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Ceramics International
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Enhancing the electrical conductivity of vanadate glass system (Fe
2
O
3
,B
2
O
3
,
V
2
O
5
) via doping with sodium or strontium cations
Fatma H. Margha
a,*
, Gehan T. El-Bassyouni
b
, Gamal M. Turky
c
a
Glass Research Department, National Research Centre, 33 El Bohouth St. (Former El Tahrir St.), Dokki, Giza, P.O. 12622, Egypt
b
Refractories, Ceramics and Building Materials Department, National Research Centre, 33 El Bohouth St. (Former El Tahrir St.), Dokki, Giza, P.O. 12622, Egypt
c
Department of Microwave Physics and Dielectrics, National Research Centre, 33 El Bohouth St. (Former El Tahrir St.), Dokki, Giza, P.O. 12622, Egypt
ARTICLE INFO
Keywords:
Glass ceramic
Strontium vanadate
Iron vanadate
Electrical conductivity
Dielectrics
ABSTRACT
Novel glass-ceramics of the nominal molar compositions 20Fe
2
O
3
·20B
2
O
3
·(60-x)V
2
O
5
· (xNa
2
O or xSrO) (where
x = 0 or 10) were prepared by traditional melt technique. Differential thermal analysis (DTA) was implemented
to study the thermal behavior of the prepared glasses. Vanadium pentoxide (V
2
O
5
), iron vanadate (FeVO
4
),
sodium vanadate (Na
3
VO
4
) and strontium vanadate (with different formulae) were crystallized and identified by
X-ray diffraction (XRD) analysis under certain conditions of heat-treatment. Further characterization of glass and
glass ceramics samples were performed using scanning electron microscope (SEM), density, electrical and di-
electric measurements. In conclusion, our study elucidated that the substitution of vanadium by Na
+
and Sr
2+
ions enhanced the conductivity at 180 °C from 5.11 × 10
-4
for unmodified glass to 2.93 × 10
-3
and
1.03 × 10
-2
S cm
-1
for Na- and Sr-modified glasses.
1. Introduction
Electrically conducting and semiconducting transition metal oxide
glasses have attracted the attention recently due to their possible ap-
plications in various technological fields [1,2]. Among such glasses,
vanadate glasses are very promising materials In this type of glass, V
2
O
5
participates in the glass network with VO
5
pyramidal structural units
containing V
4+
and V
5+
ions [3,4]. Thanks to the small polaron hop-
ping of 3 d
1
unpaired electron between V
4+
and V
5+
ions existing in the
structure of vanadate glasses [5,6] that allow vanadate glasses to have
electrical conductivity as high as 10
-3
- 10
-5
Sm
-1
[3,7]. Accordingly,
vanadate glasses are utilized in memory and switching devices and
many other applications [8,9].
On the other hand, borate glasses, are also important for various
practical applications owing to their unique structure, low melting
temperature, high transparency, high dielectric constant, and high
thermal stability [10]. Borate glass network usually consists of two
groups of bands: (1) trigonal boroxol rings (BO
3
) and (2) tetrahedral 4-
fold coordinated boron (BO
4
); the addition of a modifier brings about
the formation of a new 3-fold coordinated boron along with formation
of a non-bridging oxygen (NBO) [6,10]. Insertion of transition metal
ions, such as vanadium or iron, to the borate glasses converts it from
insulating glasses into semiconducting glasses [10,11]. Consequently,
Fe
2
O
3
-B
2
O
3
-V
2
O
5
is expected to have promising semiconducting
properties. Kundu et al. (2008) [11] investigated the structural and
physical properties of xFe
2
O
3
-(40-x) B
2
O
3
-60V
2
O
5
(0 ≤ x ≤ 20) glass
system. They obtained electrical conductivity of up to
4.194 × 10-2Sm
-1
when x = 20. However, their study was limited
to the glass form of this system.
To the best of our knowledge, no previous studies were performed
on this specific composition of glass-ceramic. Therefore, the present
study aims, for the first time, to study the electrical conductivity of the
system Fe
2
O
3
-B
2
O
3
-V
2
O
5
upon applying a proper heat treatment to
allow crystallization of this system. Moreover, alkali metals (Na
2
O) or
alkaline earth (SrO) oxides were introduced to this system on the ex-
pense of V
2
O
5
as different modifiers for further enhancement of elec-
trical conductivity of this system. The electrical properties of the pre-
pared materials (i.e., conductivity and dielectric constant) were studied
extensively using the broadband dielectric spectroscopy (BDS). It is the
more suitable technique for probing molecular dynamics as well as the
charge carriers’ transportation in many advanced materials according
to its wide range of frequency and temperature [12]. The complex di-
electrics function = ′ − ′
∗ ′
ε ωT ε ωT ε ωT ( , ) ( , ) ( , ), where ′ ε is the per-
mittivity and ′
′
ε is the dielectric loss, could be obtained in the frequency
range 10
-1
-10
7
Hz. It is equivalent with the complex conductivity
function = ′ + ′
∗ ′
σ ωT σ ωT σ ωT ( , ) ( , ) ( , ) since,
∗
σ
=
∗
ωT iωε ε ωT ( , ) ( , )
o
, implying that ′= ′
′
σ ε ωε
o
and ′= ′
′
σ ε ωε
o
(ε
o
being
the vacuum permittivity).
https://doi.org/10.1016/j.ceramint.2019.03.064
Received 3 February 2019; Received in revised form 5 March 2019; Accepted 10 March 2019
*
Corresponding author.
E-mail address: fatmamargha@yahoo.com (F.H. Margha).
Ceramics International 45 (2019) 11838–11843
Available online 12 March 2019
0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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