The importance of understanding the mechanisms associated with defect generation during growth and the influence of gravity is stressed. An experiment is described. The advantages of adapting this experiment to the FES are then discussed. A brief survey of the ground based research under way is given

Authier, A.

Lefaucheux, F.

Robert, M. C.

English

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CRYSTAL GROWTH BY PRECIPITATION UNDER MICROGRAVITY*
A.Authier, F. Lefaucheux, M.C. Robert
Laboratoire de Mineralogie Cristallographie
associe au CNRS, Universite P. et M. Curie, Paris,France
ABSTRACT
After having stressed the importance of understanding the mechanisms
associated with defect generation during growth and the influence of
gravity, the experiment planned for FSLP is described. The advantages
of adapting this experiment to the FES are then discussed. A brief sur-
vey of the ground based research under way is given.
* Supported in part by the Centre National d1 Etudes Spatial'es, France
147
https://ntrs.nasa.gov/search.jsp?R=19820024196 2020-03-21T06:21:50+00:00Z
CRYSTAL GROWTH BY PRECIPITATION UNDER MICROGRAVITY
A.Authier, F. Lefaucheux, M.C.Robert
Laboratoire de Mineralogie Cristallographie
Associe au CNRS,Universite P. et M. Curie, Paris, France
INTRODUCTION
The influence of growth defects on many physical properties is well
known. Semiconductors, piezoelectrical, electrooptical, LASER crystals are
good examples. It is therefore very important to learn how defects arise,
how to control them and thus how to produce higher quality crystals. These
crystals are grown by various methods, from the melt, from the solution or
from the vapour phase. The nature of the defects produced during growth
depends in general much more on which one of these growth techniques is
being used and how. far from thermal equilibrium growth is performed than
on the actual chemical nature of the crystal. This is particularly true
in the case we shall be dealing with in this paper, namely growth from the
solution. It is therefore better to perform these studies on model crystals
which are easiest and fastest to grow and are best fitted for the study of
defects and the derivation of general laws on the generation of defects.
It will of course be still better if these crystals have interesting
physical properties which could be tested in crystals with different crys-
talline perfection and on crystals grown on earth and under microgravity
conditions.
The major growth defects are growth bands and growth
striations, growth sector boundaries, inclusions and dislocations (1),(2).
Growth bands are many in nature, ranging from very thin defects nearly one
atomic layer in thickness to layers in inclusions and to periodic varia-
tions of the lattice parameter associated to corresponding variations in
impurity content or vacancy concentration. The origin of these defects is
usually attributed among other causes to convectional instabilities asso-
ciated to temperature gradients or to temperature fluctuations. The main
factor for these convection effects is gravity which correlates temperature
differences and mass transfers. The various parameters which govern the
growth processes and on which the origin of growth defects depends are
supersaturation, temperature, pressure, nature and velocity of the solu-
tion flux etc ... These parameters are not independent, in particular
precisely because of the presence of gravity. In order to understand the
influence of these various parameters on the generation of defects it
is necessary to be able to vary them independently. A good way to do that
is to perform the growth under microgravity conditions so that convection
effects should be considerably reduced.
148
PREVIOUS STUDIES ON THE RELATIONS BETWEEN
GROWTH DEFECTS AND GROWTH CONDITIONS
Many studies have been performed in our laboratory on the characte-
rization of growth defects and on the relations between growth conditions
and growth defects. These experiments have been carried out on calcite (3),
(4)(5), KDP and KDKP (6,(7), TGS (8), germanates (9), potash alum (10)(11).
The various types of growth defects which may arise were identified. In
many cases the relation between the growth rate of a face and the screw
character of dislocations intersecting this face was clearly demonstrated.
Different types of growth defects appear when a perturbation is voluntarily
introduced at a given type during growth. Depending on the intensity of
the perturbation it may be a very thin growth bane or a growth band decorated
with inclusions generating or not dislocation bundles. The influence of the
solution flux on the generation of defects was established. In particular,
it was shbwn that dislocations are formed on the side of the crystal facing
the flux and that liquid inclusions are trapped at the backside which stop
dislocation propagation. The development of these defects depends on the
values of the supersaturation and of the flux rate and the influence of
these parameters was systematically studied. The best quality crystals are
obtained when the crystal is stationary with respect to the solution.
DESIGN OF THE EXPERIMENT TO BE PERFORMED IN FSLP
In order to increase crystalline perfection convections should be
avoided and growth performed in a purely diffusional system. It can be
shown that growth rates would be extremely long:in that case (1?) unless a
concentration gradient is imposed in some way. One way is to create a
temperature gradient between the crystal seed and the solution as proposed
by R. LAL (13) for the FES. This may however be the sources of inner
stresses within the growing crystal. Another way is that used by D. LIND(14)
for the growth of crystals by coprecipitation from the solution in ASTP.
We had already used this technique for the study of the habit of calcite
crystals depending on the nature of impurities (15).
The principle of the experiment is as follows. Two solutions AB and
CD are contained in two compartments 1 and 2 separated by a third one
containing a neutral solution N. At the beginning of the experiment
compartments 1 and 2 are put in communication with the third one and the
solutions AB and CD are allowed to diffuse in it. When they meet, a
- 1 4 9 ' . - . - . - .
reaction takes place of the type ORIGINAL PAGE fS
OF POOR QUALTTY
AB + CD + BD
BD remains in the solution and AC which is very l i t t le soluble precipitates.
D. L I N O ' S set up in the fol lowing :
Figure 1
Two pistons are pulled back at the beginning of the experiments
thus putting compartments 1 and N, and 2 and N in communication.
In the experiment which we shall perform in FSLP, we shall use a
cell of a completely different design in a thermostat where the temperature
will be constant to * 0.1° C. In our design, compartments 1 , 2 and N
are concentric cylinders, 1 and 2 being annular and on the outside
and N an inner cylinder :
Figure 2
There are openings on the lateral side of the inner cylinder. Before
the experiment starts, they do not lie in front of the outer compartments
(fig. 2a). By translating the inner cylinder by means of a motor, the openings
can be brought in front of compartments 1 and 2 (fig. 2b). Solutions AB
and CD then diffuse in the inner compartment. Porous diaphragms on each
side of the central reactive cell ensure that the solution flow is laminar.
With this set up the compartments are put in communication at constant
volume. Furthermore, the movement of the cylinder during the opening will
be extremely slow (it will take about half an hour). For all these reasons
there will be minimum perturbation of the diffusion flow during the opening
process and afterwards. The dimensions of the cell have been determined after
calculating the diffusion profiles in order to optimize maximum growth during
the time alloted for the experiment (about 90 hours).
The crystals to be grown in the experiment are various phosphates
of divalent cations, in particular calcium and lead. They have been chosen \
on one hand because they grow fast (it is possible to obtain crystal plate-
lets one centimeter accross in a few days) and in a shape which allows
X-ray topographic studies of the as grown crystal without any cutting to
be required, and on the other because they have interesting properties,
either physical (lead phosphate is ferroelectric) or biological (calcium
phosphate). In the future, other phosphates such as aluminum or lanthanum
may also be considered because of their highly interesting physical proper-
ties. The type of chemical reaction which will be used will be, for ins-
tance in the case of brushite, of the type
Ca H POA, 2H90
NH4 H2 P04 +.Ca(No3)2 + * *; . ,,'
^ • • ' • • ' " • . ; " " ' • •
GROUND BASED EXPERIMENTS
 :
The present ground based research is carried out along two main
directions. One is concerned with hydrodynamic studies and calculation
of diffusion profiles. The other one is concerned with growth in purely
diffusional conditions. A good way to achieve this result on earth is to
use gel growth. We are using it for growing both brushite (16)(17) and
lead phosphate. It has been checked that purely diffusional conditions
have indeed been achieved in our experiments and that PICK's law applies
to a very good accuracy, whatever the diameter of the tubes used for the
151
gel growth or the diffusion lengths. Several'types of gels have been
tested, with different densities and pH and the crystalline perfection is
assessed in each ease by X-ray topography. High quality crystals 10x10x0.5mm
have thus been obtained.
Furthermore, ground tests on the cell to be flown in FSLP are under
way.
PROPOSED EXPERIMENT IN THE F.E.S.
The experimental set up available in the FES would allow us to
perform simultaneously two types of experiments. The first one would be
devoted to a continuous observation during the whole length of the expe-
riment of the following growth parameters by means of the holographic
system : solution flow and isoconcentration curves to be compared after-
wards to calculated ones according to the diffusion theory, nucleation,
position, number, growth rate and habit changes of the crystals, isoconcen-
tration gradients around each crystal etc ... On the other hand, it would
be extremely interesting to study the influence of a perturbation of the
growth conditions on the growth and the generation of defects. This has
already been shown in our earlier experiments and in a study by F.Mussard
and S. Goldsztaub (18) who have grown sodium chlorate crystals under an
interferometric optical microscope. They correlated local perturbations
of the concentration gradient observed optically to the generation of
dislocation bundles observed afterwards by X-ray topography and to a
corresponding dramatic increase of the growth velocity of the face inter-
sected by these dislocations. We therefore propose that the second expe-
riment which could be performed would be study of a perturbation of a
single growth parameter. The temperature would be maintained constant and
a perturbation in the flow of matter would be introduced at half the time
alloted to the experiment by traversing the inner cylinder respective to
the outer compartment in order to cut the communication between compart-
ments 1 and 2 and the neutral compartment and then to open it again.
By means of the holographic system the perturbation of the solution flow
and isoconcentration curves could be measured. X-ray topography of the
crystals performed afterwards in the laboratory would show whether defects
were generated due to the perturbation and of what nature.
152
CONCLUSIONS .
Microgravity provides unique conditions for the study of crystal
growth and the understanding of the generation of growth defects as well
as for the obtention of high perfection crystals. The facility available
in FES is very well suited for these types of studies since the hologra-
phic system will enable a continuous observation of the growth conditions
and any observed change can be correlated afterwards to the defects
observed in the crystals by X-ray topography.
REFERENCES
[I] A.Authier. J. Crystal Growth, 13/14, 34 (1972)
[2] A.Authier, Crystal Growth and Materials, p. 516, Ed. by E.Kaldis
and H.J. Scheel, North Holland (1977)
[3] F.Lefaucheux, M.C. Robert and A.Authier, J. Cryst. Growth, 19, 329
(1973) ~~
[4] N. Yu Ikornikova, F. Lefaucheux and M.C. Robert, High Temperatures,
High Pressures, 6, 635 (1974)
[5] F.Lefaucheux and M.C. Robert, J. Crystal Growth, 38, 29 (1977)
[6] C.Belouet, E. Ounia and J.F. P6troff, J. Cryst. Growth, j!3, 243 (1974)
[7] C.Belouet, M.Monnier, E. Dunia and J.F. PStroff, Mat. Res. Bull.,
JJ., 903 (1976)
[8] A.Izrael, J.F. Petroff, A. Authier and Z. Malek, J. Cryst. Growth,
16, 131 (1972)
[9] L.MDemianetz, N.G. Duderov, A.N. Lobachev, F. Lefaucheux, M.C.Robert
and A. Authier, J. Cryst. Growth, 44, 570 (1978)
[10] S. Gits-Leon, F.Lefaucheux et M.C. Robert, J. Cryst. Growth, 44,
345 (1978) ~
[II] S. Gits-Leon, M.C. Robert and A.Zarka, Bull.Miner., JjOU 399 (1978)
[12] B.Simon, J. Cryst. Growth, 43, 640 (1978)
[13] R. Lai, NASA Technical Memorandum TM 78214 p.25 (1978)
[14] M.D. Lind, A.S.T.P. Preliminary Report, NASA TM X-58173, p.30-1,(1978)
[15] F. Lefaucheux, Bull. Soc. fr. Miner. Crist., 94, 2 (1971)
[16] F. Lefaucheux, M.C. Robert, H. Arend, J. Cryst. Growth, 47 (1979)
[17] F. Lefaucheux, M.C. Robert, E. Manghi, H. Arend, Poster session
ECCG 2, Lancaster 1979
[18] F. Mussard and S. GOLDSZTAUB, J. Cryst. Growth, 13/14. 445 (1972)
153


Crystal growth by precipitation under microgravity

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