GROWTH OF DOPED CRYSTALS

Transcription

1 CHAPTER4

2 GROWTH OF DOPED CRYSTALS

3 CONTENTS PAGE 4.1 Introduction Growth of Cobalt (II) doped crystlils Growth of Nickel (II) doped crystals Growth of Copper (II) doped crystals Growth of Cadmium (II) doped crystals Growth of Chromium (III) doped crystals Growth of Iron (III) doped crystals Morphology of doped crystals Conclusion 71 References 72

4 4.1 INTRODUCTION There are literally thousands of reports in the scientific literature concerning the effects of impurities on -the growth of specific crystals (1-3). Any substance other than the material being crystallized can be considered as an impurity. The presence or impurities in a system can have profound effects on the growth of a crystal and on its properties (4). The gel method of growing crystals can be used for the preparation of doped crystals and by this method the crystals can be doped more uniformly than in a free solution (5,6). Crystals can generally be doped by the use of small amounts of impurities, either in the outer reagent (supernatant solution) or in the gel itself. This chapter describes the growth of doped crystals of strontium, calcium and ammonium hydrogen d- tartrate in sodium metasilicate gel at rnom temperature. Cobalt (II), Nickel (II), Copper (II), Cadmium (II), Chromium (III) and Iron (III) has been used as the dopants. These dopants were employed as they have higher solubility in the host lattice compared to other possible dopants. 4.2 GROWTH OF COBALT (II) DOPED CRYSTALS Tartaric acid was titrated over the sodium metasilicate gel of the desired density. The titration continued until the contents attained the desired ph. The solution thus produced was transferred to straight tubes of diameter 2.5 cm and of length 20 cm. The gel solution was allowed to set in. After the gel was set firmly, a solution (supernatant solution) containing 1 M Calcium chloride or Strontium chloride or 2.5 M Ammonium bromide and 0.05 M cobalt (II) chloride was poured drop by

5 drop along the sides of the tube. The tube was sealed and left,undisturbed at room temperature. Slow diffusion of the upper reactants occurred through the gel, resulting in crystal growth. Crystals were found to nucleate and grow in gel medium in the course ofa week. Pink coloured crystals [Fig. 4.l(a), (b) & (c)] were found to grow well below the gel- solution interface and completion of crystallization took about 70 days. In order to investigate the growth conditions,' experiments were carried out for gel density in the range 1.03 to 1.06 gm/ ml, gel ph 3.0 to 6.0, concentration of the feed solution in the range 0.25 M to 2.0 Min the case of Calcium and Strontium and 1 M to 3 M for Ammonium and volume of the supernatant solution in the range 10 ml to 30 ml. However, the volume of the gel solution impregnated with tartaric acid was kept constant (50 ml). At lower densities of the gel solution, the population density was high and the grown crystals were extremely small, but transparent. At higher densities of the gel solution, the population density was low; the size of the crystal was large and the transparency poor. A density of 1.04 g/ml was found suitable for the growth of all the crystals. When the concentration of upper reactant was low, crystals were found to grow only at the gel-solution interface and when it was high, too many crystals were found to grow due to the spurious nucleation. A concentration 1 M. of Calcium and Strontium chlorides and 2.5 M of Ammonium bromide was found quite suitable to grow good crystals. Similarly a concentration of lm of tartaric acid and an aging of gel for 3 days were found suitable for Calcium and Strontium tartrate and a concentration of 2.5 M of tartaric acid and an aging of 18 days for ammonium 66

6 hydrogen d - tartrate crystals. Pink coloured crystals were found to grow only below at a distance of 1.5 cm from the gel- solution interface. A good number of them were found to grow at a distance about 1.5 cm to 3.5 cm from the gel-solution interface and beyond 4.5 cm their number was found to decrease with the distance from the interface. A few small crystals were also found to grow at the gel-solution interface and they were all found to be colourless. A molarity of 0.05 M, compared to other molarities, seemed suitable to obtain cobalt doped strontium tartrate crystals of considerable size, transparency and number. Pink coloured, well-defined, transparent crystals were found to grow well below the gel-solution interface. Their maximum size was approximately 7x 3 x 2.5 mm 3. For growing the other doped crystals, the same procedure, as for cobalt (II) doped crystals were adopted; replacing cobalt (11) chloride by the chloride of the respective dopant. For instance, to grow copper (11) doped tartratc crystals, cobalt (11) chloride was replaced by copper (II) chloride. Analytical reagent grade chemicals and triple distilled water were used throughout this study. The experiments were carried out at room temperature. 4.3 GROWTH OF NICKEL (II) DOPED TAR.TR.ATE CRYSTALS The optimized growth parameters for nickel-doped crystals were found to be the following; density of the gel solution 1.04 g/ml, ph value of the gel 4.0; molarity of strontium/ calcium chloride, 1 M, that of ammonium bromide 2.5 M; molarity of tartaric acid, 0.5 M for strontium and calcium, while for ammonium, the molarity of 67

7 tartaric acid is 2.5 Mand the volume of the supernatant solution, 20 ml (7) Yellowish green crystals of good transparency were found to grow for the molarity 0.01 M of nickel (II) chloride. Some of the grown crystals are shown in fig 4.2. For molarities higher than 0.1 M, some colourless clusters were found to grow at the interface in addition to a few light green crystals. A molarity of 0.01 M of nickel (II) chloride was found suitable to obtain nickel-doped crystals. Their, maximum size was approximately 7 x4 x3 mm 3 and they were yellowish green in colour. Fig 4.2 (a), (b) & (c) 4.4 GROWTH OF COPP:13:R (II) DOPED TARTRATE CRYSTALS Attempts to grow copper (II) doped tartrate crystals resulted in the growth of beautiful yellow coloured crystals with high morphological perfection. The optimized parameters for copper (II) doped crystals were found to be the following: density of the gel solution, 1.04 g /ml, ph value of the gel 4.0; molarity of strontium/ calcium chloride, 1 M; molaiity of tartaric acid 1 M; and volume of the supernatant solution, 20 ml. While for ammonium tartrate crystals, the molarity of tartaric,icid is 2.5 M and that of the ammonium bromide is also 2.5 M. Yellow coloured crystals were found to grow for the molarity 0.1 M of copper (II) chloride. Fig 4.3(a), (b) & (c) show some of the grown crystals. A molarity of 0.1 M was found to give crystals of good size and transparency. Their maximum size was approximately 8 x 3.5 x 2 mm 3. Concentration programming improved the size and transparency of the crystals.. 68

8 4.5 GROWTH OF CADMIUM (II) DOPED TARTRATE SINGLE CRYSTALS Among all the doped crystals grown in the present study, this particular dopant alone gave colourless crystals. The optimized growth parameters for cadmium (II) doped tartrate single crystals were found to the following; density of the gel sol11tio g/ml; ph value of the gel 4.0, molarity of tartaric acid 1 M, molarity or strontium chloride/ calcium chloride, l M; and volume of the supernatant solution 20 ml. While for ammonium tartrate crystals, the molarity of ammonium bromide and tartaric acid were 2.5 M. Colourkss lrnnspan.:nt crystals were fuu11d to grow wdl below Ilic gel solution interface. Good crystals of considerable size and transparency were obtained for the molarity 0.1 M. Their maximum size were 6 X 5X 3 mm 3. In this case the dendrites were found to grow only for the concentration M. Fig 4.4(a), (b) &(c) show some of the cadmium-doped crystals. 4.6 GROWTH OF CHROMIUM (Ill) DOPED TARTRATE SINGLE CRYTALS A comparatively less transparent dark green crystals (fig 4.5) were those harvested when an attempt was made to grow chromium (III) doped Strontium/ Calcium tartrate crystals. While in the case of Ammonium hydrogen d - tartrate, pale green transparent crystals (fig 4.6) were obtained. The optimized growth parameters were found to be the following, density of the gel solution, 1.04 g/ml; ph value of the gel, 4.0; molarity of tartaric acid, 1 M; molarity of strontium I calcium chloride, 1 M; dopant concentration, 0.0 I M; and volume of the supernatant solution, 20 ml. Tn the case of ammonium hydrogen d- tartrate single crystals, the molarity ul

9 the tartaric acid is 2.5 M and that of the ammonium bromide solution is also 2.5 M. Attempts to grow chi omiutn-cloped crystals revealed that good crystals could be obtained for the dopant concentration 0.0 l M. The maximum size of the eloped crystals was approximately 8 X 3 X 2.5 mm 3 Fig. 4.5 (a), (b) & (c). 4.7 GROWTH OF IRON (Ill) DOPED TARTRATE SINGLE CRYTALS Crystals with a colour that matches with that of gold (Yellow) were obtained while making attempts to grow iron (III) eloped crystals (fig 4.7). Yellow coloured crystals were obtained for the molarity O.OlM of fcn-ic chloride. The optimized growth parameters for iron (III) doped Calcium and Strontium tattrate were found to be the following: density of the gel solution, 1.04 g/ml; ph value of the gel, 4.0; molarity of Calcium and strontium chloride, lm; molarity of tartaric acid, 0.5 M and volume of the supernatant solution, 20 ml. In the case of ammonium hydrogen d tartrate single cryst.ils, the molarity of the tartaric acid is 2.5 M and that of the ammonium bromide solution is also 2.5 M. A molarity of 0.01 M of ferric chloride was found to be suitable for obtaining iron - doped crystals of considerable size and transparency. The maximum size of the crystals was found to be approximately 7 x 4 x 3 mm 3. Fig 4.6 (a), (b) & (c). In the case of d-aht crystals the size was larger than that of calcium and strontium crystals. 4.8 MORPHOLOGY OF DOPED CRYSTALS There are reports (8-10) in the literature regarding the effects of impurities on the habit of crystals, although many of them are qualitative only (4). All doped crystals were found to have the morphology as shown in fig (4,?(a)) with well- 70

10 developed prismatic and pyramidal faces; and the morphology shown in Figure (4.7(b)). In the case of chromium (III) and iron (III) doped crysta\s the prismatic faces were not well developed. 4.9 CONCLUSION A variety of doped crystals of Calcium tartrate, Strontium tartrate and Ammonium hydrogen d - tartrate single crystals have been grown with cobalt (II), Nickel (II), Copper (II), Cadmium (II). Chromium (III) and Iron (III) as the dopants. The growth procedure has been described, the optimum growth parameters for the growth of the crystals have been presented and the nature of the doped crystals has been studied. The doped crystals were found to be coloured, except in the case of cadmium. The colour, size, transparency and the population density of the doped crystals depend on the molarity of the chloride of the respective dopant in the supernatant solution The doped crystals, in general, had well-developed, prismatic and pyramidal faces.. But at higher molaritfos of the dopants, the pyramidal faces were found to be truncated. The morphology of the pure crystals was found to be totally absent in the case of all doped crystals. 71

11 Fig COB~[T DOPED TARTRATE CRYSTALS Fig.4.1 (a) Calcium tartrate Fig.4.1 (b) Strontium tartrate Fig.4.1 (c) Ammonium Hydrogen d-tar trate

12 Fig NICKEL DOPED TARTRATE CRYSTALS Fig.4.2 (a) Calcium tartrate Fig.4.2 (b) Strontium tartrate Fig.4.2 (c) Ammonium Hydrogen d-tartrate

13 Fig COPPER DOPED TARTRATE CRYSTALS Fig.4.3 (a) Calcium tartrate Fig.4.3 (b) Strontium tartrate Fig.4.3 (c) Ammonium Hydrogen d-tartrate

14 Fig CADMIUM DOPED TARTRATE CRYSTALS Fig.4.4 (a) Calcium tartrate Fig.4.4 (b) Strontium tartrate Fig.4.4 (c) Ammonium Hydrogen d-tar trate

15 Fig CHROMIUM DOPED TARTRATE CRYSTALS Fig.4.S (a) Calcium tartrate Fig.4.S (b) Strontium tartrate Fig.4.S (c) Ammonium Hydrogen d-tartrate

16 Fig IRON DOPED TARTRATE CRYSTALS Fig.4.6 (a) Calcium tartrate Fig.4.6 (b) Strontium tartrate Fig.4.6 (c) Ammonium Hydrogen d-tartrate

17 ( 11 0 ) ( 1\ 0) (a} ( 1 00) ( b) Fig Morphology of the doped crystals

18 REFERENCES 1. Khamskii E. V. 'Crystallization from solutions', Consultants, New York (1969) 2. Reid. R.C. ALCh.E.Jl., 13 (L967) Sears G.W. 'Growth and Perfection of Crystals', Symposium Proceeding&, Wiley, New York (1958) Mullin. J.W. 'Crystallization'. CRC Press, International Scientific Series, Cleveland, Ohio (1960). 5. Lefaucheux. F, Rober M.C t, Gits S, Berbard Y & Gauthier B. Manuel, Rev. Int. Hautcs. Temper. Refract. Fr., 23 (1986) Sahaya Shajan & Mahadevan. C Crys. Res. Technol., 40, No. 4, (2005), Jesu Rethinam F, Arivuoli D & Ramasamy S. Cryst. Res. Technol., 28 (1993) Michaels A. S& Colville. A.R. J. Phys. Chem., 64 (1960) 13. 9; Mullin J.W., Amatavivadhana A., Chakraborty M: J. Appl. Chem., 20.(197q) Sahaya Shajan & Mahadevan. C J. Mater.Sci.Lett., 39, (2004),