Electrochimica Acta 46 (2001) 2059 – 2068
Electrochromic and structural investigation of InVO
4
and
some other vanadia-based oxide films
B. Orel
a,
*, A. S urca Vuk
a
, U. Opara Kras ˇovec
a
, G. Draz ˇic ˇ
b
a
National Institute of Chemistry, Hajdrihoa 19, SI -1000 Ljubljana, Sloenia
b
Joz ˇef Stefan Institute, Jamoa 39, SI -1000 Ljubljana, Sloenia
Received 21 August 2000; received in revised form 2 November 2000
Abstract
We extended our previous studies of M
3 +
VO
4
orthovanadate (M
3 +
=Ce, Fe) and M
2
3 +
V
4
O
13
(Fe
2
V
4
O
13
) films to
include InVO
4
films because their photopic transmittance T
vis(initial)
is above 0.885. Structural studies (TEM and
XRD) revealed that films prepared from In(NO
3
)
3
·5H
2
O and V-oxoisopropoxide sols annealed at 500°C consist of the
mixed monoclinic (InVO
4
-I) and orthorhombic (InVO
4
-III) phases, while the addition of acetylacetone (acac) to the
sol results in amorphisation. The charge capacity of InVO
4
/acac films is between -30 and -40 mC cm
-2
(single
dipped films) and their electrochemical stability is more than 1000 cycles. In situ UV – visible spectroelectrochemical
measurements show that charging to -35 mC cm
-2
decreases the photopic transmittance from T
vis(initial)
=0.885 to
T
vis(ins)
=0.722, which contrasts the higher optical passiveness of previously investigated CeVO
4
films (T
vis(ins)
=0.90).
The increase in the broad absorption below 600 cm
-1
in IR spectra of charged/discharged InVO
4
films shows that
films irreversibly uptake lithium ions. Charging up to -20 mC cm
-2
does not affect the IR spectra, while charging
up to -40 mC cm
-2
results in the transformation of the film structure, which becomes similar to that of the
amorphous InVO
4
films obtained at 300°C and to certain transition vanadate glasses. IR spectra of other
vanadia-based films, i.e. FeVO
4
, Fe
2
V
4
O
13
, CeVO
4
, and V
2
O
5
films in different state of lithiation are discussed.
© 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Orthovanadates; IR spectroscopy; Electrochromism; Sol – gel; Thin films
www.elsevier.nl/locate/electacta
1. Introduction
Research on electrochromic (EC) windows reveals
that WO
3
is the most appropriate active electrochromic
material [1,2]. During the last decade investigations of
counter-electrodes have been extensive [1 – 10] since the
charge capacity of the existent highly transparent coun-
ter-electrodes is not sufficient to colour the active WO
3
layer in full extent. An ideal counter-electrode film
should combine an ion-storage capacity above -35
mC cm
-2
, a photopic transmittance in the discharged
state (T
vis(ext)
) of at least 0.85 and a small variation in
the photopic transmittance of the film with charging
(T
vis
=0.01–0.05). Accordingly, on the basis of our
previous studies of V
2
O
5
[3,4] and vanadate films
(CeVO
4
[5–7], FeVO
4
[8,9], Fe
2
V
4
O
13
[8,10]) we aim to
elucidate whether or not InVO
4
films fulfil the demands
for counter-electrodes in EC devices.
InVO
4
belongs to a large family of orthovanadate
compounds with a general formula M
3 +
VO
4
(M
3 +
=
In, Fe, Cr, Al, rare earths) [11,12]. The chemistry of
InVO
4
is complex and different crystalline modifica-
tions are known [13 – 15]. The high-temperature or-
thorhombic InVO
4
-III (Cmcm) phase was obtained via
* Corresponding author. Tel.: +386-1-4760-200/276; fax:
+386-1-4259-244.
E-mail address: boris.orel@ki.si (B. Orel).
0013-4686/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII:S0013-4686(01)00406-6