-x
Ag
x
glasses.
The aim of this study is to investigate the dependence Ag
+
ion conductivity with Ag content and its connection with the
amorphous structure.
2. Experimental
(GeSe
3
)
100-x
Ag
x
samples with x = 0, 10, 15, 20 and
25 at.%, were prepared with 99.99% purity elements. In all
0924-0136/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0924-0136(03)00437-0