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Gel growth and perfection of orthorhombic potassium perchlorate single crystals
Journal of Crystal Growth 47(1979) 213—218 © North-Holland Publishing Company
GEL GROWTH AND PERFECTION OF ORTHORHOMBIC POTASSIUM PERCHLORATE SINGLE CRYSTALS A.R. PATEL and A. VENKATESWARA RAO Department of Physics, Sardar Patel University, Vallabh Vidyanagar 388 120, Gujarat State, India Received 29 August 1978; manuscript received in final form 19 February 1979
The present paper describes detailed studies made on the growth and perfection of potassium perchlorate (KCIO
4) single crystals. Studies of various reactants on the growth of these crystals have been discussed. The advantages and disadvantages of djfferent acid set gels to grow these crystals have also been discussed. It has been shown that in test tube experiments, perchioric acid set gels are better, whereas in a beaker—single tube system, organic acid set gels yield better results than the mineral acid set gels. The effect of temperature on nucleation, growth and morphology of these crystals has been studied. It has been found that the nucleation density decreases as the temperature increases. A mixture of 36N H2S04 and O.25M Na2SO3 in the volume ratio 1 1 has been found to reveal as grown as well as freshly introduced dislocations in these crystals.
I. Introduction
mine the best experimental conditions leading to the growth of large and well formed single crystals, four different sets of test tube experiments were performed by adding different feed solutions either over HC1O4 set gels or by adding solutions of HC1O4 (or NaC1O4 or KC1) over KC1 (or NaClO4 or HC1O4) incorporated acetic acid gels. Experiments were also performed to grow the crystals in the above mentioned acid set gels (except HC1O4) using the beaker— single tube system [5]. Experiments were conducted at ambient temperature (25 to 30°C)unless otherwise stated. The effect of temperature on nucleation and growth of the crystals (using perchloric acid set gels and KC1 as feed solution) was studied in the range 20—50°C. The perfection of the crystals grown was studied by chemical etching technique. A mixture of 36N H2S04 and 0.25M Na2SO3 in the volume ratio 1: 1 has been used to reveal dislocations in these crystals. The crystals were etched for about 2 to 3 mm, rinsed in either, and dried. The etch patterns were then examined under a metallurgical microscope. The crystals were also etched after indenting with a diamond indentor. Analytical reagent grade chemicals and doubly distilled water were used throughout this study. In the test tube experiments the crystals grew up to 6 X
Single crystals of potassium perchlorate have been difficult to produce in a suitable size and quality for use in IR, ESR, EPR and ionic conductivity studies [1—4]. A few attempts to grow these crystals in gels were made in the past [5—7] and little effort was made to give data regarding their growth using reactants inside and above the gel, using various acid set gels, at different temperatures, and perfection. The present paper describes the results of the studies made on the growth and perfection of these crystals.
2. Experimental details The crystallization apparatus used in the present work consisted of test tubes of 2.5 cm diameter and 20 cm length, and a beaker—single tube system with a 250 ml beaker and a 2.2 cm diameter glass tube open at both ends. The chemical reactions taking place in the gel media for the formation of crystals were the same as reported previously [5]. Silica gels were prepared by mixing pure sodium silicate (sp.gr. 1.03) and different amounts of various acids: HC1, HNO3, H2S04, HC1O4, and acetic, propionic, citric and tartaric acid. In order to deter213
AR. Pate!, A. Venkateswara Rao / Gel growth and perfection of KC1O
214
4
3 in 15 days while in the beaker—single tube 5 X 4 mm system they grew up to 15 X 12 X 8 mm3 in about 70 days. The results reported here are based on the statistical average of five sets of experiments,
3. Results and discussion 3.1. Crystal growth in test tubes It is observed that the nucleation density is less and the size of the crytals grown is slightly bigger in KC1 incorporated gels, when NaC1O4 is used as feed solution instead of HC1O4. This may be due to the decrease in the pH of the gels in tubes with HC1O4 as feed solution. Hydrochloric acid formed by the reaction of KC1 with HCIO4, reduces the pH of the gel and thus increases the nucleation density. The nucleation centers occur more in NaCLO4 incorporated gels with KC1 as feed solution than in KC1 incorporated gels with NaC1O4 as feed solution, which is due to a slighter decrease in the pH of the gels by adding NaC1O4 to sodium silicate than when KCI is added. The results are shown in figs. la—ld. In HC1O4 set gels, the number density is less, the
~
—
~*
..‘— •‘~t. 4~
a
~., ..
b
size is bigger and comparatively more number of crystals are transparent than in other acid set gels. Out of various amounts and concentrations of HCIO 4 used to form good gel media and KC1 as feed solution, a combination of 10 ml of 1 N HC1O4 and 20 ml of sodium silicate to form a gel and 30 ml of 1 N KC1 as feed solution has been found to be the best in terms of crystal size, intercrystalline separation and clarity of the gel media. It has been found that the average crystal growth rate is the greatest near the top of the diffusion column where the concentration gradients are high, and small near the bottom where the gradients are small [5]. Corresponding to different growth rates, the dislocation density is also different, as shown in figs. 2a and 2b. Fig. 3 shows a plot of dislocation density versus depth of the crystals from below the gel—solution interface. 3.2. Crystal growth in beaker—single tube system In this method, acetic and propionic acid set gels have been found to be the best to grow KC1O4 crystals. The crystals growing in acetic acid set gel are shown in fig. 4. In the case of mineral acid set gels, the gels are
~
j
— •
.—
—.
* ...
.~ ,.
c
.-‘
— —
—
,~
S
d
Fig. 1. Crystals growing in test tubes with the solutions inside and above the gel, respectively: (a) KC1 and HCIO4 (b) NaClO4 and KC1; (c) KCI and NaClO4 (d) HC1O4 and KCI.
A.R. Pate!, A. Venkateswara Rao / Gelgrowth and perfection of KC1O
4
Fig. 2. Density of dislocations in crystals grown at two different depths (d) from gel—solution interface; (a) d 25mm (X11O).
setting either immediately or after ten days. With organic acids, gels can be set within the required time. That is, the range of the gel setting period is larger in the case of organic acid set gels than with mineral acid set gels. Moreover, in the case of mineral acid set gels, the pH changes rapidly compared to the organic acid set gels with an increase or decrease of a few ml
8 16 24 32 d(m) Fig. 3. Dislocation density (N) versus depth (d) from below gel—solution interface.
215
=
15 mm; (b) d =
______________________________________ ______
Fig. 4. Crystals growing in acetic acid set gel.
AR. Patel, A. Venkateswara Rao / Gel growth and perfection of KCIO
216
4
of acid (fig. 5). The pH values of other mineral, tartaric and acetic acid gel solutions are similar to HC1, citric and propionic acd gel solutions, respectively. In the case of organic acids, for the same pH value, a larger amount of acid is needed than with mineral acids, so that the organic acid set gels are less dense and more transparent than the mineral acid set gels.
N
140
100
60
3.3 Effect of temperature The variation in temperature showed that at constant K+ and ClO~ion concentration, more crystals nucleate at lower than at higher temperatures. Fig. 6 shows a plot of nucleation density versus temperature. The decrease in nucleation density at higher temperatures is due to the fact that an increase in temperature increases the aqueous solubiity of KC1O4 (fig. 7). In most of the cases, at 37°C, only two to three crystals were formed. But their growth ceased after six to seven days. By decreasing the temperature from 37 to 25°Cat a rate of 0.1°C/h, the growth rates and hence the size increased, which must be due to the gradual increase in supersaturation by lowering the temperature. It is observed that there is a remarkable change in the habit of crystals when the temperature changes. As the temperature increases, the growth rates along the [010] direction increase and along the [001] direction decrease. The
~
ib
~ pH Fig. 5. Variation of gel pH with different amount (A) of iN HU, iN citric acid and iN propionic acid: (.) HC1; (A) C6H807 (.) CH3CH2COOH.
20
2u
_______________________________ 25 30 35 T(°C)
Fig. 6. Nucleation density (TV) versus crystallization temperature (7):
(A)
iN KCI;(.) 1.SN KCI.
crystals grown at higher temperatures are slightly smaller compared to those grown at lower temperatures. 3.4. Etching The etch pits produced on {001} cleavage faces of KC1O4 by the mixture of 36N H2S04 and 0.25M Na2 SO3 in the volume ratio 1 : I, after etching for 3 mm, are shown in figs. 2a and 2b. It is essential to establish the reliability of a particular etchant for revealing dislocations on a crystallographic plane before using it for dislocation studies in a particular material. A
______________
20 30 40 50 T(°C) Fig. 7. Solubiity (S) of KC1O4 in aqueous solution versus temperature (7’).
AR. Pate!. A. Venkateswara Rao / Gelgrowth and perfection of KCZO
4
217
Fig. 8. Fich pits on the matched ~OUl} cleavage faces of KCIO4 (Xl 1W.
one-to-one correspondence the isetchgenerally pits on the opposite halves of between a cleavage
_____
considered as an adequate proof of the reliability of an etchant for revealing dislocations This has been observed in KC1O4 crystals, as evidenced from figs. 8a and 8b of matched {001} cleavage faces. The pits are elongated hexagonal shaped with elongation along [010]. The pits have also been found to grow bigger and deeper on successive etching, indicating thereby that they do mark the intersections of linear defects with {001} surfaces. The etchant mentioned above is also capable of revealing freshly introduced dislocations, as is evident from the rosette pattern around an indentation mark on the {001} face, as shown in fig. 9. It is observed that the average density of dislocations in gel grown KC1O4 single crystals varies from 2 2X 102 to 7X 10~cm
• ~.. ~
-
_____
_____
4 Conclusions 1’
_____
•
•
:.
•
Fig. 9. Rosette pattern around an indentation mark on
For the preparation of single crystals of KC1O 3 in size, suitable for IR,ESR,EPR,iomc 4 up to 120 mm conductivity and optical absorption spectroscopy
{ool} cleavage face of KCIO 4 (x 135).
measurements, growth in test tubes has several
218
AR. Pate!, A. Venkateswara Rao / Gel growth and perfection of KC1O
advantages over the beaker—single tube system, which requires relatively larger quantities of gels as well as feed solutions and more time. However, for beaker— crystals 3, the use of the up to or more than is500suggested. mm single tube system In test tube experiments, the density of the nucleation centres is much higher and the size of the crystals is much smaller in the gels mixed with KC1 or NaClO 4, than in the gels mixed with HC1O4. In beaker—single tube experiments, acetic or propionic acids set gels with 2N KC1 in the beaker and 0.5N NaC1O4 in the tube, as the reactants produce the best results. An increase in temperature reduces the number of nucleation centres.
Acknowledgements The authors are pleased to acknowledge much valued discussions with Dr. G.K. Shivakumar and Mr.
4
M.D. Mahajan during the course of the present work. We also wish to thank the UGC, New Delhi, India for financial support to one of us (A.V.R.). References
[1] N. Krishnamurthy, Proc. Indian Acad. Sci. A61 (1965)
118. [2] J.R. Byberg, S.J.K. Jensen and L.T. Muus, J. Chem. Phys. 46 (1967) 131. [3] J.C. Fayet, B. Thieblemont and C. Pariset, Compt. Rend.
(Paris) B268 (1969) 177.
[4] J.N. Maycock and V.R.P. Vemeker, Phys. Status Solidi 44 (1971) 97. [5] A.R. Patel and A. Venkateswara Rao, J. Crystal Growth 37 (1977) 288. [6] A.R. Patel and A. Venkateswara Rao, J. Crystal Growth 43(1978)351. [7] A.R. Patel and A. Venkateswara Rao, Indian J. Pure Appi. Phys. 16 (1978) 544.
GEL GROWTH AND PERFECTION OF ORTHORHOMBIC POTASSIUM PERCHLORATE SINGLE CRYSTALS A.R. PATEL and A. VENKATESWARA RAO Department of Physics, Sardar Patel University, Vallabh Vidyanagar 388 120, Gujarat State, India Received 29 August 1978; manuscript received in final form 19 February 1979
The present paper describes detailed studies made on the growth and perfection of potassium perchlorate (KCIO
4) single crystals. Studies of various reactants on the growth of these crystals have been discussed. The advantages and disadvantages of djfferent acid set gels to grow these crystals have also been discussed. It has been shown that in test tube experiments, perchioric acid set gels are better, whereas in a beaker—single tube system, organic acid set gels yield better results than the mineral acid set gels. The effect of temperature on nucleation, growth and morphology of these crystals has been studied. It has been found that the nucleation density decreases as the temperature increases. A mixture of 36N H2S04 and O.25M Na2SO3 in the volume ratio 1 1 has been found to reveal as grown as well as freshly introduced dislocations in these crystals.
I. Introduction
mine the best experimental conditions leading to the growth of large and well formed single crystals, four different sets of test tube experiments were performed by adding different feed solutions either over HC1O4 set gels or by adding solutions of HC1O4 (or NaC1O4 or KC1) over KC1 (or NaClO4 or HC1O4) incorporated acetic acid gels. Experiments were also performed to grow the crystals in the above mentioned acid set gels (except HC1O4) using the beaker— single tube system [5]. Experiments were conducted at ambient temperature (25 to 30°C)unless otherwise stated. The effect of temperature on nucleation and growth of the crystals (using perchloric acid set gels and KC1 as feed solution) was studied in the range 20—50°C. The perfection of the crystals grown was studied by chemical etching technique. A mixture of 36N H2S04 and 0.25M Na2SO3 in the volume ratio 1: 1 has been used to reveal dislocations in these crystals. The crystals were etched for about 2 to 3 mm, rinsed in either, and dried. The etch patterns were then examined under a metallurgical microscope. The crystals were also etched after indenting with a diamond indentor. Analytical reagent grade chemicals and doubly distilled water were used throughout this study. In the test tube experiments the crystals grew up to 6 X
Single crystals of potassium perchlorate have been difficult to produce in a suitable size and quality for use in IR, ESR, EPR and ionic conductivity studies [1—4]. A few attempts to grow these crystals in gels were made in the past [5—7] and little effort was made to give data regarding their growth using reactants inside and above the gel, using various acid set gels, at different temperatures, and perfection. The present paper describes the results of the studies made on the growth and perfection of these crystals.
2. Experimental details The crystallization apparatus used in the present work consisted of test tubes of 2.5 cm diameter and 20 cm length, and a beaker—single tube system with a 250 ml beaker and a 2.2 cm diameter glass tube open at both ends. The chemical reactions taking place in the gel media for the formation of crystals were the same as reported previously [5]. Silica gels were prepared by mixing pure sodium silicate (sp.gr. 1.03) and different amounts of various acids: HC1, HNO3, H2S04, HC1O4, and acetic, propionic, citric and tartaric acid. In order to deter213
AR. Pate!, A. Venkateswara Rao / Gel growth and perfection of KC1O
214
4
3 in 15 days while in the beaker—single tube 5 X 4 mm system they grew up to 15 X 12 X 8 mm3 in about 70 days. The results reported here are based on the statistical average of five sets of experiments,
3. Results and discussion 3.1. Crystal growth in test tubes It is observed that the nucleation density is less and the size of the crytals grown is slightly bigger in KC1 incorporated gels, when NaC1O4 is used as feed solution instead of HC1O4. This may be due to the decrease in the pH of the gels in tubes with HC1O4 as feed solution. Hydrochloric acid formed by the reaction of KC1 with HCIO4, reduces the pH of the gel and thus increases the nucleation density. The nucleation centers occur more in NaCLO4 incorporated gels with KC1 as feed solution than in KC1 incorporated gels with NaC1O4 as feed solution, which is due to a slighter decrease in the pH of the gels by adding NaC1O4 to sodium silicate than when KCI is added. The results are shown in figs. la—ld. In HC1O4 set gels, the number density is less, the
~
—
~*
..‘— •‘~t. 4~
a
~., ..
b
size is bigger and comparatively more number of crystals are transparent than in other acid set gels. Out of various amounts and concentrations of HCIO 4 used to form good gel media and KC1 as feed solution, a combination of 10 ml of 1 N HC1O4 and 20 ml of sodium silicate to form a gel and 30 ml of 1 N KC1 as feed solution has been found to be the best in terms of crystal size, intercrystalline separation and clarity of the gel media. It has been found that the average crystal growth rate is the greatest near the top of the diffusion column where the concentration gradients are high, and small near the bottom where the gradients are small [5]. Corresponding to different growth rates, the dislocation density is also different, as shown in figs. 2a and 2b. Fig. 3 shows a plot of dislocation density versus depth of the crystals from below the gel—solution interface. 3.2. Crystal growth in beaker—single tube system In this method, acetic and propionic acid set gels have been found to be the best to grow KC1O4 crystals. The crystals growing in acetic acid set gel are shown in fig. 4. In the case of mineral acid set gels, the gels are
~
j
— •
.—
—.
* ...
.~ ,.
c
.-‘
— —
—
,~
S
d
Fig. 1. Crystals growing in test tubes with the solutions inside and above the gel, respectively: (a) KC1 and HCIO4 (b) NaClO4 and KC1; (c) KCI and NaClO4 (d) HC1O4 and KCI.
A.R. Pate!, A. Venkateswara Rao / Gelgrowth and perfection of KC1O
4
Fig. 2. Density of dislocations in crystals grown at two different depths (d) from gel—solution interface; (a) d 25mm (X11O).
setting either immediately or after ten days. With organic acids, gels can be set within the required time. That is, the range of the gel setting period is larger in the case of organic acid set gels than with mineral acid set gels. Moreover, in the case of mineral acid set gels, the pH changes rapidly compared to the organic acid set gels with an increase or decrease of a few ml
8 16 24 32 d(m) Fig. 3. Dislocation density (N) versus depth (d) from below gel—solution interface.
215
=
15 mm; (b) d =
______________________________________ ______
Fig. 4. Crystals growing in acetic acid set gel.
AR. Patel, A. Venkateswara Rao / Gel growth and perfection of KCIO
216
4
of acid (fig. 5). The pH values of other mineral, tartaric and acetic acid gel solutions are similar to HC1, citric and propionic acd gel solutions, respectively. In the case of organic acids, for the same pH value, a larger amount of acid is needed than with mineral acids, so that the organic acid set gels are less dense and more transparent than the mineral acid set gels.
N
140
100
60
3.3 Effect of temperature The variation in temperature showed that at constant K+ and ClO~ion concentration, more crystals nucleate at lower than at higher temperatures. Fig. 6 shows a plot of nucleation density versus temperature. The decrease in nucleation density at higher temperatures is due to the fact that an increase in temperature increases the aqueous solubiity of KC1O4 (fig. 7). In most of the cases, at 37°C, only two to three crystals were formed. But their growth ceased after six to seven days. By decreasing the temperature from 37 to 25°Cat a rate of 0.1°C/h, the growth rates and hence the size increased, which must be due to the gradual increase in supersaturation by lowering the temperature. It is observed that there is a remarkable change in the habit of crystals when the temperature changes. As the temperature increases, the growth rates along the [010] direction increase and along the [001] direction decrease. The
~
ib
~ pH Fig. 5. Variation of gel pH with different amount (A) of iN HU, iN citric acid and iN propionic acid: (.) HC1; (A) C6H807 (.) CH3CH2COOH.
20
2u
_______________________________ 25 30 35 T(°C)
Fig. 6. Nucleation density (TV) versus crystallization temperature (7):
(A)
iN KCI;(.) 1.SN KCI.
crystals grown at higher temperatures are slightly smaller compared to those grown at lower temperatures. 3.4. Etching The etch pits produced on {001} cleavage faces of KC1O4 by the mixture of 36N H2S04 and 0.25M Na2 SO3 in the volume ratio 1 : I, after etching for 3 mm, are shown in figs. 2a and 2b. It is essential to establish the reliability of a particular etchant for revealing dislocations on a crystallographic plane before using it for dislocation studies in a particular material. A
______________
20 30 40 50 T(°C) Fig. 7. Solubiity (S) of KC1O4 in aqueous solution versus temperature (7’).
AR. Pate!. A. Venkateswara Rao / Gelgrowth and perfection of KCZO
4
217
Fig. 8. Fich pits on the matched ~OUl} cleavage faces of KCIO4 (Xl 1W.
one-to-one correspondence the isetchgenerally pits on the opposite halves of between a cleavage
_____
considered as an adequate proof of the reliability of an etchant for revealing dislocations This has been observed in KC1O4 crystals, as evidenced from figs. 8a and 8b of matched {001} cleavage faces. The pits are elongated hexagonal shaped with elongation along [010]. The pits have also been found to grow bigger and deeper on successive etching, indicating thereby that they do mark the intersections of linear defects with {001} surfaces. The etchant mentioned above is also capable of revealing freshly introduced dislocations, as is evident from the rosette pattern around an indentation mark on the {001} face, as shown in fig. 9. It is observed that the average density of dislocations in gel grown KC1O4 single crystals varies from 2 2X 102 to 7X 10~cm
• ~.. ~
-
_____
_____
4 Conclusions 1’
_____
•
•
:.
•
Fig. 9. Rosette pattern around an indentation mark on
For the preparation of single crystals of KC1O 3 in size, suitable for IR,ESR,EPR,iomc 4 up to 120 mm conductivity and optical absorption spectroscopy
{ool} cleavage face of KCIO 4 (x 135).
measurements, growth in test tubes has several
218
AR. Pate!, A. Venkateswara Rao / Gel growth and perfection of KC1O
advantages over the beaker—single tube system, which requires relatively larger quantities of gels as well as feed solutions and more time. However, for beaker— crystals 3, the use of the up to or more than is500suggested. mm single tube system In test tube experiments, the density of the nucleation centres is much higher and the size of the crystals is much smaller in the gels mixed with KC1 or NaClO 4, than in the gels mixed with HC1O4. In beaker—single tube experiments, acetic or propionic acids set gels with 2N KC1 in the beaker and 0.5N NaC1O4 in the tube, as the reactants produce the best results. An increase in temperature reduces the number of nucleation centres.
Acknowledgements The authors are pleased to acknowledge much valued discussions with Dr. G.K. Shivakumar and Mr.
4
M.D. Mahajan during the course of the present work. We also wish to thank the UGC, New Delhi, India for financial support to one of us (A.V.R.). References
[1] N. Krishnamurthy, Proc. Indian Acad. Sci. A61 (1965)
118. [2] J.R. Byberg, S.J.K. Jensen and L.T. Muus, J. Chem. Phys. 46 (1967) 131. [3] J.C. Fayet, B. Thieblemont and C. Pariset, Compt. Rend.
(Paris) B268 (1969) 177.
[4] J.N. Maycock and V.R.P. Vemeker, Phys. Status Solidi 44 (1971) 97. [5] A.R. Patel and A. Venkateswara Rao, J. Crystal Growth 37 (1977) 288. [6] A.R. Patel and A. Venkateswara Rao, J. Crystal Growth 43(1978)351. [7] A.R. Patel and A. Venkateswara Rao, Indian J. Pure Appi. Phys. 16 (1978) 544.