spie proceedings [spie optics & photonics 2005 - san diego, ca (sunday 31 july 2005)]...

Investigation on the Growth Kinetics of KDP: LAP and TGS: LAPSingle Crystals

A. K. Batra, J. Stephens, K. Bhat, M. D. Aggarwal, Burl H. Peterson,Michael Curley and R. B. Lal*

Department of PhysicsP0 Box 1268, Alabama A&M University, Normal, AL 35762 (USA)

ABSTRACT

Potassium dihydrogen phosphate KDP; (KH2PO4)) and triglycine sulfate TGS; (CH2NH2COOH.H2S04), areextensively studied ferroelectric materials, and find wide applications in electrooptic and infrared detecting devicesrespectively. L-arginine phosphate monohydrate (C6H14N402H3P04.H20), abbreviated as LAP, is a highlytransparent monoclinic crystal with attractive properties for efficient frequency conversion of infrared lasers. Effectsof doping KDP and TGS crystals with LAP are investigated. It was found in both cases that LAP affects the growthmorphology and other properties. The properties of resulting crystals in terms of growth morphology, optical andmechanical properties are presented and discussed.

Key words: KDP, LAP, TGS, NLO crystals, Solution crystal growth

1. INTRODUCTION

Potassium dihydrogen phosphate KDP; (KH2PO4) and it derivatives are used in various optical devices[1-2]. KDP crystals are widely used as the second, third and fourth harmonic generators for Nd:YAG lasers.Srinivasan et al., studied the effects of KDP on ADP crystals by growing mixed crystals of KDP:ADP [3]. Ravi etal., investigated the growth of sulfate mixed L-arginine phosphate and ADP/KDP mixed crystals. It was reportedthat partial substitutions of sulfate in LAP improves the growth rate, and mixed crystals are more easily cleavable[4]. Arunmozhi et a!., have reported the effect of antiferroelectric ADP doping on ferroelectric TGS crystals [5].They found that the morphology of the mixed crystals is similar to triglycine sulfate: phosphate (TGS:TGP) crystalsand significant amount of phosphate is incorporated into the lattice. No change in the nature of ferroelectric phasetransition in these mixed crystals was observed. TGS crystals among other available materials [6-8] havetechnological importance in infrared detection, thermal imaging and other infrared sensing applications, because oftheir high pyroelectric coefficient and relatively low dielectric constants at room temperature. Pyroelectric sensorsbased on TGS are uniformly sensitive to radiations in wavelength range from ultra-violet to far infrared, and do notrequire cooling for operation, as compared to quantum detectors, where low temperature cooling is required. Thecrystal structure of TGS is monoclinic below the Curie temperature (Ta'— 49°C). The crystal elements perpendicularto [010] crystallographic direction (which is also a cleavage plane) are used for detector fabrication. Many effortshave been made in the past to understand the growth mechanism and improve its pyroelectric, mechanical, opticaland ferroelectric properties and to prevent depolarization due to thermal, electrical or mechanical means [6-27].Efforts are mainly focused towards understanding the growth mechanism, growth rate and modifying the desiredpyroelectric properties by doping TGS crystals with inorganic and organic dopants. There are some disadvantages inpure TGS crystals, namely its tendency to depolarize, low temperature range of operation and thermal hysteresis ofvariables defining the pyroelectric figures-of-merit [7]. To avoid these disadvantages, TGS crystals doped with

* Present Address: NASA Administrators Fellow, Exploration Science and Technology Division, XD4O, NASA -Marshall Space Flight Center, Alabama 35812, U.S.A.

Operational Characteristics and Crystal Growth of Nonlinear Optical Materials II, edited by Ravindra B. Lal,Donald O. Frazier, Proc. of SPIE Vol. 5912, 591206, (2005) · 0277-786X/05/$15 · doi: 10.1117/12.611418

Proc. of SPIE Vol. 5912 591206-1

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amino acids, including L-alanine [26] and other dipolar organic dopants, such as urea and nitro-anilines have beenaffective in reducing depolarization, and in increasing the pyroelectric figures-of-merit. Other approaches havebeen to grow mixed crystals of triglycine sulfate: phosphate (TGS:TGP) to increase its pyroelectric performance[28-29]. However, TGS crystals doped with L-alanine are found to be the best in checking the depolarization [27].They become fragile, and break when samples are prepared in the form of extremely thin elements for use ininfrared devices.

In light of research work being done on KDP and TGS crystals, to improve their growth and othercharacteristics, it was thought interesting and worthwhile to investigate the effects of LAP (which is an amino-acidlike glycine) on growth, morphology, and optical properties of TGS crystals. In case of TGS crystals, we believethat L-arginine may act as a dopant, similar to L-alanine, to check the tendency to depole, while the phosphatecomponent may improve its pyroelectric performance as it has been found in mixed triglycine sulfate: phosphate(TGS:TGP) crystals [28-29]. Effects of LAP on KDP crystals are studied for academic interests. Beforeinvestigating the above-cited parameters, one has to study growth kinetics. In this paper, we report the results ofinvestigation of the effects of L-arginine phosphate on growth of KDP and TGS crystals [(TGS):(LAP)1 and(KDP):(LAP)1 with various values ofx (wt%)] along with their optical and mechanical properties.

2. EXPERIMENTAL, RESULTS AND DISCUSSION

2. 1 Preparation and Characterization of Crystals

Crystal growth: The crystals were grown by isothermal evaporation technique at room temperature. Themorphology and quality of the crystals were visually inspected.

Infrared spectra: The JR spectra of the crystals were taken by a Bomem 320 FT-JR at room temperature.The samples for FTIR were prepared by grounding them into a fine powder and then taking the reflectancespectra. The infrared spectra were taken from 500 to 4000 crri1 (wave-number).

Visible spectra: The visible spectra of all the polished crystals were taken by using Perkins Elmerspectrophotometer.

S.H.G measurements were performed by usual method. The details are given elsewhere [29a].

Micro-hardness measurements were made at room temperature using Leitz Wetzler tester with Vickers'spyramidal diamond indentor with a force of fifty grams for a length of 30 seconds.The Vicker's hardness (Hr) was estimated from the relationship:

H= 1.8544/Pd2,

where load (P) is in kilograms and the diagonal length of indentation (d) is measured in micrometers. 1.8544is a constant of geometric factor for diagonal pyramid. At least 5-10 indentations were made and mean arithmeticvalues ofthe measured two diagonals (d) were used for the calculations ofthe hardness

3. RESULTS AND DISCUSSION

The photographs of KDP:LAP and TGS:LAP crystals along with comments are given in Table 1 and Table2 respectively. One can infer that there is a change in crystal morphology on doping with L-arginine phosphate. Thechange in the morphology is significant in KDP and TGS crystals grown with 30 wt% and 20% LAP in the solutionrespectively [Tables 1—2]. With 30 wt% of LAP in the KDP solution, needle shaped crystals joined together at thenucleation site were produced. In the case of TGS crystals grown with 20 wt. % of L-arginine phosphate in thesolution, growth along [001] crystallographic direction is greatly reduced. Thus, crystals become plate-like as shownin Table 2. With higher concentration of dopant in TGS solution, the crystals became flake-like (not shown). Thenumbers of faces are also reduced.



It is known for a long time that impurities affect the growth and morphology of crystals [30] especially ifthey are grown from solution. Several review articles have been written in the recent past on this area [3 1 -33]. Aparticular impurity may act differently on different crystallographic directions in changing the physical and chemicalproperties. Certain impurities (dopants) are useful in changing the properties of crystals while others may not. Someimpurities, which act like a poison, can completely stop the growth in a particular direction. Some dopants may gointo the crystal lattice interstitially or replace the host lattice while other may not go into the lattice but alters thegrowth or habit of crystals. Various theories and models have been proposed in the past to explain the phenomenon[31-34]. These effects can be explained on the basis of kinetic or surface energy theories. However, combinedfactors can not be ruled out such as: solubility of host and the impurity phase; character of the mother phase;interaction between the host and the impurity molecules; relative size of impurity and host ions; the similarity in thecrystallographic structure of the two phases; relative size of the impurity and the host ions; and other crystallizationconditions such as pH of the solution. In our study of 7OKDP:3OLAP, crystal growth of 'crystal bunch' is fasteralong [00 1] direction (assumed that is why needle shaped crystals are formed ), may be due to a decrease in thesurface free energy. In the case of 7OTGS:30 LAP, growth along [001] crystallographic direction is decreased; itmay be due to kinetic effect involving a decrease in the value of the kinetic coefficient for the motion of the steps,as explained in adsorption model [34].

Effects of pH on the growth of doped crystals are also investigated. It was found that in the case ofKDP:LAP crystals, the 'visual optical quality' was improved at certain pH of the solution. The pH was changed byadding phosphoric acid, thereby increasing the phosphate ions , which may diffuse slowly, thus producing crystalsof good 'visual optical quality' . The change in optical quality was not found in the growth of TGS crystals. It maybe possible that phosphate ions of LAP may replace some of the sulfate ions as seen in (TGSTGP1) crystals [28-29].

The UV-VIS spectra is important crystals, as compare with pure TGS crystals in UV-Vis range. Thechange in transmittance was observed in 1OKDP:9OLAP crystals over pure KDP crystals. The calculated band edgeofvarious crystals is tabulated in table 3.

FT1R spectroscopy is a powerful tool in fingerprinting various molecules and type of internal molecularvibrations. The spectra for TGS, LAP and 95TG5:5LAP crystals are shown in Fig. I (a) to Fig 1(c). For brevity thefrequency assignments to various observed bands are also tabulated in Table 4 and are self-explanatory illustratingvarious bands. Our objective is to find out whether P043 or/and HPO42 (L-arginine components) have entered theTGS lattice. The assignments in spectra of Fig. 1 (c) show the presence of phosphate group band between 1050-1 100 cm1 36]. Furthermore, it is known that in P-OH stretching is observed at 950 and 1032 cm-l [36]. Tn our casewe observed at 976 cm' . However, further studies in terms of growth of larger TGS:LAP crystals by solutiontemperature lowering method should be conducted to come to conclusive results. Such experiments are planned.

In second harmonic generation studies (SHG), it was observed that scattered light from the sample, 95KDP:SLAP, when illuminated with infrared radiation of 1 .064-micron wavelength has a peak wavelength of 532.5 1 1,which is second harmonic of the input infrared radiation. Furthermore, it was also found that dependence of outputpower to input power is nonlinear, and the output power is proportional to square power of the input. The slopeinput power to output power was 1 .967 on a log scale (Fig. 2). This is additional evidence that the scattered light is asecond harmonic of the JR input. Further work is needed in this direction for comparison with well known KDP orLAP crystals.

The mechanical properties are impornant factors. T11e micro-hardness of TGS:LAP crystals is tabulated inTable 5 It decreased with increase of LAP concentration in the solution.



4. CONCLUSION

The preliminary results of our investigation are summarized below:

1 . The crystals of triglycine sulfate and potassium dihydrogen phosphate doped with various concentrations ofL-arginine phosphate were grown by isothermal slow evaporation method. The doping with LAP affectsthe morphology ofboth the crystals.

2. With more than 30 wt% of LAP in the solution, grown crystals of KDP were needle-like joined together atthe nucleation site. With more than 20 wt% of LAP in the TGS solution, growth along c-direction isrestricted and pentagon-shaped crystals were formed.

3. The band edge of doped TGS crystals did not change, while in the case of doped KDP crystals, a changewas observed.

4. A second harmonic generation peak at a wavelength 532.5 1 1 nm was observed when the samples of95KDP: 5LAP were illuminated with IR radiation of 1.064-micron wavelength.

5. The mechanical properties, such as Vickers' hardness decreased on doping.

6. Larger crystals of TGS:LAP should be grown using the temperature solution lowering technique. Theproperties of crystals with optimum concentration (which produces good quality crystals) of LAP in thesolution should be investigated, in order to assess their merits, for use in infrared detecting devices.

ACKNOWLEDGEMENTS

Special thanks to Dr. S. Sarkisov for allowing us to use his facilities for optical characterization ofsamples and for suggestions. One of us (RBL) appreciates the support of the NASA AdministratorFellowship, administered by the United Negro Fund Special Programs Corporation.



REFERENCES

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[2] L. N. Rashkovich, KDP Family ofSingle Crystals', Adam Hilger, NY(1991).[3] K. Srinivasan, P. Ramasamy, A. Cantono, G. Boclli, Mat. Sci. and Eng., 852 (1998) 129.[4] G. Ravi, K. Srinivasan, S. Anbukumar, R. Ramasamy, J. Cryst. Growth 137 (1994) 589.[5] G. Arunmozhi, S. Lanceros, S. Lanceros-Mendez, E. de. Matos Gomes, Mat. Lett., 54 (2002) 329.[6] R. B. La!, A. K. Batra, Ferroe!ectrics 142 (1993) 51.[7] S. B. Lang and D. K. Das-Gupta, Ferroelectric. Rev., 2(3-4) (2000) 217.[8] H. V. Alexandru, C. Berbecaru, F. Stanculescu, L. Pintile, I. Matei, M. Lisca, Sensors and Actuators A 1 13

(2004) 387.[9] C. Berbecaru, H. V. A!exandru, L. Pintile,, A. Dutu, B. Logofatu, R. C. Radulescu, Mat. Sci. & Engn. B.

xxx (2005) XX ( in press).[10]. J.-M. Chang, A. K. Batra, and R. B. La!, Crys. Grow. and Des., 7 (2002) 431.[1 1]. R. W. Whatmore, Rep. Prog. Phys., 49 (1986) 1335.[12] M. Banan, R. B. La!, A. K. Batra, J. Mat. Sci. 27 (1992) 2291.[13] Jiann-Min.Chang,A. K. Batra, R. B. La!, J. Cryst. Growth 158 (1996) 284.[14] X. Sun, M. Wang, Q. W. Pan, W. Shi, C. S. Fang, Cryst. Res. Technol. 34(1O)(1999) 1251.[15] K. Meera, R. Muralidaran, A. K. Tripathi, R. Dhanasekaran, P. Ramasamy, J. Cryst. Growth

260 (2004) 414.[16] K. Meera, S. Aravazhi, P. S. Raghavan, P. J. Ramasamy, J. Cryst. Growth 221 (2000) 220.[17] S. Ka!ainathan, M. Beatrice Margaret, T. Irusan, Crystal Engn., 5 (2002) 71.[18] K. Meera, R. Muralidaran, A. K. Tripathi, P. Ramasamy, J. Cryst. Growth 263 (2004) 524.[19] S. Aravazhi, R. Jayave!, C. Subramanium, Mat. Res. Bull., 32(1 1) (1997) 1 503.[20] R. Mohan kumar, R. Muralidaran, D. R. Babu, K. V. Rajendra, Jayavel, R, P. Ramasamy,

J. Cryst. Growth 229 (2001) 568.[21] S. Aravazhi, R. Jayavel, C. Subramanium, Mol. Chem. Phys. 50 (1997) 57.[22] K. Meera, R. Muralidaran, P. Santhanaraghavan, R. Gopa!akrishanan, P. Ramasamy, J. Cryst. Growth. 226

(2001) 303.[23] K. Meera, R. Muralidaran, P. Santhanaraghavan, R. Gopalakrishanan, P. Ramasamy, J. Cryst. Growth 260

(2000) 220.[24] K. Meera, R. Muralidaran, P. Santhanaraghavan, R. Gopa!akrishanan, P. Ramasarny, J. Cryst. Growth 263

(2004) 524.[25] 5. Ramos, J. D. Cerro, J. M. Martin, B. Brezina, M. Havrankova, Ferroe!ctrics 157 (1994) 293.[26] Jiann-Min.Chang, A. K. Batra, R. B. La!, Cryst. Growth. & Design 5(2) (2002) 431.[27] K. L. Bye, P. W. Whipps, E. T. Keve, Ferroelectrics 4 (1972) 253.[28] Aparna Saxena, Vinay Gupta, K. Sreenivas, J. Crys. Growth 263 (2002) 192.[29] C. S. Fang, Y. Xi, A. S. Bha!la, L. E. Cross, Ferroelectrics 2639 2004) 9.[29a] A. K. Batra, Tesfaye Gebre, K. Bhat, M. D. Aggarwal, B. Peterson, S. Sarkisov, R. B. La!, Proc. SPIE, Vol.

5212, (2003) 57.[30] F. J. Jong, S. J. Jancic (Eds), Industrial Crystallization, vol. 78, North-Holand, Amsterdam,[3 1] E. Kirkova, B. Djarova, B. Djaova, B. Donkova, Prog. Cryst. Growth Charact., 32 (1996) 117.[32] K. Sangwa!, J. Cryst. Growth 203 (1999) 197.[33] K. Sangwa!, Prog. Cryst. Growth. Charact. 32 (1996) 3.[33] V. A. Kuznetsov, T. M. Okhrimenko, M. Rak, J. Cryst. Growth 193 (1998) 164.[34] Se!emanni, Kama!a Bhat, Ashok K. Batra, Mohan D. Aggarwa!, Ravindra B. La! Mat. Lett. 58 (2004) 991.[35] A. Abu El-Fad!, J. Phys. Chem. So!., 60 (1999) 1881.[[36] A. S. Haja Hameed, G. Ravi, MD. M. Hossian, P. Ramasamy, J. Cryst. Growth 204 (1999).



Table 1 Habits of TGS:LAP Crystals

TGS:LAP

Crystal(Sample Name)

Comments Morphology

100% TGS(TGS)

Large rectangularshape crystal

95% TGS: 5% LAP Large pentagon(95TGS5LAP) shape crystal

90% TGS:10%LAP

(9OTGS 1 OLAP

Large pentagonshape crystal

85%TGS: 15%LAP

(85TGS 1 SLAPNot Available Not Available

80% TGS: 20%LAP

(8OTGS2OLAP

Large flatpentagon shape

crystal



100%KDP(KDP)

Table 2 Habits of KDP:LAP crystals

Rectangular shapewith pyramid

structures at eachend

KDP:LAP

Crystal(Sample_Name)

Comments Morphology

Large and long99% KDP: I % LAP

(99KDP1LAP)

rectangular shapewith pyramid

structures at eachend

Large rectangular95% KDP: 5% LAP shape with pyramid(95KDP5LAP) structures at each

end

Large rectangular93% KDP: 7% LAP shape with pyramid

(93KDP7LAP) structures at eachend

Large rectangular90% KDP: 10% LAP shape with pyramid

(9OKDP1OLAP) structures at eachend

70% KDP:

(7OKDP3OLAP)30% LAP Needle shaped

crystals



Table 3 Band edge of pure and doped crystals

Material Band Edge /

TGS 4.9eV/253nm

KDP 4.4eV/282nm

LAP 3.4eV/365nm

90% TGS 10% LAP 4.9 eV /253 nm

80%TGS 20% LAP 4.8 eV/259nm

93% KDP 7%LAP 3.7 eV / 336 nm

90% KDP 10% LAP 4.4 eV / 282 nm



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Table 5 Vicker's hardness of doped crystals

Sample Name Vicker'sHardness(kg/mm2)

Test Face

LAP240 (001)

TGS210.8 (001)

95TGS5LAP133 (001)

9OTGS1OLAP136

(001)

85TGS15LAP61.6 (001)

8OTGS2OLAP67.6 (001)

Proc. of SPIE Vol. 5912 591206-10


102

100

98

969)

94

92

90

88

86

100

95

90

C 856)

80

75E

70

H 65

60

55

TGS Pure

8)

E

100

95

90

85

80

3000 2500 2000 1500

W avenum ber in cm1

Fig. 1 (a). FTIR spectrum of TGS crystal

2000 1500

Wavenumber in cm1

Fig. 1 (b). FTIR spectrum of LAP crystal

Wavenumberin cm

Fig. 1(c). FTIR spectrum of TGS: LAP crystal

Proc. of SPIE Vol. 5912 591206-11


1.0-

5LAPKDP xtal final figure0.8

horizontal polarization06 1064nm ,-U

UV filter (1)• 'U• 0.4 slope 1.967

xtal structure 001

I ::xtal polarization unk:wn

o -0.2

080'8 019

•

1'O l'i 1'2 1'3 1'4 1'5 16

Log (power input [mW})

Fig. 2. Output power versus the power of pumping IR radiationin the crystal of 95KD5LAP in log-log scale.

Proc. of SPIE Vol. 5912 591206-12


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