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Structure of new anionic conductors Bi4V2(1−xM2xO11−3x; M = Cu, Ni
Physica B 180 & 181 (1992) North-Holland
PHYSICA 1
621-623
Structure of new anionic conductors M = Cu,Ni
Bi,V,, 1 _,,M,,O
1 1 -3X ;
M. Anne”, M. Bacmanna, E. Pernota, F. Abrahamb, G. Mairesseb and P. Strobel” “Laboratoire de Cristallographie, CNRS, AssociP ci I’Universiti .I. Fourier, B. P. 166, 38042Grenoble Cedex 09, France hLaboratoire de Cristallochimie et Physicochimie du Solide U. A. 4.52, CNRS, ENS de Chimie de Lille, B. P. 108, 59652 Villeneuve d’ Ascq Cedex, France
From neutron diffraction data, crystal structure determinations of various B&V,, ,_,,M,,O,, _3xcompounds were carried out using Rietveld type full profile refinement procedures. All these compounds belong to the y-phase of Bi,VzO,, and the substitution rates deduced from the refined parameters are strongly related to oxygen vacancies of the structure.
1. Introduction
The new compound Bi_,V,O,, exhibits three structural phases in the temperature range 300-1160 K [l]. The structures of the different phases are related to that of the Aurivillius phases B&MO, (M = MO, W). This structure-type consists of alternate layers of M-O corner-sharing octahedra (perovskite-like) and B&O, sheets, the perovskite layers being oxygen-deficient (BiZVG,,&,) (fig. I). Disorder, at least in the high temperature phase (-y-form), leads to high anionic conductivity. At lower temperatures (o and p-forms) the structure becomes ordered, the unit cells larger and the conductivity significantly lower. Partial substitutions of vanadium by other transition metals such as Cu, can stabilize the Bi
high temperature y-phase at room temperature, thus enhancing its ionic conductivity [2]. In order to obtain accurate information concerning the stability range of the y-phase and the anionic conductivity dependence as a function of the rate of substitution, the crystal structure of various substituted compounds was determined. 2. Experimental Polycrystalline substituted samples of various compositions were prepared by heating the appropriate oxides Bi,O,, V,O, and CuO (or NiO) to about 870 K, regrinding and calcination at 1120 K for 20 hours in gold crucibles in air. Neutron experiments were performed at the Institut Laue-Langevin (ILL), Grenoble. The powder diffraction patterns were recorded on the D20-diffractometer at a wavelength A = 2.412 A. The structure determinations were carried out using Rietveld-type full profile refinement methods [3]. 3. Results
Fig. 1. Schematic y-Bi,V,O,, 0921-4526/92/$05.00
representation
0
of the
1992 - Elsevier
ideal
Science
structure
Publishers
of
For the Ni-doped Bi4V20,,, three different compositions corresponding to x = 0.10, 0.15 and 0.20 were studied while for the Cu-doped compound only the x = 0.10 composition was investigated. Single crystal X-ray diffraction of this latter phase showed that the high temperature tetragonal y-form was stabilized by such a Cu-substitution [2]. Neutron diffraction pattern preliminary studies confirm the tetragonal y-phase for all these substituted compounds. Profile analysis refinements of the structures were achieved assuming 14/mmm symmetry. The lattice parameters obtained are given in table 1. The increase in the quantity of Ni atoms in the BiNiVOX compounds leads to an increase of the tetragonal cell parameters. The structural parameters including
B.V. All rights
reserved
M. Anne et al. I Structure of new anionic conductors
622
4. Discussion
atomic positions, overall temperature factor and site occupancies are given in table 2 for the BiNiVOXlO compound. Figure 2 shows the agreement between the observed and calculated profiles. For the other Ni-atom compositions and the Cudoped compound the results confirm the atomic positions given in table 2 and all the agreement factors R,, are about 8%. Table 1 Lattice parameters
a=b c
Table 2 Results of the total profile R Bragg= 12.0, N: occupation
For the Ni-doped compounds the refined compositions are in good agreement with those predicted while a great discrepancy is observed between the two values in the case of the Cu-doped compound (table 3). The existence of reflections corresponding to impurities in the neutron diffraction pattern could ex-
of the BiMVOX-phases
(in A).
BiNiVOXlO
BiNiVOX15
BiNiVOX20
BiCuVOXlO
3.92594 (16) 15.4485 (11)
3.93102 (17) 15.4709 (11)
3.93675 (17) 15.4897 (11)
3.92200 (18) 15.4467 (12)
refinement number.
of the structure
of BiNiVOXlO.
B,,,,,,,
Atom
Position
X
Y
Bi Ni V 01 02 03
16m 8h 8h 4d 16m 8g
0.0168 (42) 0.6334 (90) 0.6334 (90) 0 0.1082(19) 0
0.0168 0.6334 0.6334 112 0.1082 112
J II
20
40
I
I II
I
60
I
l
11111
I
80
TWO THETA
=1.8
(0.1)
(42) (90) (90) (19)
I
ll/ll
100
l
I?,=
1.43,
R,=6.10,
R,,=7.93,
z
N
0.1685 (1) 0 0 l/4 0.4038 (4) 0.0343 (5)
2 0.1264 (80) 0.8736 (80) 2 1.90 (3) 1.296 (21)
III1
120
III
I
/l
140
(deg)
Fig. 2. Observed and calculated neutron powder diffraction pattern for BiNiVOXlO. reflections of the two phases NiO and BiNiVOXlO (up and down respectively).
The vertical
bars mark
the positions
of the
M. Anne et al. I Structure
Table 3 Comparison between the chemical composition (x,,) and the refined one (x,,).
X cc
x,,
Ni
Ni
Ni
CU
0.10 0.126 (8)
0.15 0.166 (8)
0.20 0.198 (8)
0.10 0.188 (12)
plain a change in the chemical latter compound. The above atom distribution seem entirely satisfactory since
composition
of this
(table 2) does not the overall Debye-
Waler factors (==2 A’) and the reliability factors (R, = 1.5%; R,,~8%) are still relatively high. In fact this model corresponds to a mean structure with partial occupancies on both metal and some oxygen sites. Introduction in the refinement of the Bi atoms positions reported previously [2] led to a poor agreement but a statistical Bi atoms distribution on an unique crystallographic site (16 m) permitted a good description of the structure. The oxygen atoms are distributed Table 4 Refined and calculated oxygen-vacancies
BiNiVOXlO BiNiVOX15 BiNiVOX20 BiCuVOXlO
of new anionic conductors
623
over the three sites described in [2] and the partial occupancies of the 02 and 03 sites were refined. Only the 01 sites belonging to B&O:+ layers, remain fully occupied. The vacancies on the 02 and 03 sites (respectively about 10 and 35%) are certainly responsible for the ionic conductivity of the compounds. The composition of the substituted compounds can be described by the formula: B&Ot+(V, Cu or Ni)O,_,O, where 0 is an oxygen vacancy. Table 4 shows the refined values of t and the related calculated values with the assumption of V5’ ions. In fact the amount of vacancies increases with the rate of Ni*‘. The discrepancies between the refined and calculated values could be explained by the existence of mixed valences for the vanadium atoms (mean value about +4.7) or by the presence of metal vacancies on the 3d-metal site (about 5% for the Nicompounds). The present results constitute a preliminary determination of the BiMVOX structure. Single crystal data are needed in order to improve our model. References
concentrations
(t).
refined
calculated
0.80 0.88 0.91 0.84
0.69 0.75 0.80 0.78
[l] F. Abraham, M.F. Debreuille-Gresse, G. Mairesse and G. Nowogrocki, Solid State Ionics 28-30 (1988) 529. [2] F. Abraham, J.C. Boivin, G. Mairesse and G. Nowogrocki, Solid State Ionics 40-41 (1990) 934. [3] J. Rodriguez-Carvajal, Satellite Meeting on Powder Diffraction of the 15th Congress of the International Union of Crystallography, Toulouse (1990) 127.
PHYSICA 1
621-623
Structure of new anionic conductors M = Cu,Ni
Bi,V,, 1 _,,M,,O
1 1 -3X ;
M. Anne”, M. Bacmanna, E. Pernota, F. Abrahamb, G. Mairesseb and P. Strobel” “Laboratoire de Cristallographie, CNRS, AssociP ci I’Universiti .I. Fourier, B. P. 166, 38042Grenoble Cedex 09, France hLaboratoire de Cristallochimie et Physicochimie du Solide U. A. 4.52, CNRS, ENS de Chimie de Lille, B. P. 108, 59652 Villeneuve d’ Ascq Cedex, France
From neutron diffraction data, crystal structure determinations of various B&V,, ,_,,M,,O,, _3xcompounds were carried out using Rietveld type full profile refinement procedures. All these compounds belong to the y-phase of Bi,VzO,, and the substitution rates deduced from the refined parameters are strongly related to oxygen vacancies of the structure.
1. Introduction
The new compound Bi_,V,O,, exhibits three structural phases in the temperature range 300-1160 K [l]. The structures of the different phases are related to that of the Aurivillius phases B&MO, (M = MO, W). This structure-type consists of alternate layers of M-O corner-sharing octahedra (perovskite-like) and B&O, sheets, the perovskite layers being oxygen-deficient (BiZVG,,&,) (fig. I). Disorder, at least in the high temperature phase (-y-form), leads to high anionic conductivity. At lower temperatures (o and p-forms) the structure becomes ordered, the unit cells larger and the conductivity significantly lower. Partial substitutions of vanadium by other transition metals such as Cu, can stabilize the Bi
high temperature y-phase at room temperature, thus enhancing its ionic conductivity [2]. In order to obtain accurate information concerning the stability range of the y-phase and the anionic conductivity dependence as a function of the rate of substitution, the crystal structure of various substituted compounds was determined. 2. Experimental Polycrystalline substituted samples of various compositions were prepared by heating the appropriate oxides Bi,O,, V,O, and CuO (or NiO) to about 870 K, regrinding and calcination at 1120 K for 20 hours in gold crucibles in air. Neutron experiments were performed at the Institut Laue-Langevin (ILL), Grenoble. The powder diffraction patterns were recorded on the D20-diffractometer at a wavelength A = 2.412 A. The structure determinations were carried out using Rietveld-type full profile refinement methods [3]. 3. Results
Fig. 1. Schematic y-Bi,V,O,, 0921-4526/92/$05.00
representation
0
of the
1992 - Elsevier
ideal
Science
structure
Publishers
of
For the Ni-doped Bi4V20,,, three different compositions corresponding to x = 0.10, 0.15 and 0.20 were studied while for the Cu-doped compound only the x = 0.10 composition was investigated. Single crystal X-ray diffraction of this latter phase showed that the high temperature tetragonal y-form was stabilized by such a Cu-substitution [2]. Neutron diffraction pattern preliminary studies confirm the tetragonal y-phase for all these substituted compounds. Profile analysis refinements of the structures were achieved assuming 14/mmm symmetry. The lattice parameters obtained are given in table 1. The increase in the quantity of Ni atoms in the BiNiVOX compounds leads to an increase of the tetragonal cell parameters. The structural parameters including
B.V. All rights
reserved
M. Anne et al. I Structure of new anionic conductors
622
4. Discussion
atomic positions, overall temperature factor and site occupancies are given in table 2 for the BiNiVOXlO compound. Figure 2 shows the agreement between the observed and calculated profiles. For the other Ni-atom compositions and the Cudoped compound the results confirm the atomic positions given in table 2 and all the agreement factors R,, are about 8%. Table 1 Lattice parameters
a=b c
Table 2 Results of the total profile R Bragg= 12.0, N: occupation
For the Ni-doped compounds the refined compositions are in good agreement with those predicted while a great discrepancy is observed between the two values in the case of the Cu-doped compound (table 3). The existence of reflections corresponding to impurities in the neutron diffraction pattern could ex-
of the BiMVOX-phases
(in A).
BiNiVOXlO
BiNiVOX15
BiNiVOX20
BiCuVOXlO
3.92594 (16) 15.4485 (11)
3.93102 (17) 15.4709 (11)
3.93675 (17) 15.4897 (11)
3.92200 (18) 15.4467 (12)
refinement number.
of the structure
of BiNiVOXlO.
B,,,,,,,
Atom
Position
X
Y
Bi Ni V 01 02 03
16m 8h 8h 4d 16m 8g
0.0168 (42) 0.6334 (90) 0.6334 (90) 0 0.1082(19) 0
0.0168 0.6334 0.6334 112 0.1082 112
J II
20
40
I
I II
I
60
I
l
11111
I
80
TWO THETA
=1.8
(0.1)
(42) (90) (90) (19)
I
ll/ll
100
l
I?,=
1.43,
R,=6.10,
R,,=7.93,
z
N
0.1685 (1) 0 0 l/4 0.4038 (4) 0.0343 (5)
2 0.1264 (80) 0.8736 (80) 2 1.90 (3) 1.296 (21)
III1
120
III
I
/l
140
(deg)
Fig. 2. Observed and calculated neutron powder diffraction pattern for BiNiVOXlO. reflections of the two phases NiO and BiNiVOXlO (up and down respectively).
The vertical
bars mark
the positions
of the
M. Anne et al. I Structure
Table 3 Comparison between the chemical composition (x,,) and the refined one (x,,).
X cc
x,,
Ni
Ni
Ni
CU
0.10 0.126 (8)
0.15 0.166 (8)
0.20 0.198 (8)
0.10 0.188 (12)
plain a change in the chemical latter compound. The above atom distribution seem entirely satisfactory since
composition
of this
(table 2) does not the overall Debye-
Waler factors (==2 A’) and the reliability factors (R, = 1.5%; R,,~8%) are still relatively high. In fact this model corresponds to a mean structure with partial occupancies on both metal and some oxygen sites. Introduction in the refinement of the Bi atoms positions reported previously [2] led to a poor agreement but a statistical Bi atoms distribution on an unique crystallographic site (16 m) permitted a good description of the structure. The oxygen atoms are distributed Table 4 Refined and calculated oxygen-vacancies
BiNiVOXlO BiNiVOX15 BiNiVOX20 BiCuVOXlO
of new anionic conductors
623
over the three sites described in [2] and the partial occupancies of the 02 and 03 sites were refined. Only the 01 sites belonging to B&O:+ layers, remain fully occupied. The vacancies on the 02 and 03 sites (respectively about 10 and 35%) are certainly responsible for the ionic conductivity of the compounds. The composition of the substituted compounds can be described by the formula: B&Ot+(V, Cu or Ni)O,_,O, where 0 is an oxygen vacancy. Table 4 shows the refined values of t and the related calculated values with the assumption of V5’ ions. In fact the amount of vacancies increases with the rate of Ni*‘. The discrepancies between the refined and calculated values could be explained by the existence of mixed valences for the vanadium atoms (mean value about +4.7) or by the presence of metal vacancies on the 3d-metal site (about 5% for the Nicompounds). The present results constitute a preliminary determination of the BiMVOX structure. Single crystal data are needed in order to improve our model. References
concentrations
(t).
refined
calculated
0.80 0.88 0.91 0.84
0.69 0.75 0.80 0.78
[l] F. Abraham, M.F. Debreuille-Gresse, G. Mairesse and G. Nowogrocki, Solid State Ionics 28-30 (1988) 529. [2] F. Abraham, J.C. Boivin, G. Mairesse and G. Nowogrocki, Solid State Ionics 40-41 (1990) 934. [3] J. Rodriguez-Carvajal, Satellite Meeting on Powder Diffraction of the 15th Congress of the International Union of Crystallography, Toulouse (1990) 127.