On new mixed conductors of Bi4V2 − xMnxO11 − δ formulation

3ournet M

ALLOYS AHD C.OMPO~D~ ELSEVIER

Journal of Alloys and Compounds 256 (1997) 234-243

On new mixed conductors of Bi4V2_~MnxOll_ ~ formulation M. A l g a ~, M. W a h b i ~, A. A m m a r a, B. T a n o u t i a'*, J . C . G r e n i e r b, J . M , R e a u b ~Laboratoire d,r Chimie du Solide Mineral. Ddpartement de Chimie. Facult~ de~ Sciences Semlalia. Bd. Moulay Abdellah. B.P. S. 15. Univer~it~ Cadi A3Tad. Marrakech. Morocco "h~stit~:t de Chimie de la Mati~re Condens(e de Bordeaux. Av. Dr A. Schweitzer. 33608. Pessuc. France

Received I Malch 1996; revised 18 November 1996; accepted 20 November 1996

Abstract The partial substitution of manganese for vanadium in the perovsklte-like sheets of Bi4V,O** has allowed to stabilize at room temperature the structure of "y-Bi4V_.O~ for 0.15-
Bismruth-vanadiumoxides: Mn substitution; Electrical properties; Ionic conduction

1. Introduction Forty six years ago, Aurivillius prepared and characterized a family of bismuth oxides formulated (Bi.O_.)(A._ ~B.O~,,+ i ) [ ! ]. The structure of these materials is built up from (Bi~O,) '+ layers separated by (A. _, B.O3, , +, )2- perovskite-like slabs, where n = 1, 2, 3 .... 8: n represents the thickness of the perovskite layers in terms of BO6 octahedm. When n = !, the perovskite slab is one octahedron thick; in this way. ~/-Bi2WO6 is constituted perpendicularly to the. c-axis by alternate (Bi.O2) '+ and (WO4)"- layers (Fig,. 1) [1-3]. In 1985, a, new Aurivillius phase containing the V ~÷ cation as B ion was isolated. This material, formulated Bi4V20~, is isostructural with Bi2WO 6, but involves a partially occupied anionic sublattice [4], Since then, a large number of works relative either to Bi4V20~ or to the Bi4V2_~M~OIII_/i phases derived from Bi4V2Oll has allowed to show the interest of such materials as oxygen ion conductors [4-10], Three allotropic forms of Bi4V201 ,, ct-, ~- and ~-, have beea ide~.,'=.fied when temperature increases. The ¢t~->[~ and [3~-->~/transitions take place at 720 and 840 K, respectively, and are reversible [7]. The ct- and [3- forms are of orthorhombic symmet.%, ~qd the "y-form is of tetragonal *Corresponding author. 0925-8388/97/$17.00 ¢'. 1997 Elsevier Science S.A. All rights reserved PII _qNg") ~ .5-8388(96)03106-4

symmetry. The ct- and ~-phases can be considered as partially ordered forms of the "/-high temperature phase. The ~/-phase structure exhibits, perpendicularly to the caxis, ( B i 2 0 2 ) 2+ layers alternating with (VO3.5[2]o.5)2perovskite layers [7,8,1 I]. Unlike Bi2MoO 6 and Bi2WO 6, which may be written (Bi202)2+(BO4) 2- ( B = M o , W) and which are insulators, ~/-Bi4V2Ott is a good oxygen ion conductor, due to the presence of vacancies in the perovskite layers. The ~/-form of Bi4V20~z, stable only above 840 K, can be stabilized at room temperature by partial replacement of V 5+ cations by other metallic ions in the perovskite-like sheets. This is, for instance, the case of the Bi4V2_,M, Oll_ ~ (M=Nb, Ti, AI, Cu, Co,...) phases for x->O.15 [4-12]. We report in this work the results relative to materials where M is Mn.

2. Synthesis and X-ray characterization The different Bi4V2_xMn,O~_ 8 compositions were prepared from mixtures of oxides Bi203, V_,Os and MnO 2 of analytical graae. The mixtnres were ground, introduced into platinum crucibles, heated in air at 860 °C during 48 h and cooled from that t~mperature. Several thermal treatments were necessary to obtain pure microcrystalline powders. The powder samples were characterized by X-ray

235

M. Alga et al. I Journal of Alloys and Compozmds 256 (1997) 234-243

0

o

•

ni

•

N

%-,

Fig. I. The crystal structure of Bi:MO. (M=Mo. W) (after Aurivillius [I]).

xuO. 6 0

l

l

J

.1,,

x=O. 20

_1 x=O. 10

L ; 15

25

35

i

I

45

55 ---

Fig. 2. XRD-patterns of some Bi4V2_,Mn,O,t_. compositions.

20

236

M. Alga et al. / Journal of AIh~ys and C¢mapot,tds 256 (1997) 234-243

diffraction using a DIANO diffractometer with Cu Ket radiation. The X-ray diffraction analysis of the powders obtained after cooling has revealed the existence of three phases formulated Bi.~V,_,Mn,Oan _~: - for 0.0t)-
been carried out. by the pycnometry method, on samples that are finely ground. Fig. 4 gives the composition dependence of the specific mass measured; it may be compared with the specific mass calculated for a substitution mechanism which involves the formation of vacancies in the anionic sublattice of the Bi4V2_xMnxO j~_~ solid solutions. The good agreement between the experimental and calculated values confirms the validity of the substitution mechanism proposed.

3. Magnetic properties Fig. 2 gives the XRD-patterns relative to x=0.10, 0.20 and 0.60. in Bi4~/~_xMn,Oll_ 6, as in the other Bi4V:_,M,Oll_,~ phases derived from Bi.,V20~ [4-10], the et---~/ transformation takes place for x~-0.15. This transition appears consequently as independent of the nature of the M substitutional cation. The variation of the unit cell parameters and volume as a function of x are represented in Fig. 3. A unit cell dilatation is observed when x increases, due mainly to the c parameter iincrease. This result is analogous to that shown for the other Bi4V2_,M,Ota_ ~ phases [8-101. The experimental determination of the specific mass has

Magnetic measurements were carded out using a SQUID magnetometer (Quantum Device); the magnetization of the samples was measured under 2 Tesla, in the temperature range 5-300 K. Fig. 5 shows the thermal variation of the inverse molar susceptibility for various compositions. The magnetic data are reported in Table 1. All samples exhibit a paramagnetic behavior (CurieWeiss-type) for x--<0.40 over the whole range of temperature and for x->0.50 above 50 K. However, at rising values of x(Mn), [0p[ values increase, which means that magnetic interactions intensify. Starting from the experimental values of the Curie constants and assuming the spia only

"1

15.751 ~15.SS4 3"15"35

J

.....-~-"~'-"'-"~

3.98~, 3.94

. ~

b

3.90

X

1.00

Fig. 3. Variation of the unit cell parameters and volume of the Bi~V~_,Mn,OH_~ phases.

237

M. Alga et al. I Journal of AIIo"s and Compounds 256 (1997) 234-243

8.00

7.90 t

7 71 7.601

......

~ .

/

7.50 t

g

!

7.40T

.

0.00

0.20

0.40

0.60

1.00

0.80 x

Fig. 4. Composition dependence of the measu~d and calculated specific mass of the Bi4V:_,Mn.O._ ~ phases.

RsO.ZO

40o--.I

jr

x : O.SO

o.

|

x = 0.40

0.(,0

0

Ioo

too

Ioo

T~2__ Fig. 5. Thermal variation of the inverse molar susceptibility of various Bi4V,_Mn~+,Mn,4+O. .... t: compositions.

238

M. Alga et al. I Journal ~ Alloys and Compounds 256 (1997) 234-243

Table I Magnetic data of various Bi4V:_,Mn~" Mn~÷O,~..... : composition,; x

CIMn"

0.20 0.30 0.40 0.50 0.60

2.99 2.7,1) 2.7![ 2.7([I 2,6~g

Op(K)

-

-4.7 - 5. I -6.8 -9.0 30.0

r(Mn4. )~

8"

0.0 0.23 0.22 0.27 0.28

0.20 0.26 0.35 0.43 0.51

Experimental Carie constant per I Mn cation. h T=yl.t. • *5=x--y12.

values to be, for Mn ~ ', C = 3 and for Mn ~+, C = !.875, it clearly appears that manganese cations are in mixed valence state (Mn 3+, Mn 4+) (Table 1). The Mn 4+ content and the oxyge)n vacancy number were then calculated for each composition studied (Table 2). Both increase slightly with increasing x. The studied compositions can consequently be written: Bi4V,_.,Mn3+>. Mn>4+ Oil ...... ./., (6= x-y/2). In agreement with Goodenough et al. [10], the anion vacancies are assumed to be disordered in the ~t-phase and located in the axis sites apical to vanadium and manganese cations. In addition, the substitution of manganese for vanadium leads to create additional five-fold coordinated sites of C~, symmetry in which Mn 3+ cations of t2~ ' d~ electronic configuration (so-called Jahn-Teller cations) are well stabilized [13-15]. The size difference between the investigated cations is not large enough to account for the strong increase of the c parameter with increasing x, which is also influenced by the simultaneous creation of vacancies. The increase of the number of anion vacancies results, for electrostatic reasons, in an increase of the distance between the ( B i , O , ) 2+ layers and the oxygen ~+ " Mn,.~2 ~)+ 0 3.5-x/2+v/4] . 2- perovdeficient ttV t-~z2 M n(,_>.)/2) skite-like slabs. The presence for x>0.20 of manganese cations in mixed valence involves a lower increase of the oxygen vacancy number with [ncreasing x than if all manganese cations were trivalent. The number of vacancies in the (x=0.50) composition is smaller than the 0.75 (Table 2), limit, which would be reached if all manganese cations were Table 2 Formulation of various Bi~V.,_.Mn~*_,Mn~'Oll_,.,,., compositions x=0.20

Bi4v, ~Mn,'b',,O,,~,,I-1,:. [Bi,O.,1""[V,,~,)Mni~~.O, ~,,[3,)~,,]:-

x :0.30

Bi,V, ,,,Mn~'.,,Mn~~,,O..... [:], .,~ [Bi,O21"'lV. ,~Mn,~;,Mn,',;~,O,.n,).d:-

x = 0.40

r e . v , .,Mn~,;,M.,',;~O . . . . O ,

,~ IBi.,O_,l ""[V,,,,)Mn;',;,Mn~~,,O, ,:El. J " -

:0.50

ai.v, ..,,M.~,;~M.,',LO,,, ..O... lBi.,O.,l~"iV,,,,Mn~,~,Mn~,;,O, ,,El,, ~:l:-

x =0.60

Bi,V, ,.,Mn;');,Mn~;70,) 4,1~.... IBi20.,l:*IV,,,,,Mn~,LMo,',;~,O,,,t~,, ,~1:-

trivalent. On the contrary, it is slightly higher than 0.75 in the (x=0.60) composition, which belongs to the solid solution (0.50
4. Elaboration of ceramics The powders obtained are pressed to form disks of 12 mm in diameter and about 2 mm thickness. The pellets are then sintered, in air, according to the following conditions: - introduction of pellets into the furnace, the temperature of which has been first stabilized at the sintering temperature T,. - quenching of pellets from T,. Fig. 6 shows the temperature dependence of the shrinkage for ceramics of Bi4Vi.sMno.2Oio.s composition: the sintering starts at about 630 °C, it reaches a value of 7% at 840 °C. The influence of the sintering time on the ceramics shrinkage has also been studied at different temperatures close to T~ (Fig. 7). Finally, the sintering conditions selected have been the following: T = 8 5 0 ° C , sintering time > 2 h. The density of ceramics obtained is about 91%.

5. Electrical properties 5. !. Determination o f the total conductivity, ~ ....

Conductivity measurements have been carried out in air on pellets sintered at 850°C during 15 h and quenched from that temperature. Vacuum evaporated gold has been used as electrode material. The total conductivity, ~o,., has been determined by the complex impedance method. The impedance of materials has been measured as a function of frequency using a Solartron 1260 frequency response analyzer: the bulk resistance relative to a given temperature is determined by extrapolation of the Z ' = f u n c t . ( Z ') diagrams at the phase angle (¢,) equal to zero. The frequency range used was 1-106 Hz; measurements were carried out between 25 and 240 °C. 3+ Mn,.4 . O~t_~+,./, . The Bt•4V2_xMn~_,~ compositions studied are these which have been the subject of magnetic measurements. The presence, with increasing x, of a larger number of vacancies in the perovskite-like sheets (Table 2") might suggest a larger mobility of oxygen ions.

239

M. Alga et al. / Jottrnal of Alloys and Compounds 256 (1997) 234-243

t('C)

2po

0.01 l

4oo

6oo, . . . .

890

xooo,

-0.01 !

I < - 0 . 0 5 -~

-0.07

!

-0.09J

Fig. 6. Temperature dependence of the shrinkage

for ceramics

of Bi~V;~Mn,,.,O,. s composition.

time (min.) o.ol

s?

loo

1~o

2q0

2sp

30o

-0.01

-0.03 2

-0.05

T8 800oc 830*C

-0.0"/i~

840"C 850"C

-0.09 J Fig. 7. Influence of the sintering time on the shrinkage of ceramics of Bi~V, xMn~,:O,,,x composition at various 7". temperatures.

240

M. Alga et al. I Jmmud of AIh~vs and Compounds 256 (1997) Z~,1-243

Fig. 8 gives the variation of the total conductivity, t%,, as a function of temperature for the samples studied. A non-linear leasl: squares analysis was applied for fitting the experimental daia to an Arrhtzaius-type equation: ~r,,,,.= ~ ) e x p ( - A E , / k T ) . Whatever the x value is. a good agreement has beetlL obtained in the considered temperature domain (R=0.g8). Inside the (0.15-
X(xj a t O t .

(a.¢m) -1

\

The (x=0.60) composition, of orthorhombic symmetry, shows electrical performances much lower than these relative to Bi4V2_~Mn~_+y Mn~ + Oil .... ,./, (0.15<--x--<0.50) compositions (Fig. 8 and Table 3). These weaker performances could be explained by the existence of an ordering of vacancies at long range inside the (0.50--
Taking into account the presence of two oxidation states of manganese cations, the existence of an electronic conductivity may be supposed and therefore d.c. measurements of samples using the four points method were achieved [211. The measurements have been carried out on pellets sintered in the same conditions as those used for the determination of (r,,,,. Fig. 9 shows, for studied samples, the variation of log o-~ with temperature. In the temperature domain considered. the temperature dependence of o- is of Arrheniustype: o'~=O'~n e x p ( - A E J k T ) . Inside the Bi4V.,_,Mn~ , Mn~ ÷ O i l _ , + , / -, phase (0.15~x<-0.50) of 3,-Bi~V.,Oii structural type, AE~ appears as independent of x. On the other hand, for a given temperature in the temperature range studied, o'~ does not depend on x in the (0.20--
The temperature dependence of ionic conductivity, ~ , deduced from these of ~ , , and ~ , is given in Fig. 10 for all studied samples. The values of activation energies corresponding to ionic and electronic contributions, AE i and AE~, respectively, are collected in Table 3. On the other hand, the variation of log o'.~00 K with x is simultaneously represented for o'to~, ~ and o-~, in Fig. 1 I. These materials, in the experimental conditions where measurements have been carried out, e.g., in air, are mixed conductors. Table 3 Activationenergies, AE, and AE. for some Bi4V: Mn~ :,Mn~" O. -,.,,.. compositions

-

IO00/T(K)

. . . .

I 1.o

~ 2

Fig. 8. Ternperalture dependence of MnI" Mn~'O ....... _. compositions.

l

5

_

3.0

~,,,

for some Bi4V.,_,-

x

AE, (eV)

AE~ (eV)

0.20 0.30 0.40 0.50 0.60

0.77 0.70 0.75 0.79 1.03

0.72 0.72 0.70 0.74 0.77

M. Alga et al. l Journal of Alloys and Compounds 256 (1997) 234-243

loq % (O.cm) - I / ' /

•.

241

Ioq o i (~.cm) -I

0.30 -3

-3 •.

0.20

0.20

-4

- 0.30

• .e.se • - 0.30 -S

• ~

• .O~SO

o~0 o.4o

x -

-? Il

L. _ _

IO00/TIKI

+.'s

,.:

z.' s

Fig. 9. Temperature dependence of o- for some Bi,V:_.Mn~',Mn,"O . . . . . . : compositions.

The variation of ~ with x differs from that of o"c (Fig. il): as a matter of fact. ~ decreases quickly with increasing x in the (0.20-0.30. On the contrary, o"c is quasi-constant in the (0.20--
.7 i .--

I 1.5

2000/TIK) !

| 2.0

Fig. 10. T e m p e r a t u r e dependence Mn~,Mn~'O . . . . . . . compositions.

2.S

of

¢,

for

some

Bi+V:_ ,-

occupy the c-axis sites apical to V 5+ and M "+ cations. They have shown that the two-dimensional motions of the apical oxide ions inside planes perpendicular to the c-axis result from the ability of the V 5+, Ti 4+ and Nb 5+ ions to adapt readily to changes in coordination by a simple ferroelectric-type displacement along the c-axis and Cu 2+ ion to accept four. five or six oxygen neighbon; [10]. Such a behavior can consequently be also attributed to the Mn 3+ ions in Bi4V~ 8Mn020,,_~, the electrical performances of which are comparable with these of Bi4Vj.sMo.2Oll_ ~ (M=Ti. Cu. Nb) [I0].

6. Conclusions The study of the influence of the replacement of vanadium by manganese on the structural prope~ies of Bi+VeO,, has allowed us to isolate at room temperature a solid solution of a-Bi+V20,, structural type for ( 0 < x < 0.15) and a solid solution of ~-Bi4g2oll structural type for

242

M. Aly.a et al. I Journal of AIh~.vs and Compound*" 256 (1997) Z~4-24.:1

log o500K (O'cm)-I

-4

i

x 0.20

0.30

0.40

0.50

Fig. I I. Variation of log tr,,,,, ~ as a function of x for o',,,,. ~. and ~.

(0.15<--x<-0.50), Beyond 0.50, an orthorhombic distortion o f the unit cell has been shown in the (0.50
in the manganese-substituted phase play a similar role to that o f Ti 4+ and Nb ~+ ions in the homologous phases.

References [I] B. Aurivillius, Arkiv. Kemi.. I 11949) 463. [2] J. Goplarkishnon. A. Kamanan and C.N.R, Rao, J. Solid State Chem.. 55 (1984) IOI. [3] A.V. Firsov, A.A. Bush, A.E. Mirkin and Y.N. Venet~v, Kristallografiya. 30 (1985) 932. [41 A.A. Bush. V.G. Koshelayeva and Y.N. Venevtsev, Ipn. J. Appl. Phys.. 24 (1985) 625. [5] A.A. Bush and Y:V.Venevtsev, J. Inorg. Chem.. 31 (1986) 769. [ ,] Y.A. Blinovskov and A.A. Fotiev, Zh. Neorg. Khlm.. 32 (1987) 254. [71 F. Abraham. M.F. Debreuille-Gres~, G, Maires~ and G. Nowogrocki, Solid State Ionics. 2 8 - 3 0 (1988) 529. 18] F. Abraham. J.C, Boivin, G. Mairesse and G. Nowogrocki. Solid State Ionics, 40-41 11990) 934, [9] V. Sharma, A.K. Shulka and J. Gopalakrishnan, Solid State hmics. ¢~' (t992) 359.

M. Alga et al. I Journal of Alloys anU Compounds 256 (1997) 234-243

[10] J.B. Goodenough, A. Manthiram. M. Paranthaman and Y.S. Zhen, Mater. Sci. Eng. B. 12 (1992) 357. [I I] R.N. Vannier. (3. Maires~, G. Nowogrocki, F. Abraham and J.C. Boivin. Solid State Ionics, 5 3 - 5 6 (1992) 713. [12] R. Essalim. B. Tanouti, J.P. Bonnet and J.M. R6au. Mater. Left.. 13 (1992) 382. [13] P. Hagenmuller. M. Pouchard and J.C. Grenier. Sol,:d State Ionic.~. 43 (1990) 7. [ 14] K,R. Poeppelmeier. M.E. Leonowicz and J.M. Longo, J. Solid State Chem.. 44 ( 19821 89. [15] %/. Caignaert. N. Nguyen. M. Hervieu and B. Raveau, Mater. Res. Bull.. 20 (1985) 479.

243

[16] D. Komyoji, A. Yoshiasa, T. Moriga, S. Emuva, F. Kanamaru and K. Ko/o. Solid State Ionics. 50 (1992) 291. []7] D.W. Stfickler and W.G. Carlson, J. Am. Ceram. Soc.. 48 (1965). 286. [18] T.Y. Tien and E.C. Subbarao, J. Chem. Phys.. 39 0963) 1041. [19] J.M. Dixon, L.D. Lagrange. U. Merten, C.F. Miller and J.T. Porter, J. Electrochem. Soc.. 3 { 1963) I I0. [201 F. MoTtarzadeh, J. Mater. Sci. Left.. 6 (1989) 1385. [21] ,I. Laplume. Onde Electrique. 35 (1955) 355. [22] n Yon and M. Greenblatt, SaIM State Ionics. 81 (1995) 225.