- Email: [email protected]
Growth and stability of pure and amino doped TGS crystals
Materials Chemistry and Physics 50 (1997) 233–237
Growth and stability of pure and amino doped TGS crystals S. Aravazhi, R. Jayavel, C. Subramanian U Crystal Growth Centre, Anna University, Madras 600 025, India Received 7 October 1996; revised 20 March 1997; accepted 20 March 1997
Abstract Pure and amino (L-alanine and L-valine) doped TGS crystals were grown by the slow cooling method. The rates of nucleation as indicated by the induction period were measured. Effects of dopants on the solubility, stability and induction periods were investigated in stirred solutions. The interfacial energy for pure and doped solutions at 308C was calculated. High quality single crystals of dimension 9=5=4 cm3 were grown. q 1997 Elsevier Science S.A. Keywords: Amino acids; Triglycine sulphate; Nucleation and growth
1. Introduction Triglycine sulphate (NH2CH2COOH)3PH2SO4 crystals are very important because of their application as room temperature (up to 498C) IR detectors and imaging systems. The crystal structure of TGS was reported by Hoshino et al. [1]. In the ferroelectric phase the Curie temperature Tc is approximately 498C and the symmetry is monoclinic with space group P21. Above the Curie temperature the structure gains an additional set of mirror planes in the space group P21/m. ˚ ; bs12.64 A ˚ ; cs The lattice parameters are as9.41 A ˚ ; bs1108239. Among the presently known pyroelec5.73 A trics, this class of materials has the highest pyroelectric coupling factor. These crystals are cleavable perpendicular to the ferroelectric b-axis. In triglycine sulphate, glycine itself is one of the amino acids. The substitution of another amino acid—alanine—in the place of glycine has been found to improve the crystal properties by contributing to effective internal bias in these crystals which, in turn, inhibits ferroelectric switching giving a permanently poled single domain crystal. This improves the device characteristics and hence alanine mixed crystals of the TGS family have been investigated by many researchers [2–9]. The spontaneous polarization of a ferroelectric crystal originates from the dipole moment of each dipole within the crystal. Some molecules with high dipole moments can be introduced into the polar lattice of a TGS crystal in such a way that their polar orienU
Corresponding author: e-mail: [email protected]
tation tends to coincide with that of bulk polarization. Thus, the pyroelectric properties of the crystal can be improved. The addition of organic dopants enhances the pyroelectric figure of merit which is an essential parameter for device application. For the fabrication of IR detectors and imaging systems, large size TGS crystals of wide b-plane are required, for which studies on fundamental growth parameters such as the solubility, metastable zone width and the induction period are very essential. Many authors have investigated the solubility of pure and doped TGS [10–12] and there is a wide variation in the values given by different investigators. However, reports on the basic growth parameters such as the metastable zone width and induction period are very scarce. Wang et al. [13] have studied the solution status of TGS and TGSP crystals. In the present study, an investigation was made on the basic growth parameters such as solubility, metastable zone width and the induction period for pure and amino doped TGS saturated solutions. After preparing the supersaturated solutions there is often a period where no phase change can be observed, known as the induction period; then minute nuclei appear and grow into visible crystals. The interfacial energy for pure and doped solutions at 308C was calculated. The presence of impurities affects the solubility, stability and the induction period. The aim of the present work is primarily to grow good quality bulk crystals of TGS for IR detectors and imaging applications and to examine the basic growth parameters of TGS solutions doped with L-alanine and Lvaline.
0254-0584/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved PII S 0 2 5 4 - 0 5 8 4 ( 9 7 ) 0 1 9 3 9 - 1
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
234
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
2. Experimental details
2.1. Solubility of pure and amino doped TGS solutions
Recrystallized salt was used to study the solubility of pure and amino doped (L-alanine, L-valine) for three different temperatures, namely 35, 40 and 458C. A sealed container charged with water and the solute, maintained at a constant temperature, was used to determine the equilibrium concentration. The solution was stirred continuously for 24 h. The content of the solution was analysed gravimetrically. The results are presented in Fig. 1.
2.2. Growth of pure and amino doped TGS crystals TGS was synthesized by taking analar grade glycine (CH2NH2COOH) and concentrated sulphuric acid (H2SO4). Glycine and sulphuric acid were taken in the ratio 3:1. The required volume of concentrated sulphuric acid was diluted with millipore water. Then the calculated amount of glycine salt was slowly dissolved in the diluted sulphuric acid. This solution was heated until the salt crystallized. Extreme care was taken while crystallizing the salt to avoid oxidation of glycine; the solution temperature was always maintained below 608C. The crystallized salt was again dissolved in millipore water and then recrystallized. In this way, the impurity content of TGS was minimized. Glycine reacts with sulphuric acid as follows: 3(NH2CH2COOH)qH2SO4™(NH2CH2COOH)3PH2SO4 The solution was filtered using a 0.2 mm porosity nuclear filter after suitable preheating. This solution was maintained at 608C for 2 days prior to loading into the crystallizer. The slow cooling method was adopted for the growth of crystals. An optically heated constant temperature bath of controlling accuracy "0.018C was used to perform the growth experiments. (001) seeds were employed for the growth of bulk pure TGS crystals. The temperature reduction was programmable at a rate of 0.03–0.38C/day during the initial and final stages of the growth run. The solution was thoroughly stirred at a constant speed both clockwise and anticlockwise so as to ensure that the concentration of the solution was kept constant throughout the growth experiment. The growth of amino doped TGS crystals was similar to that of pure TGS crystals except that as-grown seeds were employed in this case. 2.3. Metastable zone width and induction period measurements A 100 ml glass beaker was used as a nucleation cell. The nucleation cell was placed in a cryostat and the temperature
Fig. 1. Powder X-ray diffraction patterns of (a) pure TGS, (b) L-alanine doped TGS and (c) L-valine dopted TGS.
Fig. 2. Solubility of pure and amino doped TGS crystals as a function of temperature.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
235
was thermostatically controlled to an accuracy of "0.058C. The solution was stirred by means of a motor. A lamp placed at the rear of the cryostat was used to illuminate the nucleation cells. Recrystallized salt of TGS and millipore water was used in the present study. The dopants AR grade L-alanine and Lvaline were used to study their effect on the solubility, stability and induction period in the TGS saturated solutions at different temperatures. Aqueous solutions of pure and doped TGS were prepared by dissolving the required amount of TGS salt in 100 ml of millipore water at a temperature slightly higher than their respective saturation temperatures. The solution was continuously stirred for at least 24 h before use. The stability of the solutions was evaluated by means of the traditional polythermal measurements of the metastable zone. In the polythermal method [14], the solution is cooled from the overheating temperature until the first visible crystal appeared in the volume or at the bottom of the crystallizer. The induction periods of pure and doped solutions were measured by means of the isothermal method [14]. When the temperature reached the desired value, it was held constant, until the first crystal appeared was measured.
3. Results and discussion
Fig. 3. (a) Morphology of pure TGS crystal grown using as-grown seed; (b) Morphology of pure TGS crystal grown using (001) seed.
A bulk transparent TGS crystal of dimension 9=5=4 cm3 was harvested. Powder X-ray diffraction patterns for pure and doped TGS crystals are shown in Fig. 2. The unit cell dimensions were determined using an Enraf-Nonius FR 590 single crystal X-ray diffractometer. The results are given in Table 1. Fig. 3(a) shows the morphology of pure TGS crystal grown from the as-grown seed; this morphology is different from the crystal grown using a (001) seed (Fig. 3(b)).
Fig. 4. (a) Pure TGS crystal, (b) L-alanine doped TGS crystal and (c) L-valine doped TGS crystal.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
236
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
Fig. 5. Metastable zone width measurements for pure and doped TGS.
When a (001) seed was used the resulting crystal had a wide b-plane which is favourable for IR imaging applications. Fig. 4 shows the pure and amino doped TGS crystals. The doping of amino acids has a significant effect on the basic growth parameters. It is observed that the solubility decreases while doping. This is in accordance with the common ion effect, where the growth process is accelerated by reducing the solubility. The metastable zone width measurements for pure and doped TGS solutions are presented in Fig. 5. The results are the average of three reproducible observations. The introduction of dopants in the TGS solution has enhanced the rate of formation of nuclei; this in turn has decreased the metastable zone width. Theories of homogeneous nucleation developed by Volmer and Weber [15], Becker and Doring [16] and Turnbull and Fisher [17] form the basis of the approach to nucleation studies [18]. According to the classical theory of homogeneous formation of spherical nuclei [15] 16pa3V 2NA ln tsyln Bq 3 3 3R T (ln S)2
(1)
where V is the molar crystal volume, NA is Avogadro’s number, R is the gas constant and S is the relative supersaturation. ln B depends weakly on temperature, so there is a linear dependence relation ln t and (ln S)y2 at constant T. As shown in Fig. 6, when ln t is plotted against (ln S)y2, the data give straight lines in accordance with Eq. (1). The interfacial energy values obtained from the slopes of these lines are in the range of 2–6 mJ my2 at 308C for both pure and amino doped TGS. It has been reported that the presence of soluble impurities reduces the solubility and hence decreases Table 1 Unit cell parameters of pure and doped TGS Samples
˚) a (A
˚) b (A
˚) c (A
b (8)
Pure TGS ATGS VTGS
5.7254 5.7457 5.7182
12.6445 12.6093 12.5823
9.1583 9.0897 9.1599
105.5318 105.3251 105.5351
Fig. 6. Plot of ln t against (ln S)y2: (a) pure TGS solutions; (b) L-alanine doped and (c) L-valine doped.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
the induction period [19]. This is in good agreement with our experimental results.
4. Conclusion The results obtained in the present work are the basis for the growth of bulk TGS crystals. It has been found from the experimental observations that the solubility, metastable zone width, induction period decrease with doping of amino acids. This is attributed to the increase in the rate of formation of nuclei while doping with amino acids and hence the role of dopants on the nucleation process has been studied. Using these optimized growth parameters, sizable crystals of amino doped TGS are grown. Electrical characterization studies on these crystals are in progress.
References [1] S. Hoshino, Y. Okaya and R. Pepinsky, Phys. Rev., 115 (1959) 323.
237
[2] C.S. Fang, Yao Xi, A.S. Bhalla and L.E. Cross, Ferroelectrics, 51 (1983) 669. [3] H. Ishida and K. Imai, Ferroelectrics, 106 (1990) 315. [4] J.E. Lorenzo, J.L. Martinez, C. Prieto and J.A. Gonzalo, Ferroelectrics, 81 (1988) 49. [5] F. Jimenez, B. Jimenez, S. Ramos and J. Del Cerro, Ferroelectrics, 79 (1988) 261. [6] T. Jasinki and J. Stavikowska, Ferroelectrics, 8 (1988) 99. [7] A.S. Bhalla, C.S. Fang, Y. Xi and L.E. Cross, Appl. Phys. Lett., 43 (1983) 932. [8] K.L. Bye, P.W. Whipps and E.T. Keve, Ferroelectrics, 4 (1972) 253. [9] V.A. Borinsenok, T.R. Volk, A.S. Koshelev, E.Z. Novitskii, S.A. Shramchenko and L.A. Shuvalov, Sov. Phys. Crystallogr., 33 (1988) 780. [10] R. Nitsche, Helv. Phys. Acta., 31 (1958) 306. [11] B. Brezina, Mater. Res., 6 (1971) 401. [12] R.J. Davey and E.A.D. White, J. Cryst. Growth, 30 (1975) 125. [13] O.W. Wang and C.S. Fang, Cryst. Res. Technol., 27 (2) (1992) 245. [14] N.P. Zaitseva, L.N. Rashkovich and S.V. Bagatyareva, J. Cryst. Growth., 148 (1995) 276. [15] M. Volmer and A. Weber, Z. Phys. Chem., 119 (1926) 277. [16] R. Becker and W. Doring, Ann. Phys., 24 (1935) 719. [17] D. Turnbull and J.C. Fisher, J. Chem. Phys., 17 (1949) 71. [18] J.W. Mullin and M.M. Osman, Krist. Tech., 8 (1973) 471. [19] S. Nagalingam, S. Vasudevan and P. Ramasamy, Cryst. Res. Technol., 16 (6) (1981) 647.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
Growth and stability of pure and amino doped TGS crystals S. Aravazhi, R. Jayavel, C. Subramanian U Crystal Growth Centre, Anna University, Madras 600 025, India Received 7 October 1996; revised 20 March 1997; accepted 20 March 1997
Abstract Pure and amino (L-alanine and L-valine) doped TGS crystals were grown by the slow cooling method. The rates of nucleation as indicated by the induction period were measured. Effects of dopants on the solubility, stability and induction periods were investigated in stirred solutions. The interfacial energy for pure and doped solutions at 308C was calculated. High quality single crystals of dimension 9=5=4 cm3 were grown. q 1997 Elsevier Science S.A. Keywords: Amino acids; Triglycine sulphate; Nucleation and growth
1. Introduction Triglycine sulphate (NH2CH2COOH)3PH2SO4 crystals are very important because of their application as room temperature (up to 498C) IR detectors and imaging systems. The crystal structure of TGS was reported by Hoshino et al. [1]. In the ferroelectric phase the Curie temperature Tc is approximately 498C and the symmetry is monoclinic with space group P21. Above the Curie temperature the structure gains an additional set of mirror planes in the space group P21/m. ˚ ; bs12.64 A ˚ ; cs The lattice parameters are as9.41 A ˚ ; bs1108239. Among the presently known pyroelec5.73 A trics, this class of materials has the highest pyroelectric coupling factor. These crystals are cleavable perpendicular to the ferroelectric b-axis. In triglycine sulphate, glycine itself is one of the amino acids. The substitution of another amino acid—alanine—in the place of glycine has been found to improve the crystal properties by contributing to effective internal bias in these crystals which, in turn, inhibits ferroelectric switching giving a permanently poled single domain crystal. This improves the device characteristics and hence alanine mixed crystals of the TGS family have been investigated by many researchers [2–9]. The spontaneous polarization of a ferroelectric crystal originates from the dipole moment of each dipole within the crystal. Some molecules with high dipole moments can be introduced into the polar lattice of a TGS crystal in such a way that their polar orienU
Corresponding author: e-mail: [email protected]
tation tends to coincide with that of bulk polarization. Thus, the pyroelectric properties of the crystal can be improved. The addition of organic dopants enhances the pyroelectric figure of merit which is an essential parameter for device application. For the fabrication of IR detectors and imaging systems, large size TGS crystals of wide b-plane are required, for which studies on fundamental growth parameters such as the solubility, metastable zone width and the induction period are very essential. Many authors have investigated the solubility of pure and doped TGS [10–12] and there is a wide variation in the values given by different investigators. However, reports on the basic growth parameters such as the metastable zone width and induction period are very scarce. Wang et al. [13] have studied the solution status of TGS and TGSP crystals. In the present study, an investigation was made on the basic growth parameters such as solubility, metastable zone width and the induction period for pure and amino doped TGS saturated solutions. After preparing the supersaturated solutions there is often a period where no phase change can be observed, known as the induction period; then minute nuclei appear and grow into visible crystals. The interfacial energy for pure and doped solutions at 308C was calculated. The presence of impurities affects the solubility, stability and the induction period. The aim of the present work is primarily to grow good quality bulk crystals of TGS for IR detectors and imaging applications and to examine the basic growth parameters of TGS solutions doped with L-alanine and Lvaline.
0254-0584/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved PII S 0 2 5 4 - 0 5 8 4 ( 9 7 ) 0 1 9 3 9 - 1
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
234
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
2. Experimental details
2.1. Solubility of pure and amino doped TGS solutions
Recrystallized salt was used to study the solubility of pure and amino doped (L-alanine, L-valine) for three different temperatures, namely 35, 40 and 458C. A sealed container charged with water and the solute, maintained at a constant temperature, was used to determine the equilibrium concentration. The solution was stirred continuously for 24 h. The content of the solution was analysed gravimetrically. The results are presented in Fig. 1.
2.2. Growth of pure and amino doped TGS crystals TGS was synthesized by taking analar grade glycine (CH2NH2COOH) and concentrated sulphuric acid (H2SO4). Glycine and sulphuric acid were taken in the ratio 3:1. The required volume of concentrated sulphuric acid was diluted with millipore water. Then the calculated amount of glycine salt was slowly dissolved in the diluted sulphuric acid. This solution was heated until the salt crystallized. Extreme care was taken while crystallizing the salt to avoid oxidation of glycine; the solution temperature was always maintained below 608C. The crystallized salt was again dissolved in millipore water and then recrystallized. In this way, the impurity content of TGS was minimized. Glycine reacts with sulphuric acid as follows: 3(NH2CH2COOH)qH2SO4™(NH2CH2COOH)3PH2SO4 The solution was filtered using a 0.2 mm porosity nuclear filter after suitable preheating. This solution was maintained at 608C for 2 days prior to loading into the crystallizer. The slow cooling method was adopted for the growth of crystals. An optically heated constant temperature bath of controlling accuracy "0.018C was used to perform the growth experiments. (001) seeds were employed for the growth of bulk pure TGS crystals. The temperature reduction was programmable at a rate of 0.03–0.38C/day during the initial and final stages of the growth run. The solution was thoroughly stirred at a constant speed both clockwise and anticlockwise so as to ensure that the concentration of the solution was kept constant throughout the growth experiment. The growth of amino doped TGS crystals was similar to that of pure TGS crystals except that as-grown seeds were employed in this case. 2.3. Metastable zone width and induction period measurements A 100 ml glass beaker was used as a nucleation cell. The nucleation cell was placed in a cryostat and the temperature
Fig. 1. Powder X-ray diffraction patterns of (a) pure TGS, (b) L-alanine doped TGS and (c) L-valine dopted TGS.
Fig. 2. Solubility of pure and amino doped TGS crystals as a function of temperature.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
235
was thermostatically controlled to an accuracy of "0.058C. The solution was stirred by means of a motor. A lamp placed at the rear of the cryostat was used to illuminate the nucleation cells. Recrystallized salt of TGS and millipore water was used in the present study. The dopants AR grade L-alanine and Lvaline were used to study their effect on the solubility, stability and induction period in the TGS saturated solutions at different temperatures. Aqueous solutions of pure and doped TGS were prepared by dissolving the required amount of TGS salt in 100 ml of millipore water at a temperature slightly higher than their respective saturation temperatures. The solution was continuously stirred for at least 24 h before use. The stability of the solutions was evaluated by means of the traditional polythermal measurements of the metastable zone. In the polythermal method [14], the solution is cooled from the overheating temperature until the first visible crystal appeared in the volume or at the bottom of the crystallizer. The induction periods of pure and doped solutions were measured by means of the isothermal method [14]. When the temperature reached the desired value, it was held constant, until the first crystal appeared was measured.
3. Results and discussion
Fig. 3. (a) Morphology of pure TGS crystal grown using as-grown seed; (b) Morphology of pure TGS crystal grown using (001) seed.
A bulk transparent TGS crystal of dimension 9=5=4 cm3 was harvested. Powder X-ray diffraction patterns for pure and doped TGS crystals are shown in Fig. 2. The unit cell dimensions were determined using an Enraf-Nonius FR 590 single crystal X-ray diffractometer. The results are given in Table 1. Fig. 3(a) shows the morphology of pure TGS crystal grown from the as-grown seed; this morphology is different from the crystal grown using a (001) seed (Fig. 3(b)).
Fig. 4. (a) Pure TGS crystal, (b) L-alanine doped TGS crystal and (c) L-valine doped TGS crystal.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
236
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
Fig. 5. Metastable zone width measurements for pure and doped TGS.
When a (001) seed was used the resulting crystal had a wide b-plane which is favourable for IR imaging applications. Fig. 4 shows the pure and amino doped TGS crystals. The doping of amino acids has a significant effect on the basic growth parameters. It is observed that the solubility decreases while doping. This is in accordance with the common ion effect, where the growth process is accelerated by reducing the solubility. The metastable zone width measurements for pure and doped TGS solutions are presented in Fig. 5. The results are the average of three reproducible observations. The introduction of dopants in the TGS solution has enhanced the rate of formation of nuclei; this in turn has decreased the metastable zone width. Theories of homogeneous nucleation developed by Volmer and Weber [15], Becker and Doring [16] and Turnbull and Fisher [17] form the basis of the approach to nucleation studies [18]. According to the classical theory of homogeneous formation of spherical nuclei [15] 16pa3V 2NA ln tsyln Bq 3 3 3R T (ln S)2
(1)
where V is the molar crystal volume, NA is Avogadro’s number, R is the gas constant and S is the relative supersaturation. ln B depends weakly on temperature, so there is a linear dependence relation ln t and (ln S)y2 at constant T. As shown in Fig. 6, when ln t is plotted against (ln S)y2, the data give straight lines in accordance with Eq. (1). The interfacial energy values obtained from the slopes of these lines are in the range of 2–6 mJ my2 at 308C for both pure and amino doped TGS. It has been reported that the presence of soluble impurities reduces the solubility and hence decreases Table 1 Unit cell parameters of pure and doped TGS Samples
˚) a (A
˚) b (A
˚) c (A
b (8)
Pure TGS ATGS VTGS
5.7254 5.7457 5.7182
12.6445 12.6093 12.5823
9.1583 9.0897 9.1599
105.5318 105.3251 105.5351
Fig. 6. Plot of ln t against (ln S)y2: (a) pure TGS solutions; (b) L-alanine doped and (c) L-valine doped.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991
S. Aravazhi et al. / Materials Chemistry and Physics 50 (1997) 233–237
the induction period [19]. This is in good agreement with our experimental results.
4. Conclusion The results obtained in the present work are the basis for the growth of bulk TGS crystals. It has been found from the experimental observations that the solubility, metastable zone width, induction period decrease with doping of amino acids. This is attributed to the increase in the rate of formation of nuclei while doping with amino acids and hence the role of dopants on the nucleation process has been studied. Using these optimized growth parameters, sizable crystals of amino doped TGS are grown. Electrical characterization studies on these crystals are in progress.
References [1] S. Hoshino, Y. Okaya and R. Pepinsky, Phys. Rev., 115 (1959) 323.
237
[2] C.S. Fang, Yao Xi, A.S. Bhalla and L.E. Cross, Ferroelectrics, 51 (1983) 669. [3] H. Ishida and K. Imai, Ferroelectrics, 106 (1990) 315. [4] J.E. Lorenzo, J.L. Martinez, C. Prieto and J.A. Gonzalo, Ferroelectrics, 81 (1988) 49. [5] F. Jimenez, B. Jimenez, S. Ramos and J. Del Cerro, Ferroelectrics, 79 (1988) 261. [6] T. Jasinki and J. Stavikowska, Ferroelectrics, 8 (1988) 99. [7] A.S. Bhalla, C.S. Fang, Y. Xi and L.E. Cross, Appl. Phys. Lett., 43 (1983) 932. [8] K.L. Bye, P.W. Whipps and E.T. Keve, Ferroelectrics, 4 (1972) 253. [9] V.A. Borinsenok, T.R. Volk, A.S. Koshelev, E.Z. Novitskii, S.A. Shramchenko and L.A. Shuvalov, Sov. Phys. Crystallogr., 33 (1988) 780. [10] R. Nitsche, Helv. Phys. Acta., 31 (1958) 306. [11] B. Brezina, Mater. Res., 6 (1971) 401. [12] R.J. Davey and E.A.D. White, J. Cryst. Growth, 30 (1975) 125. [13] O.W. Wang and C.S. Fang, Cryst. Res. Technol., 27 (2) (1992) 245. [14] N.P. Zaitseva, L.N. Rashkovich and S.V. Bagatyareva, J. Cryst. Growth., 148 (1995) 276. [15] M. Volmer and A. Weber, Z. Phys. Chem., 119 (1926) 277. [16] R. Becker and W. Doring, Ann. Phys., 24 (1935) 719. [17] D. Turnbull and J.C. Fisher, J. Chem. Phys., 17 (1949) 71. [18] J.W. Mullin and M.M. Osman, Krist. Tech., 8 (1973) 471. [19] S. Nagalingam, S. Vasudevan and P. Ramasamy, Cryst. Res. Technol., 16 (6) (1981) 647.
Journal: MAC (Materials Chemistry and Physics)
Article: 1991