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Self-diffusion in naphthalene single crystals

A. Bendani, L. Bonpunt

To cite this version:

A. Bendani, L. Bonpunt. Self-diffusion in naphthalene single crystals. Journal de Physique I, EDP

Sciences, 1993, 3 (4), pp.1059-1070. �10.1051/jp1:1993105�. �jpa-00246770�

(2)

Classification

Physics

Abstracts

61.708 66.30H

Self-dilTusion in naphthalene single crystals

A. Bendani and L.

Bonpunt

Laboratoire de

Cristallographie

et de

Physique

Cristalline (*), Universit6 Bordeaux 1, 351 Cours de la Liberation, 33405 Talence, France

(Received 6 October1992,

accepted

in

final form

4 December 1992)

Abstract. Molecular mobility in

organic

molecular

crystals

was studied

by

means of tracer diffusion

experiments

: self-diffusion of

naphthalene

into

naphthalene single crystals

was

measured. Wree self-diffusion tensors are determined from measurements in different

crystallogra- phic

directions, at three temperatures (338, 343 and 348 K). The

principal

axes and the

anisotropy

of self-diffusion are deduced. The

experimental

activation

energies

are determined and

compared

with results from the literature.

1. Introduction.

Solid state matter diffusion has been

widely

studied in many different

materials, metals,

semi-

conductors, halides, simple

oxides... Most of these materials

crystallize

in

high symmetry

structures, most often in the cubic space groups. Then diffusion is

isotropic. Organic crystals usually belong

to the lower

symmetry

systems, I-e-

orthorhombic,

monoclinic and triclinic.

Then diffusion is

anisotropic

and must be measured

by

a second rank tensor.

Experimental

methods issued from

crystal physics

must be

applied

in order to determine the diffusion tensor.

The present paper

reports

an

example

of such a

study.

We

present

a combination of classical methods of diffusion studies and tracer

counting technique,

which takes into account the

crystal

orientation and the

cutting

of

single crystal plates.

The

organic crystal

chosen is

naphthalene.

It is very

representative

of

organic

solids : the molecular

packing,

the space group

P211a,

and the

only

presence of van der Waals interactions are characteristic of a great number of this

type

of

crystals.

Moreover, it is

easily

obtained as

large single crystals

of

good

crystalline quality

and excellent

purity.

There is no

plastic phase

known between room

temperature

and the

melting

temperature at 353 K. Some

previous

studies on the same

compound [1-3]

were relative to self-diffusion in the

unique crystallographic

direction

c*, preventing

the

anisotropy

of self-diffusion to be determined in this

crystal.

The

study

of

diffusion

anisotropy

in the

crystal

of a very similar

compound,

anthracene, was

published

in 1965-66

[4, 5]. Only

two

crystallographic

directions were considered. A weak

anisotropy

was

(*) URA 144 CNRS.

(3)

detected ; but in these monoclinic

crystals,

the

complete

determination of the diffusion tensor needs four

independent

directions to be studied. A more recent

study [6, 7]

on heterodiffusion at infinite dilution of

2-naphthol

in

naphthalene single crystal

allowed the determination of the

heterodiffusion tensor at 343 K. A theoretical model

giving

a

partial interpretation

of the results was

proposed.

In this paper, the

experimental

method and the results of a self-diffusion

study

in

naphthalene,

carried out at three different

temperatures (338,

343 and 348

K)

are

presented.

The

microscopic interpretation

of these

results,

in terms of a vacancy model is

presented

in

anpther

paper which is devoted to the determination of the molecular

jump frequencies

from the

knowledge

of diffusion tensor.

2.

Experimental.

2,I PREPARATION OF DIFFUSION SAMPLES.

Naphthalene

was

purified by

zone

refining.

Single crystals

were grown

following Bridgman's

method. The detection and measurement of

impurity

content were obtained

by

gas

phase chromatography coupled

with mass

spectrometry.

The total

impurity

content of the final material is less than 5 ppm. The

crystalline quality

was

controlled

by

the

etch-pit technique [8, 9]

: no dislocation association in

subgrain

boundaries

was detected in our

samples,

and the dislocation

density

was about

10~ m~~ [9].

In order to

obtain the four

independent

coefficients of the diffusion tensor in monoclinic

crystals,

it is

necessary to

perform experiments

in four directions

(which

are not part of the same

plane).

Our tracer diffusion

experiments

were made on

parallelepipedic plates

of about

6 x 6 x 3 mm3. The

largest

face was

polished

in order to be

highly planar,

which is a

required

condition when

using

the classical treatment of a

planar infinitely

thin

deposit.

The diffusion

was studied in the direction

perpendicular

to the

polished

face. The well-known

cleavage along

the

(001) planes

of

naphthalene together

with a

simple optical

method

[10],

allows one to

identify

the a and b

crystallographic

axes of the monoclinic unit

cell,

and also that of c*

simultaneously perpendicular

to a and b. The orientation of the unit cell is determined

by

the

X-ray

diffraction

(Laiie) technique.

In order to

study

the

magnitude

of the diffusion tensor

along

these three axes, the

simple

orientation process described above is sufficient.

But,

on the other hand, if one wants to achieve the

complete

determination of the diffusion tensor in a monoclinic structure, the diffusion coefficient needs to be measured

along

another

crystallographic

direction : this xe direction was chosen such that it is contained in the ac

plane,

and it makes an

angle

of 135°

with a.

A

sample

was cut with a

plane

surface

perpendicular

to each direction. In order to obtain

parallelepipedic samples,

the

cutting

of the

Bridgman crystals

was carried out

by cleaving

with

a razor blade and

sawing

with a wire-saw. Good flatness of the diffusion

plane

was then

obtained with a microtome. The elimination of most of the dislocations

crqated during growth

and

cutting,

and caused

by

mechanical stress, was achieved

by submitting

the

sample

to a

thermal treatment in a stainless steel matrix at a temperature

just

below the

melting temperature (353 K).

This

annealing

consisted in

setting

the

crystal

for 8

days

at 348 K or 12

days

at 343

K,

and

cooling

it

slowly

over 3

days

to room

temperature (see

Tab.

Ii.

To prevent

sublimation,

the

plates

are surrounded

by naphthalene powder (which

minimizes the empty volume around the

crystal

in the

matrix).

After

annealing etching

studies indicated that the dislocation content was about

10~

m~ ~ on

the face

perpendicular

to the direction studied.

2.2 TRACER DEPOSIT AND DIFFUSION PROFILES. The marked molecule used was

naphthalene

14C-1(4, 5, 8) (specific activity

56

mcjmmole),

in

pentane.

The

deposit

method used

[I II

(4)

Table I.

Annealing

temperatures

(T~)

and

diffusion

temperatures

(T~).

TR

(K

343 348

Annealing

time 12 9

in

days

T~ (K)

338 343 348

Diffusion time 30 12 9

in

days

consisted in

deposing (three

or

four) drops

of the radioactive solution on a

glass slide, previously

cut

according

to the

sample

face dimensions. The sublimation of the radioactive

naphthalene,

which is made of very thin

grains,

took

place

after the very

quick evaporation

of pentane and induced us to

proceed

in the

following

way : first

siliconizing

the slide to get a

localized

drop,

then

cooling

the solution before

deposit

with

dry

ice.

The overall

deposit operation

must not exceed 30 s.

Afterwards,

the

glass

slide was tumed back to the

crystal

face and these two

pieces,

surrounded

by naphthalene powder (to

prevent

sublimation of the

sample),

were inserted into the matrix.

Thermal treatment was carried out from 200 to over 800 hours

(see

Tab.

Ii.

The time

necessary to reach the diffusion

temperature

and to cool the

sample

to room

temperature,

after the diffusion treatment, was short

(4 hi compared

with the diffusion time.

Following

the diffusion

period,

the

edges

were removed to avoid contributions from surface diffusion to the

activity

of each slice. The

crystal

was cut with a microtome. Four micrometer slices were removed each time and dissolved in ethanol. This solution was divided into two parts : the first one, to which a

liquid

scintillator was

added,

was used to measure the

radioactivity

of the slice

by counting

it in a

liquid

scintillation spectrometer. The second part of the ethanol solution was

analysed by

UV

absorption,

in order to eliminate errors due to an

imperfect

collection of the

whole slice. On the

spectra,

a

peak corresponding

to

naphthalene absorption

at 328nm

allowed us to detect a decrease in mass and

eventually

to correct the raw

radioactivity corresponding

to a

given

slice.

Every

slice

activity

was

proportional

to the concentration of

diffused

naphthalene

molecules.

The diffusion coefficient

(D)

was determined from the

slope

of the Ln

(A)

vs. x curve, where x is the

penetration

and A the

radioactivity

of each slice.

Figure

I shows a

typical

self-

diffusion

profile

in

naphthalene

at 338 K. The contribution of dislocations to the observed

mobility

was subtracted

by

Leclaire and Rabinovitch's method

[12, 13],

and the true bulk

diffusion coefficient

(D)

found.

Very

often this correction was not necessary as the

contribution of the dislocations could not be observed when their

density

is less than 0.9 x

10~

m~ ~ The

uncertainty

about the bulk diffusion coefficient is deduced from the

slope

of the linear

regression.

It is obvious that this method

only

allows for the

alignment

of the

points

on which the linear

regression

is made. In

fact,

this is more a

quality

factor of the measurement than its real

uncertainty.

The bulk diffusion coefficient characteristic of the direction

Dx;

studied was the result of several

experiments

carried out in the same direction and on different

samples.

For this purpose, the proper method consisted in

working

out a

single

curve

representing

the different functions Ln

(A~~,)= f(x~/t~).

A~~, is the

activity along

the

sample,

corrected for the

contribution of the dislocations. The factor

tj~

is a normalization factor which takes into

(5)

Loi

v.a.

~

a . corrected

. a not corrected

a

.

D "

D o

a

o soo

o

o

30

60 90 1 ~m

Fig,

I.- Self-diffusion

profile

in

naphthalene single crystal (t=720h, T~=338K, crystal

84, direction al.

account the different diffusion times of the different

experiments.

The same remark as for the

D about the

given uncertainty

can be made.

The

simplest

choice of the reference frame for our

study

is

(0,

xi, x~,

x~)

=

(0,

a,

b,

c*

).

We have made

experiments

in these three directions. The fourth one is xe as defined above.

3.

Experimental

results.

3.I BULK SELF-DIFFUSION COEFFICIENTS. Tables

2, 3,

4 show the bulk self-diffusion

coefficients obtained at

338,

343 and

348K, corresponding

to the directions xi, x~,

x~ and xe. The values of the coefficients obtained at 348 K and 343 K show, for a

given direction,

a

fairly

marked

dispersion

since the scatter between coefficients reach I to 2 x 10~ ~~

m~

s~ ~.

Impurities

in

quite

low concentrations

[9, III (the highest

does not exceed 30

ppm),

could not

explain

this

dispersion.

Due to this

fact,

we have realized two to five

experiments (usually four)

in order to obtain a suitable

precision

for each coefficient

Dx;.

At 0.99

T/(T~(K)

is the

melting temperature

of the

material),

the molecular

mobility

seems to be

higher

in the xi and xe directions

(3.4

and 3.8 x 10~ ~~

m~

s~

respectively).

The

same is true for the x~ and xe directions at 0.97 T~ and 0.96 T~, with 2.6 x 10~ ~~

m~

s~ and

1.7 x 10~ ~~

m~

s~ ~,

as average

respective

self-diffusion coefficients. We can notice a more

marked

diffusion

anisotropy

at 338 K than at 343 K or 348 K.

3.2 VARIATION OF THE BULK SELF-DIFFUSION COEFFICIENT WITH TEMPERATURE. At the

microscopic level,

we know that diffusion is most

probably

achieved

by

successive molecular

jumps

from an

occupied

site to a vacant site. If a

single

type of

jump

occurs, then D varies with T

according

to an Arrhenius law.

Conversely,

in a low symmetry

crystal

such as

naphthalene

where several types of

jumps

are

possible,

the variation of D with T does not

necessarily

follow this law.

But, given

the accuracy of the diffusion coefficients and the limited

temperature

range

[338 K,

348

K],

we can assume that the temperature

dependence

is

(6)

represented by

an Arrhenius law

(see Fig. 2).

With this

assumption

we obtain :

~ 74 kJ mol~

2 ~- l

~~l

~ ~'~ ~ ~~ ~~~

RT "'

~~ 46 kJ mol~

~2

~- i

~X2

~ ~.~ ~ ~~ ~~~

~T

D~~

=

14 x

ios

exp

~~ " '~~°~~

m~

s~

RT

/~~~

= 2_8 x IO ~ eXp

~~ ~ ~~~

m~

S~

RT

The standard deviations relative to these values are : 16 kJ mol~ for xi, II kJ mol~ I for x~, 20 kJ mol~ for x~ and 6 kJ mol~ for xe. In the x~

direction,

the

experimental points

do not lie on a

straight

line.

Nevertheless,

we think that it would be

interesting

to mention the mean

activation energy which is 144 kJ mol~

Supposing

a

single

average

jump mechanism,

the

value of the

pre-exponential

factor

Do,

is

probably

in the range

[10~

to I

m~

s~

Thus,

the

1.4

x10~m~s~l

value of

Do

related to this direction

probably

comes from an inexact

extrapolation

: within this range of temperatures, a

major

curvature of Arrhenius'

graph

exists.

The uncertainties of these values are rather

large.

These values could be

improved by enlarging

the range of temperatures. We think that it is

interesting

to

give

these values

(though they

do not have any immediate

physical meaning),

for two reasons : first

they

allow us to use an

approximate expression allowing

us to

predict by interpolation

or limited

extrapolation,

values

corresponding

to D at temperatures different from those of the

study second,

the

comparison

with other data

published

in the literature is

possible.

3.3 BULK SELF-DIFFUSION TENSORS IN NAPHTHALENE. The self-diffusion tensor is

easily

calculated from the self-diffusion coefficients measured in four different

crystallographic

directions. It expresses the

anisotropy

of the

phenomenon

in a mathematical way.

Ii Self-di#fizsion

tensor at 348 K : The

dita

relative

to 348

K, presented

in table II,

give

for the diffusion tensor referred to the reference axes

(0,

xi, x~, x~

(equivalent

to a

crystallographic

referential

(0,

a,

b, c*11

:

3.3 ° °.45

~ ~~-17 ~2

~- i

~

~~~~

~

~45 ~~ ~4 ~°'

~'

~'

~ *

The

principal

axes

Xi, X~

and

X~

of this tensor have been determined.

X~

is

parallel

to the symmetry axis b.

Xi

and

X~

are contained in the ac

plane,

and the

angle

q7

=

(a, Xi )

is found to be

equal

to 58°. With

respect

to the set of

principal

axes, the tensor is written as :

3.8±0.8 0 0

i~ ~ i

D

(348

K

)

= 0 2.9 ± 0.2 0 ~ ~~ ~ ~

0 0 2.9 ± 0.7

(°, '~1, '~2, '~3~

2) Self-di#fizsion

tensor at 343 K : from the data

presented

in table

III,

we obtain :

1.9

0 -0.45

i~ ~ i

D

(343 K)

= 0 2.6 0 ~

f~

~

0.45 0 2.4

~°'~' ~'

~

~'

(7)

a

'8

D,

ios T

338 T~KI

b

"

~~i'

~ '

2.85

m

~*

8

'

8

fl

Fig.

2. Variations of the bulk self-diffusion (o) and heterodiffusion coefficients (al with temperature in the a, b and c* directions. The continuous line represents the self-diffusion coefficient (S), the dotted

line the hererodiffusion coefficient (H).

(8)

Table II. Bulk

self-diffusion coejficients

at 338 K in

naphthalene.

Crystal

Diffusion D

Dx;

direction time in h in 10-17 m2 s-I in 10-17 m2 s-1

571 1.6 ± 0.I

xi 571 1.3 ± 0. I 1.5 ± 0.1

813 1.7 ± 0.1

720 1.3 ± 0.2

780 1.7 ± 0, I

x~ 730 1.8 ± 0. I 1.7 ± 0.1

730 1.4 ± 0.2

780 1.7 ± 0.1

814 0.7 ± 0.1

813 0.8 ± 0. I

x~ 720 0.5 ± 0,1 0.7 ± 0.1

720 1.0 ± 0.1

720 0.8 ± 0.1

800 1.6 ± 0. I

xe 723 1.8 ± 0. I 1.7 ± 0.1

723 1.9 ± 0.1

800 1.9 + 0.1

Table III. Bulk

self-diffusion coefficients

at 343 K in

naphthalene.

Crystal

Diffusion D

Dx;

direction time in h in 10-17 m2 s-I in 10-17 m2 s-1

484 1.3 ± 0. I

xi 329 1.6 ± 0.4 1.9 ± 0.2

329 2.4 ± 0.2

328 2.2 ± 0. I

x~ 220 2.2 ± 0.2 2.6 ± 0.1

220 2.8 ± 0.1

328 2.0 ± 0.4

x3 305 2.8 ± 0.1 2.4 ± 0.2

300 2.9 ± 0.2

xe 300 2.4 ± 0.2 2.6 ± 0.1

312 2.8 ± 0.1

360 2.8 ± 0.1

(9)

With q7

= 60°

2.7 ± 1.6 0 0

l~~

~ ,

D

(343 K)

= 0 2.6 ± 0.1 0 ~~ ~

0 0 1.6 ± 0.7

(°, '~1, X2, X3)

3) Self-dijfizsion

tensor at 338 K : from the data

presented

in table

IV,

we obtain :

1.5 0 0.60

li~

~ i

D

(338

K

)

= 0 1.7 0

(

~

f~

~

0.60 0 0.7 '

~'

'

~

~'

Table IV. Bulk

set-diffusion coefficients

at 348 K in

naphthalene.

Crystal

Diffusion D

Dx;

direction time in h in 10-17 m2 s-I in 10-17 m2 s-1

233 4.3 ± 0.2

xi 329 3.9 ± 0,1 3.3 ± 0.3

306 2.6 ± 0,1

234 2.5 ± 0.7

234 2.0±0.I

x~ 216 3.0±0.2 2.9±0.2

216 3.2±0.1

216 2.9±0.1

336 3.5 ± 0.I

x~ 259 3.0 ± 0.1 3.4 ± 0.2

330 3.8 ± 0.6

216 4.0 ± 0.4

xe 216 4.6 ± 0.1 3.8 ± 0.2

234 3.7 ± 0.2

234 3.6 ± 0.2

With q7

= 28°

1.8 ± 1.5 0 0

~~ ~

D

(338

K

= 0 2.6 ± 0.1 0 ~~ ~

0 0 0.4 ± 1.5

(0, Xi, X2, X3)

Figure

3

represents

the flux

ellipsoid,

in order to show the

preceeding

tensors. It

corresponds

to the

spatial

distribution of the flux of matter due to an

isotropic unitary

concentration

gradient.

The symmetry of the diffusion

phenomenon

is

clearly

indicated

by

these

ellipsoids,

the

binary

axis b of the structure

being

also one of the symmetry axes of the

ellipsoids.

The other two

symmetry

axes of the

ellipsoid, Xi

and X~ are contained in the ac

plane. They correspond

to the directions of the

highest

and lowest mobilities of

naphthalene

molecules in the

naphthalene crystal.

The fact that their directions are not

neighbouring

or confused with

significant

directions of the

crystalline

structure

description,

can be

explained by

the fact that

(10)

3

b

a

a

~

a

Fig.

3. Flux

ellipsoids

characteristic of the bulk sew-diffusion at 3 temperatures.

the observed effect is due to a

composition

of several directions of molecular

jumps,

which are

necessarily

linked to the

crystallographic

directions. These axes are more

easily

observed on sections of these flux

ellipsoids. Figure

4 shows the ac

plane

sections of these

ellipsoids,

which coincide with the extremities of the matter flux vectors when we

impose

an

isotropic unitary

concentration

gradient

of

spherical

symmetry. The

principal (or symmetrical)

directions of the resultant flux are

clearly

seen. The variation of these directions with temperature appears very small. The

tendency

to

isotropy

when T increases is

emphasized.

4.

Comparison

and discussion.

4,I SELF-DIFFUSION IN NAPHTHALENE SINGLE CRYSTAL. The

complete

measured self-

diffusion tensors in

naphthalene single crystals presented

in this paper are, to our

knowledge,

the first

published

in the literature. So

they

cannot be

compared

with other measurements of this

phenomenon. Nevertheless,

the self-diffusion coefficient in the c * direction was measured

by

Sherwood and White

[I]

in the temperature range 330-348 K. The variation with

temperature of their self-diffusion coefficient

obeys

an Arrhenius'law described

by

:

D

=

2.5 x lo ~~ exp

(-

~~~

~(f°~ m~

s~

In their

study, according

to this

equation,

at 343 K, D is

equal

to 14

x10~~~m~s~~.

Hampton

and Sherwood

[3]

have carried out the measurement of this coefficient on

crystals

of similar

quality,

in the c* direction.

They

obtained a value of lo x

10~l~ m~ s~~

within the

same

temperature

range. Their values are from 6 to lo times

higher

than ours. The influence of

(11)

,'X5(338K)

/ /

, /

', /

,

/

, a

,

/ /

,

/ ,

/

',J,(338K)

/ / /

,

Xi

(343K(~'~'~~~~~~

- corresponds to a flux of

lxlT17

molenfles

rn2s'I Fig.

4. Sections of the flux

ellipsoids by

the ac

plane.

impurities

on diffusion in this type of

crystals

was

emphasized by

Sherwood and White.

They

showed that

impurities considerably

increased the diffusion coefficients measured. Further-

more, these two teams have

probably

not well taken into account the influence of the extended

defects on the determination of the characteristic bulk self-diffusion coefficients

[14, 15].

Therefore,

we think that our values are

certainly

closer to the true intrinsic diffusion coefficients.

4.2 SELF-DIFFUSION AND HETERODIFFUSION OF 2-NAPHTHOL IN NAPHTHALENE. The Vari-

ation of

D~ (D~

is the heterodiffusion coefficient at infinite dilution of

2-naphthol

in

naphthalene)

with temperature in the studied range

[7]

can be

represented by

an Arrhenius law.

In table

V,

the

expressions

of the self-diffusion and heterodiffusion coefficients measured in Table V. Arrhenius

expressions

in bulk

heterodijfizsion

and

set-diffusion

in

naphthalene.

Crystal DH

in

In~

S

~~

'~

~~

~

d;rection 17] 1~

l

~ ~ ~~- 3 92 kJ mol~ I

~ ~ ~- 6 74 kJ mol~

~ ~ ~~~

RT ~ ~~~

RT

~ 97 kJ mol~ mo

2.3 x 10~ eXP

~~

$T

b I.I x IO eXP

RT

c*

4.0 x 10~ ~ exp ~~

$)°~

IA x

10~

exp ~~ " ~°~

RT

(12)

three directions xi, x~ and x~ are

given experimental points

are shown in

figure

2. The

influence of the limited

temperature

range

probably explains

the

dispersion

of the

Do

and AH~~' for the two

phenomena.

The same order of

magnitude

is

clearly

found for the two molecules in the same lattice. In the directions x~ and x~, it seems that the activation

enthalpies

are different. In the xi direction, the

experimental dispersion yields

the

equality

of the activation

enthalpies.

The

analysis

of these data carried out with a

single procedure

will allow

us to

distinguish

the

jump frequencies

of the two molecules. But the tensor of heterodiffusion is not yet known at the three temperatures.

In

figure 5,

the sections

by

ac and ah

planes

of the flux

ellipsoids

of self and heterodiffusion at 343 K are

given.

A great

similarity

appears. The

angle

between the

principal

axes is 21°.

C*

X31H343),

', /

', ,'

' /

' ,/ ,X31343K)

j , ,/

t

',

' II,

a

' /

/ ,

/ '

1'

"

/~

' "

,' '(i(H3431

- oo«esponds to a flux of W~17 molecules

m 2s'l

(I)

, ,

/ '

,'

"

1 '

/ ~H343

j j a

t ,

' /

I'

/

- oo«e~pontlsto aflux of

WT17

molecules

m

2f' (it)

Fig.

5. Sections of the self-diffusion and heterodiffusion flux

ellipsoids by

the ac and ab

planes

at

343 K : ac plane (ii, ab

plane

(iii.

(13)

This difference between the tensor orientation indicates a different contribution of the different molecular

jumps

in the two

phenomena.

But the common

crystalline medium,

and the

slight

difference between the molecular forms of

naphthol

and

naphthalene (see Fig. 6),

are the essential fact which is

clearly

seen in the tensor

similarity.

A further

interpretation

of these results will be

given

in the paper relative to the

microscopic

aspect of these mobilities.

~°~ f

,'

/

,~

/

(I)

(11)

Fig.

6. Chemical formulae for

2-naphthol

(ii and naphthalene molecules (iii.

5. Conclusion.

The most

important

result is the

description

of the obtention of a self-diffusion tensor in a monoclinic

crystal.

It seems to us that our self-diffusion coefficients are measured in

crystals

of

a better chemical and

crystalline quality

than those in Sherwood's

experiments.

The extension of the temperature range is necessary in order to obtain a more

precise frequency

factor and the activation

enthalpy. Nevertheless,

the

anisotropy

of self-diffusion in

naphthalene single crystals

is measured. It is not so

high,

and has a

tendency

to decrease when

temperature

increases. The

similitary

observed between the tensors measured at 343 K of self and heterodiffusion is an

interesting

result. It demonstrates the

important

part

played by

the

crystalline

structure of the host in the observed

anisotropies

of the mobilities of the two molecules.

References

[Ii SHERWOOD J. N., WHITE D. J., Philos. Mag. is (1967) 745.

[2] CORKE N. T., SHERWOOD J. N., J. Mat. Sci. 6 (1971) 68.

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Phys.

44 (1966) 4416.

[5] LEE C. N., REucRofT P. J., KEVORKIAN H. K., LABES M. M., J. Chem. Phys. 42 (1965) 1406.

[6] BONPUNT L., DAUTANT A., LOUMAID A. and FAURE F., J.

Phys.

Chem. Solids 50

(1989)

777-783.

[7] FAURE F., DAUTANT A., BENDANI A., BONPUNT L., J.

Phys.

Chem. Solids 51(1990) 1005-1010.

[8] LOUMAID A., Thbse Bordeaux 1 (1987).

[9] RAIMI K., Thbse Bordeaux 1 (1990).

[10]

KARL N.,

Crystal

Growth

Properties

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Applications (Springer,

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II ii BENDANI A., Thhe Bordeaux (1991).

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LECLAIRE A. D., RABINOVrrCH A., J.

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LECLAIRE A. D., RABINOVrrCII A., J.

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j14]

BONPUNT L., DAUTANT A., Theoretical and

Experimental

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Organic

Molecular Solids, Defect Control in Semi-conductors, Ed. K. Sumino, Elsevier Science

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1990),

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regus

au

de I et II

Weak

Superconductivity

A.

BARONE,

A.

LARKIN,

EdS.

Sdrie :

Progress

in

High Temperature Superconductivity,

vol. 4

(World Scientific, 1987)

ISBN :

9971-50-504-5,

407 pages,

52,

lo £.

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Naples

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JAW,

S. RADHAKRISHNA, EdS.

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Emerging Technology (World Scientific, 1987)

ISBN : 9971

50-531-2,

531 pages,

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£.

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M. V.

JARIC,

Ed.

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Order,

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HAUG,

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ISBN :

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D. C. LOOK

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chapitres

; introduction ; comportement

p6riodique simple birythmicit6

dans un mod~le

biochirnique

h deux variables; du comportement

p£riodique simple

aux oscillations

complexes

;

signaux

d'AMP

cyclique

chez les amibes

Dictostelium discodeum, oscillations

complexes,

mod~le

d'ontogen~se

des rythrnes

biologiques;

s6crdtions

p£riodiques

d'horrnones conclusions et

perspectives

;

bibliographie

et index.

Références

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