Synthesis and Properties of Vanadium Substituted Bismuth Tungstates with Fluorite-like Structure


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Kaimieva O. S., Sabirova I. E., Buyanova E. S., Petrova S. A.
Chimica Techno Acta. 2019. Vol. 6, No. 2. P. 46–50.

ISSN 2409–5613

O. S. Kaimievaa, I. E. Sabirovaa,  
E. S. Buyanovaa, S. A. Petrovab

a Institute of Natural Sciences and Mathematics, Ural Federal University,  
19 Mira st., Ekaterinburg 620002, Russia

b Institute of Metallurgy, Ural Branch of Academy of Sciences,  
101 Amundsena st., Ekaterinburg 620026, Russia

e-mail: kaimi-olga@mail.ru

Synthesis and Properties of Vanadium Substituted 
Bismuth Tungstates with Fluorite‑like Structure

The samples of vanadium substituted bismuth tungstates with a cubic struc-
ture were obtained by solid state method. The unit cell volume of the compounds 
slightly contracts with increasing tungsten content and in case of vanadium dop-
ing. Thermal expansion coefficient of bismuth tungstate is equal to 13·10–6 °C–1. 
The electrical conductivity was investigated using ac impedance spectroscopy. 
The results showed that the substitution of tungsten with vanadium ions increased 
electrical conductivity values by one order of magnitude.

Keywords: bismuth tungstate; fluorite-like structure; oxide-ion conductivity; solid electrolyte.

Received: 05.07.2019. Accepted: 23.07.2019. Published: 05.08.2019.

© Kaimieva O. S., Sabirova I. E., Buyanova E. S., Petrova S. A., 2019

Introduction
δ-Bi2O3 has the  highest value 

of electrical conductivity (1–1.5 Ohm–1cm–1) 
among all known complex oxide electrolyte 
materials for electrochemical devices [1, 2]. 
The main disadvantage of this phase is that 
it is stable only within a limited tempera-
ture range (730–825 °C). A large number 
of  studies are connected with searching 
for the best way of its stabilization at room 
temperature preserving its characteristics. 
For this purpose, substitution with vari-
ous suitable ions (Nb5+, Mo6+, Ta5+, Ti4+, 
W6+ etc.) is usually used [1–4]. It is found 
for Bi2O3-WO3 system that the introduc-
tion of tungsten oxide (more than 9 wt.%) 
is a necessary condition for stabilization 
of δ-phase Bi2O3 [5]. Otherwise, β-Bi2O3 
appears. On the  other hand, a  homoge-
neity area of cubic structure on the phase 

diagram exists between compounds with 
compositions 2:1 and 5:1. Bi6WO12 has 
fluorite-like structure as well. This com-
pound melts congruently at 1040 °C and 
has reversible phase transition at 900 °C. 
So, as  it was shown by  Wind [6, 7], bis-
muth tungstates with a fluorite-like struc-
ture are promising as compounds which 
have values of  electrical conductivity 
comparable with those of yttria-stabilized 
zirconia. Three more stable cubic phases, 
Bi22W5O48, Bi22W4.5O47.25, and Bi23W4O46.5, 
were obtained at  room temperature via 
quenching [6, 7]. In  case of  low cooling 
rate, a phase transition from cubic to te-
tragonal structure occurs at 700 °C. Un-
til now, many authors have agreed that 
the phase diagram of Bi2O3–WO3 system 
is  complex enough and requires a  de-



47

tailed study. Takahashi and Iwahara [8] 
have done research on ionic properties 
of (Bi2O3)1–x(WO3) x (x  = 0.05–0.5) and 
found extremely high oxide-ion conduc-
tivity for the  fcc structure over the  wide 
range of temperatures, up to at least 850 °C. 
The  conductivities in (Bi2O3)0.78(WO3)0.22 
are 0.01 and 0.15 Ohm–1cm–1 at 500 and 
880 °C, respectively. The oxide ion transfer 

number is close to 1 down to oxygen partial 
pressure p(O2) = 10

–15 atm [8].
There data on substituted bismuth tung-

states Bi22W5O48, Bi22W4.5O47.25, Bi23W4O46.5 
have not been found in literature. There-
fore, the aim of this work is to obtain and 
study of the structure and physicochemi-
cal properties of bismuth tungstates doped 
with vanadium ions.

Experimental
S a m p l e s  B i 2 2 W 5 – x V x O 4 8 – δ , 

Bi22W4.5–xVxO47.25–δ, Bi23W4–xVxO46.5–δ (x = 0.0; 
0.1) were prepared by solid-state method. 
Metal oxides Bi2O3 (99.99 %), WO3 (99.9 %), 
V2O5 (99.9 %) were taken as  precursors. 
The multi-step synthesis was carried out 
in  the  temperature range 400–1000  °C. 
Annealing time was 8 hour at each stage. 
The synthesis into pressed bars was per-
formed after annealing of powder samples 
at 700 °C. The samples were quenched after 
the last stage of the synthesis. The phase 
composition of  the  powders was deter-
mined by means of X-ray powder diffrac-
tion (DRON3 diffractometer, Russia, Cu Kα 
radiation). The phase purities of the com-
pounds were confirmed by  comparing 
their XRD patterns with those in the PDF2 
database. The density of sintered bars was 
estimated by Archimedes method.

Dilatometric measurements were car-
ried out on rectangular bars with the length 
of 23 mm using a DIL 402 C Netzsch dilato-
meter in the temperature range 20–900 °C 
with a heating rate of 2 °C/min. The electri-
cal conductivity values were found by ac 
impedance spectroscopy method (imped-
ance meter Z-3000 “Elins”, Russia) using 
two-probe cell. The  measurements were 
performed in the temperature range 850–
200 °C and frequency span 3 MHz —  1 Hz 
at the cooling mode. Obtained impedance 
spectra were treated with “ZView” software 
and equivalent circuits were fitted to them. 
Using these data, the temperature depend-
ences of  electrical conductivity (σ) were 
plotted in Arrhenius coordinates –lgσ —  
1000/T.

Results and discussion
According to results of X-ray diffrac-

tion analysis, all obtained compounds were 
single-phase with cubic structure (space 
group Fm3m). X-ray diffraction patterns 
of the Bi22W5–xVxO48–δ, Bi22W4.5–xVxO47.25–δ, 
Bi23W4–xVxO46.5–δ (x  = 0.0–0.1) are given 
in Fig. 1. The unit cell parameters are listed 
in Table 1. As the radius of vanadium ions 
is smaller than that of tungsten ions (r(Bi3+) 
= 0.60 Å; r(W6+) = 0.60 Å; r(V5+) = 0.54 Å 
[9]), one can observe slight contraction 

of unit cell volume of the substituted com-
pounds. The same tendency is found for 
the samples with increasing tungsten con-
tent and is reported in [6, 7]. On the whole, 
all experimental data which are obtained 
in the present work for matrix compounds 
are in a good agreement with previous re-
sults [6, 7].

For the further dilatometric and elec-
trical conductivity measurements, the bis-
muth tungstates were pressed and sintered 



48

into bars. Volume porosity of the ceramics 
obtained at 850 °C was estimated by Ar-
chimedes method. The average value was 
10 %. For the Bi23W4O46.5 sample, a peak 
was observed on the cooling curve of ther-
mal expansion coefficient (TEC) near 

430 °C (Fig. 2). This peak can be related 
to  the  presence of  the  phase transition 
from cubic to tetragonal structure [6, 7]. 
TEC value of  the  Bi23W4O46.5 equals to 
13·10–6  °C–1 and is  close to  that for lan-
thanum manganite cathode materials. 
As  the  temperature of  the  measurement 
(900 °C) was higher than that for sinter-
ing of the bar (850 °C), there is hysteresis 
between the  heating and cooling curves 
on the temperature dependence of linear 
thermal expansion (Fig. 2).

The electrical conductivity was investi-
gated by ac impedance spectroscopy using 
two-probe method. Introducing of vanadi-
um ions into the structure of bismuth tung-
state leads to significant reduction of sam-
ples’ resistance. The equivalent circuits were 
matched to impedance spectra to describe 
processes taking place in the samples dur-
ing the measurements (Fig. 3). The circuits 
can be divided into two types. For the high-
temperature range, general resistivity 
of the samples can be defined (R1) (Fig. 3). 
Other elements of this circuit (R2+CPE1, 
R3+CPE2) are related to electrode processes 
because the value of their capacity is equal to 
4×10–4 F. But at low temperatures it is possi-
ble to estimate volume and grain boundary 
contribution to the electrical conductivity 
value (Fig. 3). For example, for the composi-
tion Bi22W4.9V0.1O48–δ, the volume resistance 
(R1) equals to 14 kOhm at capacity (CPE1) 

Table 1
The unit cell parameters of the bismuth tungstates

Composition А ± 0.001, Å V ± 0.03, Å3

Bi23W4O46.5 5.569 172.73

Bi23W3.9V0.1O46.5–δ 5.569 172.60

Bi22W4.5O47.25 5.562 172.05

Bi22W4.4V0.1O47.25–δ 5.558 171.72

Bi22W5O48 5.549 170.85

Bi22W4.9V0.1O48–δ 5.546 170.60

Fig. 2. Temperature dependence of linear 
thermal expansion and TEC for the sample 

Bi23W4O46.5

Fig. 1. X-ray diffraction pattern  
of the bismuth tungstates



49

3×10–11  F, the  grain boundary resistance 
(R2) to 185 kOhm at 2×10–5 F (CPE2). Tem-
perature dependences of the general electri-
cal conductivity of the bismuth tungstates 
were plotted using the data of the imped-
ance spectra (Fig. 4). The results show that 
the substitution of tungsten with vanadium 
ions increases electrical conductivity values 
by one order of magnitude. The activation 
energy values for all bismuth tungstates are 
between 0.88–1.02 eV (Table 2), indicating 
that the samples have ionic type of con-
ductivity. According to our measurements, 
Bi23W3.9V0.1O46.5–δ possesses the  highest 
conductivity of all oxides studied (σ850 = 
0.13 Ohm–1cm–1).

Conclusions
To sum up, the solid solutions based on 

bismuth tungstates with fluorite-like struc-
ture were obtained by solid state method. 

The  unit cell volume of  the  compounds 
slightly contracts with increasing tungsten 
content and in case of vanadium doping. 

Fig. 4. Temperature dependences  
of the general electrical conductivity  

of the bismuth tungstates

Fig. 3. Impedance spectra of the Bi22W4.9V0.1O48–δ at 800 °C and 400 °C

Table 2
Electrical conductivity (σ) and activation energy (Ea) values of the bismuth tungstates

Composition Еa, eV σ750, Ohm
–1cm–1 σ500, Ohm

–1cm–1

Bi23W4O46.5 0.99 7.74·10
–2 1.30·10–2

Bi23W3.9V0.1O46.5–δ 0.88 2.85·10
–1 6.69·10–2

Bi22W4.5O47.25 1.00 5.92·10
–3 7.66·10–5

Bi22W4.4V0.1O47.25–δ 1.02 7.84·10
–3 1.30·10–4

Bi22W5O48 0.92 1.01·10
–1 1.91·10–2

Bi22W4.9V0.1O48–δ 0.95 1.82·10
–1 3.50·10–2



50

TEC of the Bi23W4O46.5 sample is equal to 
13·10–6 °C–1. A small peak on the cooling 
curve was observed at 430 °C, which can 
be contributed to the phase transition from 
cubic to tetragonal phase. The introduction 

of vanadium ions into bismuth tungstate 
structure has a positive effect on the electri-
cal conductivity (the Bi23W4.9V0.1O46.5–δ has 
the highest value σ850 = 0.13 Ohm

–1cm–1).

Acknowledgements
This work was performed within the State Assignment of the Ministry of Education 

and Science of the Russian Federation no. 4.2288.2017/4.6. Powder X-ray diffraction stud-
ies were performed on the equipment of the Ural-M Shared Facility Center of the Institute 
of Metallurgy of the Ural Branch of the Russian Academy of Sciences (IMET UB RAS).

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