Anisotropic diffusion of oxygen in Nd2CuO4−δ single crystal

glllg ELSEVIER

PhysicaC 222 (1994) 333-340

Anisotropic diffusion of oxygen in Nd2CuO4_asingle crystal Yasushi Idemoto, Kiyoshi Uchida, Kazuo Fueki Department of Industrial Chemistry, Facultyof Science and Technology, Science Universityof Tokyo, Yamazaki, Noda-shi, Chiba 278, Japan Received 25 March 1993;revised manuscript received22 December 1993

Abstract

Single crystal was grown by the TSFZ method, and the chemical diffusion coefficients of oxygen,/),~ in the a-b-plane and/~c in the direction of the c-axis were determined by means of a thermomierobalance. The Arrhenius plot for/~,~ showed a break at 800" C, which was interpreted as the effect of surface reaction below 800°C. Above 8000C,/~p.lycalculated from/~*band/~c was almost the same as the measured one. The vacancy diffusion coefficients of oxygen,Dr(c) and Dv (ab), were calculated from the chemical diffusion coefficients,/~ca n d / ~ . The anisotropy of vacancy diffusion was small. This might be due to the nearly equal jumping distance of the oxide ion vacancy in the a-b-plane and in the direction parallel to the c-axis.

1. Introduction

2. Experimental

It has been found that the critical temperature Tc of superconducting oxides is controlled by the oxygen content, more precisely, the amount of nonstoichiometric oxygen [ 1-8 ]. In order to determine the oxygen-annealing condition under which the oxygen content is controlled, the data of oxygen nonstoichiometry as functions of temperature and oxygen partial pressure and of oxygen diffusion are necessary. In the previous paper [ 9 ], the authors and their co-investigators have carried out a study on oxygen diffusion in polycrystalline Nd2CuO4_6. Since the properties of high-To superconductors are anisotropic [ 10 ], the anisotropy is anticipated for the diffusion of oxygen in NdzCuO4_6. The purpose of the present study are, first, to grow a large NdzCuO4_6 single crystal of high quality by the travelling solvent floating zone (TSFZ) method, and secondly, to determine the chemical diffusion coefficients of oxygen in the a-b-plane and in the direction of the c-axis, to get information on anisotropic diffusion of oxygen.

2.1. Crystal growth and characterization

Nd203 powder of 99.9% purity was mixed with CuO powder of 99.9% purity in a molar ratio of N d : C u = 2: 1, and the mixture was grounded in the presence of a small amount of ethanol. After drying, the mixture was heated at 850°C in air for 24 h. The resulting powder was pressed into a rod, 5-7 mm in diameter and 6 cm in length, under a pressure of 2-4 t / c m 2 by means o f a CIP apparatus. The rod was sintered at 1000° C in a stream of oxygen for 12 h and used as a feed rod. The solvent material was prepared by the copreeipitation method from a nitrate solution in which the metal constituents were contained in a molar ratio of N d : C u = 3:8.5. An oxalic acidethanol solution was employed as the precipitation reagent. The precipitate was heated at 400 °C in air to convert it into oxide, which was heated at 850°C for 24 h to form Nd2CuO4_&The oxide powder was pressed into a rod by means of a press and was used

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Y.Idemoto et al. / Physica C 222 (1994)333-340

as solvent. An apparatus with twin ellipsoidal mirror (SC-N35HD, Nichiden Machine Manufacturing Company) was used for the single crystal growth. Two-750W halogen lamps were used as heat source. The X-ray back reflection Laue method was employed to examine the quality of the grown single crystals and to determine the orientation of the crystal. Properly grown boules were cut into a rectangular shape surrounded by (100), ( 0 1 0 ) and (001) planes by means of a wire saw using SiC slurry and the specimens were polished using 1 gun diamond slurry. A portion o f single crystal was dissolved with concentrated hydrochloric acid and the solution was diluted with water. Then, the metal composition was determined by the ICP method. The lattice parameters were determined from the X-ray powder pattern using the RIETAN program for Rietveld analysis.

W(t)

W(oo)

w(0)- w(~)

-

512 -~-~-e x p ( - k t )

( 1)

where W(0), W ( t ) and W(oo) represent the weights at times 0, t and infinity, respectively, and k is a rate constant of redox reaction controlled by the diffusion. If the chemical diffusion coefficients f oxygen in the a-b-plane and in the direction of the c-axis are represented by 13~ a n d / ~ respectively, k is written as [9,11,12] n2l/~c +

1

1

-

where 2m and 2n are two sides of the a-b surface and 2l is thickness. Using Eq. ( 1 ), one can calculate kt from [ W ( t ) - W ( o o ) / W ( 0 ) - W(oo) ] at time t. The plot of kt against t provides k, and one can get a set of data between k and 1, m and n from which/~c and LSabcan be obtained.

2. 2. Determination of chemical diffusion coefficient o f oxygen 3. R e s u l t s a n d d i s c u s s i o n

Three rectangular singlecrystalswith differentsizes were used for the determination of the chemical diffusion coefficient of oxygen. A specimen was suspended from a microbalance and equilibrated under a predetermined oxygen partialpressure and temperature. Then, the oxygen partialpressure was changed stcpwise, for example, from 0.3 to 0.01 atm or in the reverse direction, and the weight change was followed with time. W h e n the specimen has a size of 21×2mX2n and the redox reaction is controlled by the diffusion of oxygen, the weight change-time curve is expressed, as the fwst approximation, by [9,1 I,12 ]

3.1. Characterization of grown crystals Fig. 1 shows a grown boule, 4 mm in diameter and 100 mm in length. The grown boule had an elliptical cross section and the surface of the upper half of the crystal had black and bright luster. When the incident beam was in the direction perpendicular to the growth direction and parallel to the short axis of sectional ellipse, the back reflection pattern was four-fold rotation symmetry, as shown in Fig. 2 (a), and its was concluded that the direction of the incident beam coincided with that of the c-axis. Then, the rod was fixed

lcm Fig. I. As=grownboule of Nd2CuO,)_,w.

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Y. Idemoto et al. / Physica C 222 (1994) 333-340

on a square glass plate of two sides A and B so that the directions of c-axis and crystal growth coincided with sides A and B of the glass plate, respectively. The plate was placed vertically so that side A was contacted with the horizontal fiat surface and the normal of the plate coincided with the X-ray beam. Then, keeping side A on the horizontal plane, side B was tilted. When the tilt angle was 45 °, the two-fold rotation symmetry pattern, shown in Fig. 2 ( b ) , was found. Accordingly, the direction of the incident beam was considered to coincide with the normal of the (100) plane. From these results, the growth direction was identified to be ( 1 1 0 ) . The ICP study re-

(a) (001) plane

vealed that the crystal had a composition of N d : C u = 2.00:1.00 and the result of Rietveld analysis showed that a-- 3.9409 ( 2 ) ,/~ and c = 12.1574 ( 7 ) A. The size of the crystals used for the diffusion study is given in Table 1. 3.2. Chemical diffusion coefficients o f oxygen

Fig. 3 shows the relaxation curves at 900°C when the specimen was reduced or oxidized. The change in oxygen partial pressure was made stepwise from 0.3 to 0.01 atm. The curves agree with each other and the normalized weight change is exponential with time. The redox reaction of solid consists of two elementary processes, the surface reaction at the gas-solid interface and the diffusion in the solid. The surface reaction is strongly dependent on the oxygen partial pressure, while the diffusion is not. Since the chemical diffusion coefficient is derived from the rate constant of the diffusion-controlled redox reaction of solid, the fact that the redox reaction is controlled by the diffusion process should be confirmed. When the reaction is diffusion-controlled, the rate constant is independent on the oxygen partial pressure. Accordingly, the relaxation curve due to oxidation caused by the change of oxygen partial pressure should coincide with that of reduction, namely the reaction in the reTable I Dimensions of the Nd2Cu04_o single crystal Sample

21 (era)

2m (cm)

2n (era)

1 2 3

0.2450 0.2483 0.3320

0.4219 0.3792 0.3419

0.878 1.373 1.292

1.0 O : ]geductloumnnl(O.3~O,Olatnn) • : Ozldntlonn ruun(O.Ol~O.3atm)

I;

i O~

(b) (100)plane Fig. 2. Back-reflectionLaue patterns ofNd2CuO4_8. (a) (001) plane, (b) (100) plane.

1000 t/m

Fig. 3. Weight relaxation curves of Nd2CuO4_8 single crystal in oxidation and reduction runs at 900°C.

336

Y. ldemoto et o2./Physica C 222 (1994) 333-340

verse direction. However, when the redox reaction is surface reaction-controlled or mixed-controlled by the surface reaction and diffusion, the partial oxygen pressure dependence reflects the relaxation curve, and the oxidation curve disagrees with the reduction one. Several papers [ 13-15 ] concerning the chemical diffusion experiment have reported disagreement o f the in-diffusion chemical diffusion constant with the outdiffusion one, or hysteresis o f cycled oxidation and reduction. Their chemical diffusion coefficients determined f r o m such relaxation curves are not correct because the surface reaction rate is included. In the present work, the relaxation curve due to oxidation coincides with the reduction one. It is concluded that the redox reaction in this study is controlled by the diffusion o f oxygen. Fig. 4 gives the relaxation curves o f specimen 1 at different temperatures. The relaxation time becomes smaller as the temperature becomes higher, kt calculated from [ W ( t ) - W ( o v ) / W ( 0 ) - W(ov ) ] and Eq. ( 1 ), is plotted against t in Fig. 5. All the data fall on the straight lines and from .

1.0

.

.

. V : 7lOOt

I~'~\

~x: .ooc 0

¢1¢

: 8SOOC

.:,,+<+

the slope, k was obtained. Using the k, l, m and n values and Eq. (2),/~ab and/~c, the chemical diffusion coefficients in the a-b-plane and in the direction fo the c-axis, respectively, were calculated. Table 2 summarizes the chemical diffusion c o e f f i c i e n t s / ~ and /~c. The Arrhenius plots for/~ab and/~c are given in Fig. 6, and the Arrhenius equations above 800°C are represented by .~ab(cm2 S-1 ) ( ( 2 1 + 2_) kcal/mo!~ = 2 . 4 0 X 10 - t exp RT ],

s-')

=9"88X10-2exp( - (21-+2-)Lcal/m°!'~RT /.

(4)

Table 2 Chemical diffusion coefficientsof oxygenin the Nd2CuO4_8single crystal T(°C)

/ ~ (¢m2s - ' )

~

900 875 850 825 800 775 750 725 700

1.17 X 10-s 9.71 X 10 - 6 8.51 X 10 -+ 5.94 X 10 - 6 4.99 X 10-6 4.20 X 10-6 3.21 X 10-6 2.049X 10-6 2.046X 10-6

3.50X 10-s 2.86X 10-s 2.40X 10-s 1.86X 10-s 1.54X 10-s 1.08X 10-s 7.89X 10-6 5.05X 10-6 3.39X 10-6

(cm2 s , ~)

T/~

Fig. 4. Weight releo~fio~ curves of Nd~Cu04_~ single crystal at different temperatures.

900 -3

1:

(3)

800

i

1.0

i

~

' fi~Q~,

700

i

~

i

.

.

i

.

.

i

~

-6 A : 7sOC~

0

•

,

-0.5

0

i 1000

,

i 2000

: 77Joc

v : :eeoc 3000

t/sec Fig. 5. Relation between ktand tfor Nd2CuO4_j single crystal,

-7

8

~

,

,

,

I

9

,

~

,

,

I

10

,

,

,

11

T'z/10"4K "z

Fig. 6. Arrhenius plot for/~,~, ~c and L3~yof Nd2CuO4_o single crystal. (11) J~b, (D)/~, ( • ) J~po~y(calc),(O) ~po~(obs) [9].

337

Y. Idemoto et al. / Physica C 222 (1994) :733-340

It was found that aa~, the in-plane conductivity of Nd2CuO4_6, is three orders of magnitude larger than ao the conductivity in the c-direction, over the wide range of temperature of 500-850 oC [ 16 ]. This result indicates high anisotropy of electronic conduction. However, ~ the chemical diffusion coefficient in the a-b-plane is only three times larger t h a n / ~ , the chemical diffusion coefficient in the c-direction, which indicates that the oxide ion movement is threedimensional rather than two-dimensional. The chemical diffusion coefficient of oxygen in polycrystalline Nd2CuO4_~ [9] is also given in Fig. 6. The Arrhenius equation is

/~po,y(Cm2 s-l ) 0 -2 e x p ( - ( 16 + 5~-y ) kcal/mol'-). / 1 o96× 1

In previous papers [ 3,9 ], the authors have determined the oxygen nonstoichiometry of Nd2CuO4_6 and NdLssCe0.~sCuO4_~ as a function of oxygen partial pressure and temperature by means of a microbalance and found that these oxides have an oxygen deficit. Accordingly, it was concluded that the vacancy mechanism prevails in the oxygen diffusion in these oxides. W h e n the vacancy mechanism prevails, the chemical diffusion coefficient/~ is related to the vacancy diffusion coefficient Dv by [ 9,18 ]

(5)

(6)

(8)

where Cv is the vacancy concentration. As the thermodynamic factor (~lnPo2/OlnCv) can be calculated from the oxygen nonstoichiometry data [ 9 ], one can calculate Dv(ab) in the a-b-plane and Dr(c) in the direction of the c-axis from Eq. (8). They are given below and in Fig. 7.

where/~m,/~2 and/~3 are the diffusion coefficients in three principal axes, and a, fl and y are the directional cosines. If Eq. (6) is applied to Nd2CuO4 _ ~ of tetragonal structure, the diffusion coefficient of sintered body is given by /~poly= ]/~ab + ~/~

fOlnPo, \ ~-T~--~ a / '

~=-"

When the diffusion is anisotropic, the overall diffusion coefficient in polycrystalline solid is represented by [9,17] /~poly = O/2J~ 1 "~"~2J~ 2 "~"~2/~ 3

3.3. Vacancy diffusion coefficients of oxygen

-4

(7)

The chemical diffusion coefficient in sintered body, /~poly(calc.), was calculated using Eq. ( 7 ). The result is also shown in Fig. 6 by solid circles and agrees well with the observed one. Above 900 ° C, a slight linear weight decrease was observed. In our previous work [ 3 ], a similar weight decrease and the formation of Nd203 o r CeO 2 were observed for NdLssCe0.tsCuO4_6 and the evaporation of copper oxide was concluded. Probably a similar evaporation would occur above 900°C in the present case. As mentioned above, when the relaxation curve shows the hysteresis in the oxydation-reduction cycle, the reaction is surface reaction-controlled or mixed-controlled. Below 800°C, a slight hysteresis was observed. Probably, the break o f / ~ observed at 800°C, would be caused by the transition from the diffusion-controlled reaction to the mixedcontrolled one.

~"

-5

E u~

o

-6

-7

I

I

I

8

9

10

11

T'I/10"4K "1

F~. 7. Arrhelfius plot for Dv(ab), Dv(c) and Dv(poly). Nd2CuO4_~ (0) Dv(ab), ( ~ ) Dv(c), ( A ) Dv(poly) [9]. Lal_xSr~CoOa_8(poly) [191: (O) x--0, ( 1 ) xffi0.10. La~_~Sr~FeO3_~(poly) [20]: (O) x=0, (D) x=0.10, (V) x=0.25. ( • ) : (Ndo.eegCeo.136Sro.19s)zCuO4_8(poly)[25 ].

338

Y. ldemoto et al. / Physica C 222 (1994) 333-340

the long jumping distance and the passing through a point between two Nd 3+ ions.

Dv( ab ) ( cm 2 s - 1 )

=2.19XlO_2exp (

(18+4)~ -kcal/mol' ~ )I,

-

(9)

D r ( c ) (cm ~ s-~ )

=l.30Xl0_2exp ( -

3.4. Selfdiffusion coefficients of oxygen

In the case when the vacancy mechanism prevails, the self-diffusion coefficient D is related to Dv by

(19_+2) kcal/mol~ ~y )(10)

It has been found that the oxygen vacancy diffusion coefficient of perovskite-type oxide has nearly the same value and activation energy of around 18 kcal/mol [ 19,20 ]. The results are also given in the same figure. The data for Nd2CuO+_6 agree well with those for the perovskite-type oxides. This agreement evidently shows the oxygen diffuses by the vacancy mechanism as in the case of the perovskite-type oxide. The crystal structure of Nd2CuO+_~ is given in Fig. 8. Since the oxygen movement in perovskite proceeds by the successive jumps of a vacancy from one site to the neighboring, the in-plane vacancy diffusion would occur, for example in such a way as, from site A to site B in the O-plane and from site C to site D in the CuO2 plane. In the c-direction, the vacancy would arrive from A to F via E. Since, r~,=2.79 A and re= 3.04 A, the jumping distance from A to E is a little longer than ra. A slightly small absolute value Dr(c) compared to Dv(ab) would be the result of

where C and Cv are the concentration of oxide ion and vacancy, respectively. Accordingly, one can calculate D from Cv which is determined from the oxygen nonstoichiometry data suing Dv given in (9) and (10). D(ab) and D(c) for Nd2CuO4_~ are given by D (ab) = 5.52 X 10-2 e x J - - (32 + 5) kcal/mo!' ~ RT ]' (12) D(c) = 3.26X 10 -2 exp

respectively, and their plot is given in Fig. 9. The tracer diffusion measurement on single crystals of high-To superconductors has been carried out so far -4

I

I

I

I

1

-10 -12 -14

~

r~=3.o4~

~

~ [ ~ Oxygen Vacancy

+j+j ,, "" (_,

I

-8

"~

Cu

I

-6

0

~

- (33 _+3) kcal/mol~ ~ ), (13)

C

0

(11)

DC = Dv Cv ,

i,

Fig. 8. Crystal structure of Nd2CuO4_6.

o -16 -18 6

I

I

I

I

t

t

8

10

12

14

16

18

20

T q/104K "1

Fig. 9. Arrhonius plot for D(ab), D(c), D(poly), D*(ab) and D*(c). Nd2CuO+_6: (0) D(ab), (<>) D(c), ( A ) D(poly) [9]. YBa2Cu3OT_6: (Q) D*(ab) [21 ], (O) D*(c) [21 ], (m) D*(ab) [22], (E3) D*(c) [22]. Bi2Sr2CuOy: (W) D*(ab) [23], (V) D*(c) [23]. Bi2Sr2CaCu2Oy:(A) D*(c) [24].

Y. Idemotoet al. / PhysicaC 222 (1994)333-340 only for YBCO, Bi2201 and 2212, because of the difficulty of single crystal growing. The tracer diffusion coefficient D* is also given in Fig. 9. Between D and D*, there is a relation D*ffD,

(14)

where f i s the correlation factor, which is calculated on the basis of the diffusion mechanism and crystal structure. In most cases, f i s less than unity. It is noteworthy that the activation energy and the absolute value of D(ab) for Nd2CuO4_6 are nearly the same as D* (ab) for YBCO [21,22 ] and Bi-2201 [23]. This fact indicates that the diffusion path is alike for all three kinds of oxides. As to D(¢) and D*(c), D(c) for Nd2CuO4_6 is several orders of magnitude larger than D * (c) for YBCO [ 21,22 ], Bi2201 [23] and2212 [24] in a low-temperaturerange. Since both Bi-2212 and 2201 phases have the (BiO) 2 block with rock salt type and excess oxygen [4,5 ], the concentration of oxide ion vacancy is low. Accordingly, D*(c) would be low. D*(c) for YBCO also increases with increasing temperature. In the case of YBCO, the oxygen vacancy has to pass through the C u ( I ) , BaO, CuO2, Y, CuO2 and BaO planes via oxide ion sites. Because the structure of the block consisting of CuO2-Y-CuO2 is similar to CuO2-CaCuO2 in the Bi-2212 phase, the vacancy concentration of BaO planes seems to be low at low temperatures and increase with increasing temperature.

339

(3) The chemical diffusion coefficients of oxygen in a polycrystalline oxide were calculated from/~,b and /~c, and compared to the observed result. Good agreement was found. (4) The vacancy diffusion coefficients, Dv(ab) and Dv (c), were calculated. (5) The self-diffusion coefficients D ( a b ) and D(c) were calculated and compared with the tracer diffusion coefficients D*(M~) and D*(c) for YBCO and Bi-2201 and 2212 single crystals.

Acknowledgements This work has been partly supported by a Grantin-Aid for Scientific Research on Priority Areas, "Science of High-To Superconductivity" given by the Ministry of Education, Science and Culture, Japan. The authors wish to thank T. Nakamura and T. Yanagida of the Tokyo Institute of Technology and IC Kishio of Tokyo University for their advice on the fabrication of single crystals. The authors wish to acknowledge H. Ishizuka and M. Nishizaki for their experimental assistance.

References [ 1 ] K. Fueki, K. Kitazawa, IC Kishio, T. Hasegawa,S. Uchida,

4. Conclusions ( l ) Nd2CuO4_a single crystal of high quality, 4 m m in diameter and 10 cm long, was grown by the TSFZ method. (2) Using the single-crystal specimens of rectangular shape, the chemical diffusion coefficients of oxygen, / ) ~ in the a-b-plane a n d / 3 c in the direction of the caxis, were determined as follows.

]~ab(cm 2 s - '

)

=2.40)< 1 0 - ' e x p ( -

(21 __.2) kcal/mol~

/"

/~c(cm 2 S-1 ) = 9 . 8 8 X 10 -2 e x p ( - - (21 _+2) kcal/mol~ /, \

H. Takagi and S. Tanaka, in: Chemistry of HighTemperature Superconductors, eds. D.L. Nelson, M.S. Whittingham and T.F. George,ACS Syrup.Series.Vol. 351, Am. Chem. SOc.,Washington, DC (1987) p. 38. [2] R.J. Cava, B. Batlog8,A.P. Ramirez, D. Werder, C.H. Chen, E.A. Rietman and S.M. Zahurak, Mater. Res. Soc. Symp. Proc. 99 (1988) 19. [ 3 ] Y. Idemoto, IC Fueki and T. Shinbo, PhysicaC 166 (1990) 513. [4] Y. Idemoto and K. Fueki, Physica C 190 (1992) 502. [5] Y. Idemoto and IC Fueki, Physica C 168 (1992) 167. [6 ] Y. Idemoto,S. Ichik~waand K. Fueki, PhysicaC 181 ( 1991 ) 171. [7] Y. Idemoto, Y. Itoh and K. Fueki, Physica C 202 (1992) 127. [8 ] H. Ishizuka,Y. Idemotoand K. Fueld, PhysicaC 195 (1992) 145. [9 ] Y. Idemoto,K. Fueki and M. Susiyama;J. Solid State Chem. 92 (1991) 489. [ 10] Y. Tokura, H. Takagi and S. Uchida, Nature 337 (1989) 345.

340

Y. Idemoto et aL / Physica C222 (1994) 333-340

[11] J.B. Price and J.B. Wagner, Z. Physik. Chem. 49 (1966) 257. [ 12] A. Nakamura, S.Yamauchi, K. Fueki and T. Mukaibo, J. Phys. Chem. Solids 39 (1978) 1203. [ 13] J.R. Lagraff and D.A. Payne, Physica C 212 (1993) 470. [ 14] J.R. Lalgraffand D.A. Payne, Physica C 212 (1993) 478. [ 15 ] J.R. Lagraff and D.A. Payne, Physica C 212 ( 1993 ) 487. [ 16 ] H. Ishizuk& Y. Idemoto and IC Fueki, Physica C 209 ( 1993 ) 491. [17]J. Crank, The Mathematics of Diffusion (Clarendon, Oxford, 1955) p. 7. [ 18 ] C. Wagner, Z. Phys. Chem. B 32 (1936) 447. [ 19 ] T. Ishisaki, S. Yamauchi, J. Mizusaki and K. Fueki, J. Solid State Chem. 55 (1984) 50.

[20] T. Ishis~d, S. Yamauchi and K. Fueki, Yogyo-Kyokai-Shi 95 (1987) 1031. [21IS. Tsukui, T. Yamamoto, M. Adachi, Y. Shono, K. Kaw~ata, N. Fukuoka, A. Yana~ and Y. Yoshioka, Physica C 185-189 (1991) 929. [22] S.I. Bredikhin, G.A. EmeFchenko, V.Sh. Shechtman; A.A. Zhokhov, S. Carter, R.J. Chater, J.A. Kilner and B.C.H. Steele, Physica C 179 ( 1991 ) 286. [23] M. Runde, J.L. Routbort, J.N. Mundy, S.J. Rot hman, C.L. Wiley and X. Xu, Phys. Rcv. B 46 (1992) 3142. [24 ] M. Runde, J.L. Routbort, S.J. Rothman, ICC. Goretta, J.N. Mundy, X. Xu and J.E. Baker, P h ~ Roy. B 45 (1992) 7375. [25 ] K. Fueld, Y. Idemoto and M. Sugiyama, Ann, Chim Fr. 16 (1991) 423.