Experiments were carried out to grow 3.Nitroaniline (m.NA) crystals doped with 4.Nitroaniline (p.NA) and 2.chloro 4.Nitroaniline (CNA). The measured undercooling for m.NA, p.NA, and CNA were 0.21 tm K, 0.23 tm K, and 0.35 tm K respectively, where tm represents the melting temperature of the pure component. Because of the crystals' large heat of fusion and large undercooling, it was not possible to grow good quality crystals with low thermal gradients. In the conventional two-zone Bridgman furnace we had to raise the temperature of the hot zone above the decomposition temperature of CNA, p.NA, and m.NA to achieve the desired thermal gradient. To avoid decomposition, we used an unconventional Bridgman furnace. Two immiscible liquids, silicone oil and ethylene glycol, were used to build a special two-zone Bridgman furnace. A temperature gradient of 18 K/cm was achieved without exceeding the decomposition temperature of the crystal. The binary crystals, m.NA-p.NA and m.NA-CNA, were grown in centimeter size in this furnace. X-ray and optical characterization showed good optical quality

Henningsen, T.

Hopkins, R. H.

Mazelsky, R.

Singh, N. B.

English

NASA Technical Reports Server

NASA-TH-111073
GROWTH OF BINARY ORGANIC NLO CRYSTALS:
m.NA-p.NA and m.NA-CNA System
N. B. Singh, T. Henningsen, R. H. Hopkins, and R. Mazelsky
Westinghouse Science & Technology Center
Pittsburgh, PA 15235-5098
F. K. Hopkins
Materials Directorate, Wright Laboratory
WPAFB, OH 45433
D. O. Frazier
NASA George Marshall Space Flight Center
Huntsville, AL 35812
O.P.Singh
Chemistry Department, K.N.Government Post-Graduate College
Gyanpur, UP, India
ABSTRACT
Experiments were carried out to grow 3.Nitroaniline (m.NA) crystals doped
with 4.Nitroaniline (p.NA) and 2.chloro 4.Nitroaniline (CNA). The measured
undercooling for m.NA, p.NA, and CNA were 0.21 tm K, 0.23 tm K and 0.35 tm K
respectively, where tm represents the melting temperature of the pure component.
Because of the crystals' large heat of fusion and large undercooling, it was not possible to
grow good quality crystals with low thermal gradients, Ir.".!.-,-;: v ,i<:v ,uuorial two-zone
Bridgman furnace we had to raise the temperature of the hot zone above the
'(NASA-TM-111073) GROWTH OF BINARY N96-16014
ORGANIC NLO CRYSTALS: m.NA-p.NA AND
&,\s± m.NA-CNA SYSTEM (NASA. Marshall
*rt v*^ ^^V r+ — —- — f \ - L~ L. ** i _ _ » ^ f\I\^ Space Flight Center) 24 p Unclas
G3/76 0065422
https://ntrs.nasa.gov/search.jsp?R=19960008848 2020-06-16T06:00:10+00:00Z
decomposition temperature of CNA, p.NA, and m.NA to achieve the desired thermal
gradient. To avoid decomposition, we used an unconventional Bridgman furnace. Two
immiscible liquids, silicone oil and ethylene glycol, were used to build a special two-zone
Bridgman furnace. A temperature gradient of 18 K/cm temperature gradient was achieved
without exceeding the decomposition temperature of the crystal. The binary crystals,
m.NA-p.NA and m,NA-CNA, were grown in centimeter size in this furnace. X-ray and
optical characterization showed good optical quality.
1. BACKGROUND
Crystal growth techniques for inorganic optical materials from the melt were
developed in a relatively short span of time because a huge body of relevant literature was
available on the solidification of metals and alloys. The situation was very different for
the organic optical materials. Most of the crystal growth studies for organic materials
were based upon the model [1] to simulate the solidification behavior of high temperature
materials. Most of the metals and alloys freeze with a nonfacetted interface, which
involves a low heat of fusion during phase transformation. On the other hand, organic
materials which typically exhibit optical nonlinearities have high values of Afh/R and
grow with facets. Afh is the heat of fusion and R is the gas constant. Growth of this class
of materials is generally anisotropic and spikey, and materials generally need a high
degree of undercooling to initiate nucleation and to grow. Because these materials require
large undercooling, they often contain a large density of imperfections. For this situation,
a high thermal gradient is required to grow good quality crystals. We have extensively
studied [2,3] the purification, solidification behavior and crystal characteristics of pure
organic crystals. We also observed [4] that binary organics show higher optical
nonlinearities compared to parent components. But growth of binary organic 5 rcquinc
even higher thermal gradients to achieve good quality. The present study reports a novel
technique to achieve higher gradients by using two immiscible liquids. Crystals of the
m.NA-p.NA and m.NA-CNA systems were grown, and their optical quality was
evaluated.
2. EXPERIMENTAL METHODS
2.1 PURIFICATION OF SOURCE MATERIALS
The starting materials, m.NA, p.NA and CNA, were supplied with 99.0%
purity. m.NA and p.NA were then further purified by a combination of repeated
distillations followed by directional freezing in vacuum. The first and last part of the
frozen material was discarded since impurities tend to segregate to these regions. CNA
was purified by an evaporation method. Vacuum-sealed as-supplied material was placed
in a two zone furnace, with the bottom zone of the furnace at a higher temperature than the
top zone. The temperature of the bottom zone was raised close to the melting temperature
of CNA to achieve a good rate of evaporation.
2.2 HEAT OF FUSION MEASUREMENT
The heat of fusion of purified material was measured by Perkin Elmer DSC,
with computer-aided data acquisition analysis. Samples were prepared in hermetically
sealed aluminum pans. All runs were carried out in the range of 2 meal/sec, with a chart
speed of 5 mm/min, and with a chart range of 10 mV. The heating range was 1.5 K/min.
2.3 UNDERCOOLING MEASUREMENT
The undercooling measurements were carried out in a manner described in
reference 5.
2.4 THE CRYSTAL GROWTH FURNACE AND GROWTH OF CRYSTALS
We designed a two-zone Bridgman furnace employing silicone oil and ethylene
glycol as the heat transfer media. These liquids do not mix and maintain sharp phase
boundaries, with the silicon oil in the hot zone and the ethylene glycol in the cold zone.
The temperature of the hot zone was controlled to within 0.5K. The desired translation
rate of the furnace was maintained with a motor-driven gear.
Optical Characterization
The boules were grown in the form of a cylinder, 11 mm in diameter and 30 mm
long. Crystals were cut with a string saw, and crystals were fabricated with their polished
surfaces parallel to the cleavage plane. The bulk transparency was examined to identify
~v
the gross defects such as precipitates, bands and cracks in the crystals. The transmittance
of both crystals was measured in the range of 0.25 to 3.0 micrometer using a Varian
Model 2300 photospectronieter. X-ray Laue patterns were taken to identify the growth
orientations and evaluate the crystallinity of the crystals.
3. RESULTS AND DISCUSSION
The purification techniques for m.NA, p.NA and CNA are limited due to
contamination of these compounds with air and partial decomposition of these compounds
above their melting temperatures. The distilled material was directionally solidified in a
sealed evacuated quartz tube to avoid contamination. Yet, the partial decomposition at a
temperature above melting (150° C) created pyrolysis. Black particles and side products
were embodied in the directionally frozen material as shown in Figure 1. However, it was
found that the pyrolysis could be suppressed by working at lower temperatures.
The measured values of heat of fusion for m.NA, CNA and p.NA are listed in
Table 1. This shows that A^h/R is larger than 2, and these compounds belong to facetted
classes. Their solidification behavior will differ from metals and alloys because of the
high heat transfer during the solidification. The measured undercooling for m.NA, p.NA,
and CNA were 0.21 tm K, 0.23 ten K, and 0.35 tm K respectively, where ten represents the
melting temperature of the pure component. This observation was typical of materials
with a large heat of fusion which have a tendency to undercool significantly below the
melting point. Because of the large heat of fusion and the large undercooling, it was not
possible to grow good quality crystals at a low thermal gradients. In the conventional
two-zone Bridgman furnace, we had to raise the temperature of the hot zone above the
decomposition temperature of CNA, p.NA, and m.NA to achieve the desired thermal
gradient. To avoid the decomposition, we used an unconventional Bridgman furnace.
Two immiscible liquids, silicone oil and ethylene glycol, were used to build a special two-
zone Bridgman furnace. Figure 2 shows the temperature distributions of the same furnace
without and with the silicone oil/ethylene glycol as the heat transfer medium at the
identical controller setting. A temperature gradient of 18 K/cm was achieved without
exceeding the decomposition temperature of the crystal.
The phase-diagram for m.NA-p.NA for the low concentration region of p.NA is
shown in Figure 3. The dotted line shows the ideal curve predicted [4] from the physical
parameters. The phase-diagram is in good agreement with that predicted by Ozawa and
Matsuoka [3] for this system. The solid-liquid equilibrium data on this system along with
m.NA-CNA system [4] showed that p.NA or CNA will segregate in the liquid during the
directional solidification. Because of this reason, we used a low doping concentration
(less than 5 wt %) of CNA and p.NA in this study. Due to the large value of Afh/R,
crystals froze with a high heat transfer, and morphology was always facetted. To facilitate
the nucleation, we used a 3-centimeter long capillary attached to the main body of the
growth tube. In the case of the m.NA-CNA system, we also carried out several growth
runs with a preoriented seed. The growth speed was 0.7 to 1.0 cm/day.
When we used the capillary to grow m.NA-p.NA and m.NA-CNA crystals, the
cvyst?1; grew in the c-direction and the cleavage plane was the b-plane which is identical
to pure m.NA. The X-ray Laue patterns were much better on the cleavage plane and as
grown surfaces. Surfaces etched with acetone-water or alcohol-water mixtures did not
produce good quality surfaces. The pure m.NA crystal has a stronger tendency to cleave
and has more river pattern structure than doped m.NA crystals. The transparency of
m.NA-p.NA and m.NA-CNA crystals is shown in Figures 4 and 5 with and without a wire
mesh. Both crystals were free from gross defects such as microprecipitates, microcracks
and voids. We did not observe any optical distortion in the mesh image indicating good
crystal quality. The transmission curves for the m.NA-CNA and rn.NA-p.NA crystals are
shown in Figure 6. The transmission curve for the m.NA-CNA crystal showed only
characteristics bands. We did not observe any absorption bands due to residual impurities.
The m.NA-p.NA crystal showed continuous improvement in the transmission between 0.5
to 0.85 micrometer wavelength region (Figure 6). Also, the m.NA-p.NA crystal showed
several absorption bands in this region due to residual impurities. The comparison of both
transmission curves suggests that with the improved purification procedures, it should be
possible to produce m.NA-p.NA crystals free of absorption bands in the visible and near-
infrared regions.
A second harmonic conversion experiment was carried out for the CNA-m.NA
crystals. A Q-switched YAG laser operating at 1.06 micrometer with a pulse length of 10
ns was used to investigate the frequency doubling (SHG) and to evaluate the crystal
quality. The details of SHG measurements and results for m.NA-CNA crystals are given
in n ference 4 T: -• -yaality of beam converting to green light is shown in Figure 7.
Figure 7(a) shows significant scattering around the central beam. This scattering of light
is due to inhomogeneity in the refractive indices of the m.NA-CNA crystal. The beam
conversion with better optical quality crystal is shown in Figure 7(b). This shows a more
concentrated beam of light with less scattering due to better optical homogeneity. This
type of test for m.NA-p.NA crystal is still in progress.
10
4. SUMMARY
Single crystals of doped m.nitroaniline were grown by a modified Bridgman
growth method. Silicone oil and ethylene glycon were used to achieve the desired high
thermal gradient without raising the temperature of the hot zone above the decomposition
temperature of nitroanilines. The combination of source material purification and of a
thermal gradient of 18 K/cm produced good quality m.NA-CNA and m.NA-p.NA
crystals. Binary crystals showed less cleaving tendency compared to pure m.NA crystals.
The crystal of m.NA-p.NA showed absorption bands between 0.5 and 0.85 micrometer
wavelength region due to residual impurities.
ACKNOWLEDGEMENTS
We are thankful to the Materials Directorate, Wright Laboratory, Wright-
Patterson, AFB, Ohio, for the financial support under contract No. F33615-88-C-5506.
We thank NASA, George Marshall Space Center for the partial support to prepare the
cartridges of m.NA-p.NA system through purchase order H-20124, DCN 2-3-10-34841.
11
5. REFERENCES
1. N. B. Singh and M. E. Glicksman, J. Crystal Growth 98 (1989) 534.
2. N. B. Singh, R. H. Hopkins, R. Mazelsky, N. Singh, and D. Lemmon, J. Crystal
Growth 106 (1990) 106.
3. N. B. Singh, R. H. Hopkins, R. Mazelsky, R. N. Singh, N. Singh, and O. P. Singh,
Thermo. Chim. Acta 159 (1990) 297.
4. N. B. Singh, T. Henningsen, R. H. Hopkins, R. Mazelsky, R. D. Hamacher,
E. P. Supertzi, F. K. Hopkins, D. E. Zelmon, and O. P. Singh, J. Crystal Growth 128
(1993) 976.
5. R. P. Rastogi, N. B. Singh, and N. B. Singh, J. Crystal Growth 37 (1977) 329.
12
CAPTIONS FOR FIGURES
Figure 1 (a) m.NA-CNA crystal with impurity particles embodied in the bulk,
(b) m.NA-CNA crystal with relatively few impurity particles in the bulk.
Figure 2 Temperature distribution of the furnace (a) without and (b) with the heat
transfer liquids. (Circle, triangle, and square denotes different sets of
measurements.)
Figure 3 Partial phase-diagram for m.NA-p.NA system.
Figure 4 Bulk transparency of m.NA-p.NA crystal (a) with and (b) without wire mesh.
Figure 5 Bulk transparency of m.NA-CNA crystal (a) with and (b) without wire mesh.
Figure 6 Transmission curves for (a) m.NA-p.NA and (b) m.NA-CNA crystals.
Figure 7 SHG experiment through a (a) crystal which shows large scattering and
(b) crystal with good optical quality.
13
Table 1
Properties of m.NA, p.NA and CNA
Properties m.NA p.NA CNA
Chemical formula
Heat of fusion (cal/g)
Crystal system
Lattice parameter (A)
41.6
biaxial
a = 6.485
b = 19.306
c = 5.087
Z = 4
36.4
Orthorhombic Monoclinic
a = 12.347
b = 5.997
c = 8.583
Z = 4
14
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Growth of binary organic NLO crystals: m.NA-p.NA and m.NA-CNA system

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