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Growth and dielectric properties of l -arginine acetate and l -arginine oxalate single crystals
Materials Letters 62 (2008) 3742–3744
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Growth and dielectric properties of L-arginine acetate and L-arginine oxalate single crystals M. Meena, C.K. Mahadevan ⁎ Physics Research Centre, S.T. Hindu College, Nagercoil — 629 002, Tamilnadu, India
A R T I C L E
I N F O
Article history: Received 22 February 2008 Accepted 10 April 2008 Available online 16 April 2008 Keywords: l-arginine acetate l-arginine oxalate Crystal growth Dielectric properties
A B S T R A C T Single crystals of L-arginine acetate (LAA) and L-arginine oxalate (LAO), potential nonlinear optical materials, have been grown from respective aqueous solutions by using the slow cooling method. X-ray diffraction measurements confirmed the material of the grown crystals. Dielectric measurements were carried out at various temperatures ranging from 40–140 °C and with various frequencies ranging from 100 Hz–1 MHz along a- and c-directions by using the parallel plate capacitor method. Results indicate an increase of AC electrical parameters with the increase of temperature. The low εr values observed (around 4 at 40 °C) indicate that both LAA and LAO are promising low εr value dielectric materials. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Crystalline salts of amino acids have recently attracted considerable interest among researchers. L-arginine acetate (LAA) and Larginine oxalate (LAO) are two such materials. Several reports are available on them [1–8]. However, there is no report available, to the best knowledge of the authors, on the dielectric properties of these materials. LAA crystallizes in the monoclinic system with space group P21. The lattice parameters reported by Pal and Kar [4] are: a = 9.214(3)Å, b = 5.182 (2)Å, c = 13.222 (3) Å and β = 111.4 (1)°. LAA has a transmission range extending from 240 nm and could be used as an ultraviolet nonlinear optical (NLO) material. It is thermodynamically stable at least up to 200 °C. The measured density is 1.346 g/cc. LAO (α-form) crystallizes in the triclinic system with space group P1. The lattice parameters reported by Petrosyn et al. [7] are: a = 5.067 (1)Å, b = 9.767 (2)Å, c = 13.155 (3)Å, α = 111.11 (3)°, β = 92.81 (3)° and γ = 91.93 (3)°. Operation of electro-optic devices is based on the Pockel's effect, in which the change in the dielectric constant, Δεr, is a linear function of the applied field [9]. Permittivity characterization may yield some useful initial information. Microelectronics industry needs replacement of dielectric materials in multilevel interconnect structures with new low dielectric constant (εr) materials, as an interlayer dielectric (ILD) which surrounds and insulates interconnect wiring. Lowering the εr values of the ILD decreases the RC delay, lowers power consumption and reduces ‘cross-talk’ between nearby interconnects [10]. ⁎ Corresponding author. Tel.: +91 4652 261237. E-mail address: [email protected] (C.K. Mahadevan). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.04.047
Silica has εr ≈ 4.0, in part as a result of the Si–O bonds. Several innovative developments have been made for the development of new low-εr materials to replace silica. However, there is still a need for new low εr value dielectric materials. As the utility is in the electronic circuits with water proof condition, water soluble material in the single crystal form would be very much interesting. Recently, Goma et al. [11] have reported reduction in εr value in the case of potassium dihydrogen orthophosphate (KDP) added with 0.6 mol% urea. They observed at 40 °C, εr = 2.86 along a- and 3.17 along c-directions. This illustrates that urea doping to KDP reduces the εr value. In the present investigation, we have grown single crystals of LAA and LAO by the slow cooling method from the respective aqueous solutions and characterized the grown crystals by making dielectric measurements at various temperatures and with various frequencies. We report herein the results obtained. 2. Experimental Analytical reagent (AR) grade samples of L-arginine and oxalic acid along with double distilled water were used for the preparation of LAA and LAO. The salts were prepared by dissolving in water equimolar ratio of the respective acid and L-arginine and kept for the reaction to take place. The product was then purified by repeated crystallization until optically clear tiny crystals were obtained. Small (seed) crystals were grown from saturated aqueous solution by the free evaporation technique at constant temperature (30 °C). Good quality seed crystals were selected for the growth of large single crystals. Large size single crystals were grown by the slow cooling method using an optically heated constant temperature bath of
M. Meena, C.K. Mahadevan / Materials Letters 62 (2008) 3742–3744
3743
Mahadevan and his co-workers [11–13]. The observations were made while cooling the sample. Temperature was controlled to an accuracy of ±1 °C. Air capacitance (Cair) was also measured. Measurement along b-direction was not considered due to the small crystal thickness for both the crystals studied. Crystals with high transparency and surface defect-free (i.e. without any pit or crack or scratch on the surface, tested with a traveling microscope) were selected and used. The extended portions of the crystals were removed completely and the opposite faces were polished and coated with good quality graphite to obtain a good conductive surface layer. The dimensions of the crystals were measured using a traveling microscope (Least count = 0.001 cm). The dielectric constant of the crystal was calculated using the relation (as the crystal area was smaller than the plate area of the cell) [11] er ¼
Aair Acrys
Ccrys Cair 1 Acrys =Aair ; Cair
where Acrys is the area of the crystal touching the electrode and Aair is the area of the electrode. The AC conductivity (σac) was calculated using the relation [11] Fig. 1. Photographs of the grown crystals.
rac ¼ eo er xtand; control accuracy ± 0.01 °C set at 45 °C. A cooling rate of 0.5 °C per day was employed throughout the growth period (about 30 days). In both cases, the crystals grew along the c-direction. The growth rates were about 0.7 and 0.4 mm/day respectively for LAA and LAO crystals. The grown crystals were subjected to X-ray powder diffraction (XRD) measurements to confirm the material of the crystals grown. XRD data were collected from powdered samples using an automated X-ray powder diffractometer (PANalytical) with scintillation counter and monochromated CuKα (λ = 1.54056 Å) radiation. Analysis of the X-ray diffraction peaks was done by the available methods and lattice parameters were determined. The capacitance (Ccrys) and dielectric loss factor (tanδ) measurements were carried out to an accuracy of ±2% using an LCR meter (Agilant 4284A) with five different frequencies, viz. 100 Hz, 1 kHz, 10 kHz, 100 kHz and 1 MHz at various temperatures ranging from 40– 140 °C along a- and c-directions in a way similar to that followed by
Table 1 The εr, tanδ (×10− 2) and σac (×10− 8 mho/m) values at 40 °C Parameter
(i) For LAA (a) Along a-direction εr tanδ σac (b) Along c-direction εr tanδ σac (ii) For LAO (a) Along a-direction εr tanδ σac (b) Along c-direction εr tanδ σac
With a frequency of 100 Hz
1 kHz
10 kHz
100 kHz
1 MHz
4.036 3.4 0.076
3.831 2.9 0.609
3.669 0.98 1.99
3.577 0.79 15.7
3.417 0.43 81.9
4.281 4.1 0.097
4.072 3.1 0.704
3.903 1.0 2.27
3.807 0.83 17.6
3.503 0.50 97.5
3.942 3.9 0.085
3.901 3.7 0.796
3.861 3.3 7.11
3.831 3.1 67.0
3.721 2.8 582
4.276 4.6 0.108
4.127 4.4 0.998
4.072 4.2 9.46
3.957 4.0 87.1
3.903 3.8 823
Fig. 2. The dielectric constants for LAA.
3744
M. Meena, C.K. Mahadevan / Materials Letters 62 (2008) 3742–3744 along both a- and c-directions at all temperatures. This is a normal dielectric behaviour. This can be understood on the basis that the mechanism of polarization is similar to the conduction process. The electronic exchange of the number of ions in the crystal gives local displacement of electrons in the direction of the applied field, which in turn gives rise to polarization. The increase of conductivity with the increase in temperature observed for LAA and LAO in the present study is similar to that observed for some tartrate crystals [14]. Torres et al. [14] have explained the conduction mechanism in tartrate crystals by the rotation of the tartrate ions. When the temperature of the tartrate crystal is increased there is a possibility of weakening of the hydrogen bond system due to rotation of the tartrate ions. This results in an enhanced conduction in these materials. In the cases of LAA and LAO also, the conduction mechanism may be explained by the rotation of the acetate and oxalate ions as per the case. In the present study, it has been observed that the εr values (see Table 1) for LAA and LAO are significantly less (comparable to that of silica) for the pure material crystal itself. A suitable dopant added in a suitable concentration to LAA and LAO can be expected to reduce the εr value to a lower one as observed in the case of KDP single crystals added with urea. Thus, in effect, the present study indicates that LAA and LAO are not only potential NLO materials but also promising low εr value dielectric materials.
4. Conclusion LAA and LAO single crystals were grown by the slow cooling method from aqueous solutions and electrically characterized. The material of the grown crystals was confirmed. The present study indicates that the dielectric parameters, viz. εr, tanδ and σac increase with the increase in temperature. Also, it indicates that the εr and tanδ values decrease whereas the σac value increases with the increase in frequency along both a- and c-directions and at all temperatures. In addition, the results obtained in the present study indicate that LAA and LAO are not only potential NLO materials but also promising low εr value dielectric materials, expected to be useful in the microelectronics industry. Acknowledgement One of the authors (CKM) thanks the Defence Research and Development Organisation (DRDO), New Delhi for the grant of a Major Research Project. Fig. 3. The dielectric constants for LAO.
where εo is the permittivity of free space (8.85 × 10− 12 C2 N− 1 m− 2) and ω is the angular frequency. 3. Results and discussion The crystals grown in the present study (LAA to a size of 5 × 15 × 24 mm3 and LAO to a size of 4 × 6 × 17 mm3) are found to be stable, colourless and transparent. Fig. 1 shows their photographs. The XRD patterns (not shown here) obtained in the present study are essentially identical with the already published ones which confirm the materials of the grown crystals. The lattice parameters obtained [a = 9.174 (47)Å, b = 5.172 (14)Å, c = 13.478 (78)Å and β = 110.8 (2)° in the case of LAA; and a = 5.243 (2) Å, b = 9.892 (1) Å, c = 13.131 (2) Å, α = 111.1 (1)°, β = 92.8 (1)° and γ = 91.9 (1)° in the case of LAO] compare well with those obtained by the previous authors. The εr, tanδ and σac values obtained at 40 °C for both the crystals are given in Table 1. The values obtained at higher temperatures are not provided here to reduce the size of the table. However, as an illustration, the εr values obtained are shown in Figs. 2–3. In both cases, the εr, tanδ and σac values are found to increase with the increase in temperature along both a- and c-directions. The εr and tanδ values are found to decrease whereas the σac value is found to increase with the increase in frequency
References [1] Suresh CG, Vijayan M. Int J Pept Protein 1983;21:223. [2] Monaco SB, Davis LE, Velsko SP, Wang FT, Eimerl D, Zalkin A. J Cryst Growth 1987;85:252. [3] Chandra NR, Prabu MM, Venkatraman J, Suresh S, Vijayan M. Acta Crystallogr 1998;B54:257. [4] Pal T, Kar T. J Cryst Growth 2002;234:267. [5] Muralidharan R, Mohankumar R, Jayavel R, Ramasamy P. J Cryst Growth 2003;259:321. [6] Pal T, Kar T. Mater Chem Phys 2005;91:343. [7] Petrosyan AM, Sukiasyan RP, Karapetyan HA, Antipin MYu, Apreyan RA. J Cryst Growth 2005;275:e1927. [8] Selvaraju K, Valluvan R, Kirubavathi K, Kumararaman S. Mater Lett 2007;61:3041. [9] Boyd GT. J Opt Soc Am 1989;B6:685. [10] Hatton BD, Landskron K, Hunks WJ, Bennett MR, Shukaris D, Perovic DD, Ozin GA. Mater Today 2006;9(3):22. [11] Goma S, Padma CM, Mahadevan CK. Mater Lett 2006;60:3701. [12] Manonmani N, Mahadevan CK, Umayorubhagan V. Mater Manuf Process 2007;22:388. [13] Priya M, Mahadevan CK. Physica 2008;B403:67. [14] Torres ME, Peraza J, Yones AC, Lopez T, Stockel J, Marrero-Lopez D, Solans X, Bocanegra E, Silgo CG. J Phys Chem Solids 2002;63:695.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Growth and dielectric properties of L-arginine acetate and L-arginine oxalate single crystals M. Meena, C.K. Mahadevan ⁎ Physics Research Centre, S.T. Hindu College, Nagercoil — 629 002, Tamilnadu, India
A R T I C L E
I N F O
Article history: Received 22 February 2008 Accepted 10 April 2008 Available online 16 April 2008 Keywords: l-arginine acetate l-arginine oxalate Crystal growth Dielectric properties
A B S T R A C T Single crystals of L-arginine acetate (LAA) and L-arginine oxalate (LAO), potential nonlinear optical materials, have been grown from respective aqueous solutions by using the slow cooling method. X-ray diffraction measurements confirmed the material of the grown crystals. Dielectric measurements were carried out at various temperatures ranging from 40–140 °C and with various frequencies ranging from 100 Hz–1 MHz along a- and c-directions by using the parallel plate capacitor method. Results indicate an increase of AC electrical parameters with the increase of temperature. The low εr values observed (around 4 at 40 °C) indicate that both LAA and LAO are promising low εr value dielectric materials. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Crystalline salts of amino acids have recently attracted considerable interest among researchers. L-arginine acetate (LAA) and Larginine oxalate (LAO) are two such materials. Several reports are available on them [1–8]. However, there is no report available, to the best knowledge of the authors, on the dielectric properties of these materials. LAA crystallizes in the monoclinic system with space group P21. The lattice parameters reported by Pal and Kar [4] are: a = 9.214(3)Å, b = 5.182 (2)Å, c = 13.222 (3) Å and β = 111.4 (1)°. LAA has a transmission range extending from 240 nm and could be used as an ultraviolet nonlinear optical (NLO) material. It is thermodynamically stable at least up to 200 °C. The measured density is 1.346 g/cc. LAO (α-form) crystallizes in the triclinic system with space group P1. The lattice parameters reported by Petrosyn et al. [7] are: a = 5.067 (1)Å, b = 9.767 (2)Å, c = 13.155 (3)Å, α = 111.11 (3)°, β = 92.81 (3)° and γ = 91.93 (3)°. Operation of electro-optic devices is based on the Pockel's effect, in which the change in the dielectric constant, Δεr, is a linear function of the applied field [9]. Permittivity characterization may yield some useful initial information. Microelectronics industry needs replacement of dielectric materials in multilevel interconnect structures with new low dielectric constant (εr) materials, as an interlayer dielectric (ILD) which surrounds and insulates interconnect wiring. Lowering the εr values of the ILD decreases the RC delay, lowers power consumption and reduces ‘cross-talk’ between nearby interconnects [10]. ⁎ Corresponding author. Tel.: +91 4652 261237. E-mail address: [email protected] (C.K. Mahadevan). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.04.047
Silica has εr ≈ 4.0, in part as a result of the Si–O bonds. Several innovative developments have been made for the development of new low-εr materials to replace silica. However, there is still a need for new low εr value dielectric materials. As the utility is in the electronic circuits with water proof condition, water soluble material in the single crystal form would be very much interesting. Recently, Goma et al. [11] have reported reduction in εr value in the case of potassium dihydrogen orthophosphate (KDP) added with 0.6 mol% urea. They observed at 40 °C, εr = 2.86 along a- and 3.17 along c-directions. This illustrates that urea doping to KDP reduces the εr value. In the present investigation, we have grown single crystals of LAA and LAO by the slow cooling method from the respective aqueous solutions and characterized the grown crystals by making dielectric measurements at various temperatures and with various frequencies. We report herein the results obtained. 2. Experimental Analytical reagent (AR) grade samples of L-arginine and oxalic acid along with double distilled water were used for the preparation of LAA and LAO. The salts were prepared by dissolving in water equimolar ratio of the respective acid and L-arginine and kept for the reaction to take place. The product was then purified by repeated crystallization until optically clear tiny crystals were obtained. Small (seed) crystals were grown from saturated aqueous solution by the free evaporation technique at constant temperature (30 °C). Good quality seed crystals were selected for the growth of large single crystals. Large size single crystals were grown by the slow cooling method using an optically heated constant temperature bath of
M. Meena, C.K. Mahadevan / Materials Letters 62 (2008) 3742–3744
3743
Mahadevan and his co-workers [11–13]. The observations were made while cooling the sample. Temperature was controlled to an accuracy of ±1 °C. Air capacitance (Cair) was also measured. Measurement along b-direction was not considered due to the small crystal thickness for both the crystals studied. Crystals with high transparency and surface defect-free (i.e. without any pit or crack or scratch on the surface, tested with a traveling microscope) were selected and used. The extended portions of the crystals were removed completely and the opposite faces were polished and coated with good quality graphite to obtain a good conductive surface layer. The dimensions of the crystals were measured using a traveling microscope (Least count = 0.001 cm). The dielectric constant of the crystal was calculated using the relation (as the crystal area was smaller than the plate area of the cell) [11] er ¼
Aair Acrys
Ccrys Cair 1 Acrys =Aair ; Cair
where Acrys is the area of the crystal touching the electrode and Aair is the area of the electrode. The AC conductivity (σac) was calculated using the relation [11] Fig. 1. Photographs of the grown crystals.
rac ¼ eo er xtand; control accuracy ± 0.01 °C set at 45 °C. A cooling rate of 0.5 °C per day was employed throughout the growth period (about 30 days). In both cases, the crystals grew along the c-direction. The growth rates were about 0.7 and 0.4 mm/day respectively for LAA and LAO crystals. The grown crystals were subjected to X-ray powder diffraction (XRD) measurements to confirm the material of the crystals grown. XRD data were collected from powdered samples using an automated X-ray powder diffractometer (PANalytical) with scintillation counter and monochromated CuKα (λ = 1.54056 Å) radiation. Analysis of the X-ray diffraction peaks was done by the available methods and lattice parameters were determined. The capacitance (Ccrys) and dielectric loss factor (tanδ) measurements were carried out to an accuracy of ±2% using an LCR meter (Agilant 4284A) with five different frequencies, viz. 100 Hz, 1 kHz, 10 kHz, 100 kHz and 1 MHz at various temperatures ranging from 40– 140 °C along a- and c-directions in a way similar to that followed by
Table 1 The εr, tanδ (×10− 2) and σac (×10− 8 mho/m) values at 40 °C Parameter
(i) For LAA (a) Along a-direction εr tanδ σac (b) Along c-direction εr tanδ σac (ii) For LAO (a) Along a-direction εr tanδ σac (b) Along c-direction εr tanδ σac
With a frequency of 100 Hz
1 kHz
10 kHz
100 kHz
1 MHz
4.036 3.4 0.076
3.831 2.9 0.609
3.669 0.98 1.99
3.577 0.79 15.7
3.417 0.43 81.9
4.281 4.1 0.097
4.072 3.1 0.704
3.903 1.0 2.27
3.807 0.83 17.6
3.503 0.50 97.5
3.942 3.9 0.085
3.901 3.7 0.796
3.861 3.3 7.11
3.831 3.1 67.0
3.721 2.8 582
4.276 4.6 0.108
4.127 4.4 0.998
4.072 4.2 9.46
3.957 4.0 87.1
3.903 3.8 823
Fig. 2. The dielectric constants for LAA.
3744
M. Meena, C.K. Mahadevan / Materials Letters 62 (2008) 3742–3744 along both a- and c-directions at all temperatures. This is a normal dielectric behaviour. This can be understood on the basis that the mechanism of polarization is similar to the conduction process. The electronic exchange of the number of ions in the crystal gives local displacement of electrons in the direction of the applied field, which in turn gives rise to polarization. The increase of conductivity with the increase in temperature observed for LAA and LAO in the present study is similar to that observed for some tartrate crystals [14]. Torres et al. [14] have explained the conduction mechanism in tartrate crystals by the rotation of the tartrate ions. When the temperature of the tartrate crystal is increased there is a possibility of weakening of the hydrogen bond system due to rotation of the tartrate ions. This results in an enhanced conduction in these materials. In the cases of LAA and LAO also, the conduction mechanism may be explained by the rotation of the acetate and oxalate ions as per the case. In the present study, it has been observed that the εr values (see Table 1) for LAA and LAO are significantly less (comparable to that of silica) for the pure material crystal itself. A suitable dopant added in a suitable concentration to LAA and LAO can be expected to reduce the εr value to a lower one as observed in the case of KDP single crystals added with urea. Thus, in effect, the present study indicates that LAA and LAO are not only potential NLO materials but also promising low εr value dielectric materials.
4. Conclusion LAA and LAO single crystals were grown by the slow cooling method from aqueous solutions and electrically characterized. The material of the grown crystals was confirmed. The present study indicates that the dielectric parameters, viz. εr, tanδ and σac increase with the increase in temperature. Also, it indicates that the εr and tanδ values decrease whereas the σac value increases with the increase in frequency along both a- and c-directions and at all temperatures. In addition, the results obtained in the present study indicate that LAA and LAO are not only potential NLO materials but also promising low εr value dielectric materials, expected to be useful in the microelectronics industry. Acknowledgement One of the authors (CKM) thanks the Defence Research and Development Organisation (DRDO), New Delhi for the grant of a Major Research Project. Fig. 3. The dielectric constants for LAO.
where εo is the permittivity of free space (8.85 × 10− 12 C2 N− 1 m− 2) and ω is the angular frequency. 3. Results and discussion The crystals grown in the present study (LAA to a size of 5 × 15 × 24 mm3 and LAO to a size of 4 × 6 × 17 mm3) are found to be stable, colourless and transparent. Fig. 1 shows their photographs. The XRD patterns (not shown here) obtained in the present study are essentially identical with the already published ones which confirm the materials of the grown crystals. The lattice parameters obtained [a = 9.174 (47)Å, b = 5.172 (14)Å, c = 13.478 (78)Å and β = 110.8 (2)° in the case of LAA; and a = 5.243 (2) Å, b = 9.892 (1) Å, c = 13.131 (2) Å, α = 111.1 (1)°, β = 92.8 (1)° and γ = 91.9 (1)° in the case of LAO] compare well with those obtained by the previous authors. The εr, tanδ and σac values obtained at 40 °C for both the crystals are given in Table 1. The values obtained at higher temperatures are not provided here to reduce the size of the table. However, as an illustration, the εr values obtained are shown in Figs. 2–3. In both cases, the εr, tanδ and σac values are found to increase with the increase in temperature along both a- and c-directions. The εr and tanδ values are found to decrease whereas the σac value is found to increase with the increase in frequency
References [1] Suresh CG, Vijayan M. Int J Pept Protein 1983;21:223. [2] Monaco SB, Davis LE, Velsko SP, Wang FT, Eimerl D, Zalkin A. J Cryst Growth 1987;85:252. [3] Chandra NR, Prabu MM, Venkatraman J, Suresh S, Vijayan M. Acta Crystallogr 1998;B54:257. [4] Pal T, Kar T. J Cryst Growth 2002;234:267. [5] Muralidharan R, Mohankumar R, Jayavel R, Ramasamy P. J Cryst Growth 2003;259:321. [6] Pal T, Kar T. Mater Chem Phys 2005;91:343. [7] Petrosyan AM, Sukiasyan RP, Karapetyan HA, Antipin MYu, Apreyan RA. J Cryst Growth 2005;275:e1927. [8] Selvaraju K, Valluvan R, Kirubavathi K, Kumararaman S. Mater Lett 2007;61:3041. [9] Boyd GT. J Opt Soc Am 1989;B6:685. [10] Hatton BD, Landskron K, Hunks WJ, Bennett MR, Shukaris D, Perovic DD, Ozin GA. Mater Today 2006;9(3):22. [11] Goma S, Padma CM, Mahadevan CK. Mater Lett 2006;60:3701. [12] Manonmani N, Mahadevan CK, Umayorubhagan V. Mater Manuf Process 2007;22:388. [13] Priya M, Mahadevan CK. Physica 2008;B403:67. [14] Torres ME, Peraza J, Yones AC, Lopez T, Stockel J, Marrero-Lopez D, Solans X, Bocanegra E, Silgo CG. J Phys Chem Solids 2002;63:695.