Materials Research Bulletin, Vol. 29, No. 3, pp. 309-316, 1994 Copyright © 1994 Elsevier Science Lid Printed in the USA. All rights reserved 0025-5408194$6.00+ ,oo
GROWTH AND CHARACTERIZATION OF PURE AND CADMIUM DOPED STRONTIUM TARTRATE TETRAHYDRATE SINGLE CRYSTALS
F.Jesu Rethinam, D.Arivuoli , S.Ramasamy and P.Ramasamy Department of Nuclear Physics, University of Madras, Madras-25 * Crystal Growth Centre, Anna University, Madras-25, INDIA. (Received
ABSTRACT The growth of pure and cadmium doped strontium tartrate tetrahydrate single crystals in silica gel is described. A systematic study of the dependence of the uptake of the dopant on the molarity of the dopant employed for the growth is presented in this paper. X-ray diffraction, Chemical etching, TGA, DSC, FTIR studies have been done and the results are reported. MATERIALS INDEX:
strontium and cadmium
Introduction The method of growing crystals in silica gel can be used for the preparation of doped crystals (I). Recently, the growth of doped crystals of calcium tartrate has drawn considerable amount of interest (2,3). Tartrates of calcium and strontium crystallize in the orthorhombic system with space group P212121 having four molecules in the unit cell (4-7) and the~ ~re found to be ferroelectric (8). This paper, to the best of our knowledge, reports for the first time, the results of a systematic study of the dependence of the uptake of the dopant in the crystal on the molarity of the dopant employed in the feed solution for growing the doped crystals. Experimental Formation of strontium tartrate tetrahydrate (STT) was accomplished by the reaction between SrCl^ and tartaric acid in sodium m e t a - s i l i c a t e gel. The experiments were carried out by the method of single test-tube diffusion, gel itself containing one of the reacting components i.e., tartaric acid. Here an aqueous_solution of sodium m e t a - s i l i c a t e gel 309
RETHINAM et al.
of density 1.05 g c m was i m p r e g n a t e d with the desired concentration of t a r t a r i c a c i d and set in test tubes of length 20 c m and d i a m e t e r 2.5 cm. 20 ml of a q u e o u s solution of SrCl 2 of d e s i r e d c o n c e n t r a t i o n was p o u r e d g e n t l y over the set gel along the sides of the tube. The supernatant solution was a l l o w e d to d i f f u s e into the gel medium. Pure STT c r y s t a l s a p p e a r e d w i t h i n two days at the gel-solution interface and within 4 days well below the i n t e r f a c e and the growth was continued for 45 days. For growing cadmium-doped STT crystals, 20 ml of a mixture of aqueous s o l u t i o n of IM SrCI^ and of CdCI~ of d~sired c o n c e n t r a t i o n was poured over the set gel and allowed to d i f f u s e into the gel. The experiments were carried out at the room t e m p e r a t u r e of 23 t 2 "C. Analytical Reagent grade chemicals and triple distilled water were employed throughout the experiment.
FIG.I M o r p h o l o g y of c a d m i u m - d o p e d strontium tartrate tetrahydrate c r y s t a l s (I d i v i s i o n = I mm)
and D i s c u s s i o n
The p u r e STT c r y s t a l s g r o w n at the interface showed dominant (001) face w i t h t r u n c a t e d (II0) and (011) faces. C r y s t a l s g r o w n b e l o w the i n t e r f a c e s h o w e d well d e f i n e d (110) face with (001) face at the edges. The crystals were c o l o u r l e s s 3 and transparent and their size varied from 3x2x0.5 m m to 12x7x5 m m . C o n c e n t r a t i o n p r o g r a m m i n g ( l ) was found to e n h a n c e the size (15x9x6 m m ) and t r a n s p a r e n c y of the crystals. In the case of doped crystals, as the c o n c e n t r a t i o n of CdCI 2 was d e c r e a s e d from 0.2M, the c r y s t a l s at the i n t e r f a c e s h o w e d well d e f i n e d (001) face. The d o p a n t had very little i n f l u e n c e on the d o m i n a t i n g (Ii0) face of the crystals growing b e l o w the interface. Crystals were found to n u c l e a t e and grow in the gel m e d i u m in the course of 6 days and t h e y w e r e c o l o u r l e s s . B e t t e r results in this cas~ w e r e o b t a i n e d (Fig.l) for a gel d e n s i t y of 1.05 g cm , pH 4.0, IM tartaric acid and IM SrCl for c o n c e n t r a t i o n s of CdCI 2 in the range 0 . 0 0 5 M to 0.2M.2It was observed that high c o n c e n t r a t i o n of the d o p a n t very much reduced the g r o w t h rate of the crystal. The effects of parameters such as gel density, and pH are summarized in Tabl~s 1 and 2. The n u c l e a t i o n d e n s i t y is m i n i m u m at 1.05 gcm
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Table 1 :
Effect of parameters on the growth of pure STT (When one parameter is varied and others are kept constant)
Variation in gel density (1.03, 1.04,1.05, 1.06)
Nucleation density is maximum at 1.03 and minimum at 1.05. Size of the crystal is maximum at 1.05 and minimum at 1.03
Variation in gel pH (3.4, 3.7, 4.0, 4.3)
Nucleation density maximum at 4.3 and minimum at 3.7. Size of the crystal is maximum at 3.4 and minimum at 4.3. As pH decreases, the depth of the first crystal arising in the gel column increases.
Variation in SrCl 2 concentration (0.5M, 1.0M, 1.5M)
Nucleation density minimum at 1.0M.
is maximum at 0.5M and
Variation in tartaric acid concentration (0.5M,0.75M, 1.0M)
Nucleation density minimum at 1.0M.
is maximum at 0.5M and
Effect of dopant concentration on the growth of cadmium doped crystals -3 (IM SrCl 2, IM tartaric acid, gel density 1.04 g c m , pH 4.0).
Concentration of CdC12
Size of the crystal 3 mm
0.2M O.1M O.05M O.01M O.O05M
EPD 3 -2 I0 cm
(2-2.5)xl.5xl (6-8)x(3-4)x3.0 (6-8)xf3-3.5)x2.5 (7-8.5)x(2.5-2.8)xl.8 (8.5-10.O)xl.3xl.0
22.3 16.5 12.1 3.74 2.5
Etch pit density increases as the concentration dopant increases and this is mainly due to distortion and hence the dislocation density.
Concentration the crystal
dependence of the uptake of was analyzed using atomic
of the lattice
the dopant absorption
F . J . RETHINAM et al.
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120C C 0
"o ..c 4.1
d C O O
Molority of the dopont in the supernotont solution FIG.2 C o n c e n t r a t i o n d e p e n d e n c e of the u p t a k e d o p a n t in the c r y t a l s
spectrophotometer. The results are shown in Fig.2. The FTIR results (Fig.3) along with the results of undoped crystalline sample are given in Table 3.
FIG.3 FTIR spectra of (a) undoped and (b) cadmium-doped sample
Z [.-. l--
Z .< me [.-
W A V E N U M B E R (CM -1 )
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Table 3 IR a s s i g n m e n t tartrate.
(a) u n d o p e d
(b) c a d m i u m
cadmium doped (0.1M) -i cm
-i cm 3851-2911(br)
water hydroxyl s t r e t c h C-H stretch
2362s 2339s 1577w
CJ°asymmetry o stretch
C~0 s y m m e t r y O stretch
O H - i n plane bend
1329w 1282m I146m I063s 1006m 930w 810w
1332w 1282m I147m i063s 1002m 931w 812w
C=O s t r e t c h
CH bend C-O(H)stretch C-C stretch OH o u t - o f - p l a n e bend CO2 d e f o r mation s: strong
The stretching v i b r a t i o n s of hydroxyl, w a t e r and CH g r o u p s give rise to a b s o r p t i o n b a n d s in the region 2 9 0 0 - 3 9 0 0 cm . A free t a r t r a t e ion has two hydroxyl groups. So two bands can be e x p e c t e d for the s t r e t c h i n g v i b r a t i o n of th~ hydroxyl group. A b r o a d band in the region 2 9 0 0 - 3 9 0 0 cm has been observed. T h i s is b e c a u s e of the reason that the bands due to s t r e t c h i n g v i b r a t i o n s of hydroxyl, w a t e r and CH groups are o v e r l a p p i n g and a p p e a r as broad ones. The inp l a n e and o u t - o f - p l a n e b e n d i n g m o d e s of the OH g r o u p and the d e f o r m a t i o n v i b r a t i o n s of CO 2 are also observed. The v i b r a t i o n a l m o d e s for C-OH, C-C groups have been assigned for the u n d o p e d and c a d m i u m - d o p e d samples. From the Table it is noted that t h e s e vibrational modes are unaffected in the u n d o p e d and in the doped crystalline
RETHINAM et al.
samples. Two bands have been observed for CO 2 symmetric stretching mode indicating the existence of carboxylate ions in the crystal (9). These vibrational modes of carboxyl group frequencies are assigned in the present study. A shift or modification is observed for these vibrational modes. This indicates the effect of the dopant. T~o strong new bands are also observed at 2362 and 2339 cm in the doped crystalline sample (Fig.3). The appearance of these new bands in the FTIR spectrum of the cadmium-doped specimens characterizes new chemical bonds. A similar effect was observed in the case of gel-grown doped crystals of AgSeO 4 (i0). From the TGA studies (Fig.4) it is quite clear that the crystals are hydrated. Mass loss calculation for different
74 ° ~
Temperature (c) FIG.4 TGA curve of the doped sample stages of decomposition clearly indicates that the crystal has four water molecules. This is in confirmation with Xray diffraction analysis. The DSC analysis (Fig. 5) in conjunction with TGA clearly indicates water of crystallization. The envelope (50-170"C) which includes the first and the second endothermic peaks in the DSC curve indicates the presence of adsorbed water as well as water of crystallization. The third and fourth endothermic peaks between 250"C and 320"C in the DSC curve may be due to splitting of one water molecule from the tartrate and complete removal of water of crystallization. (These two stages of DSC curve appear as a single stage in the TGA curve between 250°C and 320"C). The fifth endothermic peak after 410"C may be due to splitting of C^H20 from the remaining fragment. Thermal studies showed ~hat the doped
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crystals were crystals.
Temperature (C) FIG.5
DSC curve of the doped sample
D >. b,.
o cxJ -~0 tO
~°J 04 O4~T
2 8 (degree) FIG.6
X-ray powder diffractogram of the doped sample
R E T H I N A M e t al.
X-ray diffraction studies showed that the undoped crystals were orthorhombic with space group P2~2.2. and cell dimensions a=0.9510(I), b=I.0929 (4)and c=0.94~61(~)nm (8). Fig.6 is the powder pattern of the doped sample taken using powder diffractometer with CuKe radiation. Conclusions Growing crystals by employing concentration programming is found to enhance the size and transparency of the gel grown crystals. The doped crystals are found to be thermally more stable than the pure crystals. High concentration of the dopant very much reduces the growth rate of the crystals. The etch pit density increases with dopant concentration due to lattice distortion. The FTIR spectrum of the doped crystal indicates the formation of new chemical bonds due to the dopant. Acknowledgment One of the authors (F.J.R.) is grateful to UGC (India) for awarding the research fellowship and to Professor T.Nagarajan, Head, Department of Nuclear Physics, University of Madras for constant encouragement and support. We thank Dr.V.Sreedharan, Department of Nuclear Physics for his helpful discussion and Mr.B.Soundarajan for technical assistance . References i.
H.K.Henisch, Crystal Growth in Gels and Liesegang RingsCambridge University Press, 1986. 2. Ishihara and Nobukazu, Kenkyu kiyo - Nihon Daigaku Bunrigakubu Shizen Kagaku Kenkyusho., 25, 916(1990)(Japan) 3. G.Sperka and M.Bettinelli, Inorganica Chimica Acta., 149 147(1988) 4. F.C.Hawthorne, I.Borys and R.B.Ferguson, Acta Crystallogr.,B38, 2461(1982) 5. J.Bohandy and J.C.Murphy, Acta Crystallogr., B24, 286(1968) 6. Nakatani Noriyuki, Japan J.AppI. Phys. Part 2., 20(Iib), L1961 - L 1963 (Eng.)(1991) 7. F.Jesu Rethinam, D. Arivuoli, S. Ramasamy and P. Ramasamy, Cryst. Res. Technol., 28 (1993) 861. 8. H.B.Gon, J.Cryst. Growth., 102(3), 501(1990) 9. N.B.Colthup, L.H.Daly and S.E.Wiberlay, Introduction to Infrared and Raman S p e c t r o s c o p y . , New York and London, Academic Press (1964) 10. N.Dishovsky and Z.Boncheva-Mladenova, J.Cryst. Growth., 51 147(1981)