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CHAPTER 6

COMPARATIVE STUDIES ON CONVENTIONAL AND

SANKARANARAYANAN-RAMASAMY (SR) METHODS

GROWN POTASSIUM SODIUM TARTRATE

TETRAHYDRATE SINGLE CRYSTALS

6.1 INTRODUCTION

In recent years, owing to a number of practical applications in the

field of micro-electronics and optoelectronics, a great deal of interest has been

shown to study the properties of various materials (Arora et al 2004, Kamba

et al 1995 and Shiozaki et al 1998). Semi-organic crystals which have the

combined properties of both inorganic and organic crystals like wide

transparency range and nonlinear coefficients which make them suitable for

device fabrication (Meng Fanqing et al 1996). Rochelle salt is optically active

(Beevers and Hughes 1941), strongly piezoelectric because tartaric acid is a

chiral molecule exhibiting a non-centrosymmetrical structure can be easily

obtained when tartaric acid reacts with some bases (Fitzgerald and Casabella

1973).

The Rochelle salt is of particular interest as it exhibits a

ferroelectric phase between 255 and 297 K, where the structure is monoclinic

with a space group of P21, above the temperature of 297 K the compound is

paraelectric and exhibits orthorhombic phase in space group P21212 (Myerson

et al 1996). Investigation on dielectric properties of Rochelle salt show

anomalies at low temperature. The tartrate molecules lie in three planes,

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bonded to sodium and potassium atoms directly through a medium of water

molecules (Gallagher et al 2003). Earlier reports infer that Rochelle salt (RS)

has two sublattices, in high temperature neither of the sublattices is polarised

hence the crystal is not ferroelectric (Bleay et al 1978 and Ubbelohde and

Woodward 1946). Crystals of different orientations with different

morphology are grown by conventional solution growth technique but from

application point of view, specific orientation with good quality is needed.

Crystallization from solution is an important process and the

driving force for crystallization is the degree of supersaturation, which has

been commonly expressed as the difference in concentration between the

supersaturated and saturated solutions (Brice 1986). A novel unidirectional

growth method of Sankaranarayanan-Ramasamy (SR) (Sankaranarayanan

2005) has been introduced for the growth of unidirectional single crystals

from solution. This technique has been already applied to grow some organic

(Benzophenone) and inorganic (KDP) crystals (Sankaranarayanan and

Ramasamy 2005a). SR method grown crystals are shown to be better than the

conventional solution grown crystals. Hence unidirectional growth method of

Sankaranarayanan-Ramasamy (SR) from solution is employed to grow

potassium sodium tartrate tetrahydrate (PST) bulk single crystals.

6.2 EXPERIMENTAL PROCEDURE

6.2.1 Solubility and Growth of Potassium Sodium Tartrate

Tetrahydrate

Commercially available potassium sodium tartrate tetrahydrate salt

was used for growth. The solubility of PST was estimated using water as a

solvent at different temperatures (25-45C) in a constant temperature bath

attached with a cryostat, with an accuracy of ± 0.01C and the plot is shown

in Figure 6.1. It is inferred that the compound exhibits good solubility and has

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positive solubility temperature gradient. Figure 6.2 shows the molecular

structure of PST.

Figure 6.1 Solubility diagram of potassium sodium tartrate tetrahydrate

The schematic diagram of SR method which is employed for the

growth of potassium sodium tartrate tetrahydrate single crystal is shown in

Figure 6.3. From the solubility data PST single crystal was grown by slow

cooling solution growth technique using the recrystallized salt of PST. The

seed crystal was grown by conventional slow evaporation solution growth

method and (100) plane of the seed crystal was selected for unidirectional

crystal growth. The SR growth ampoule was rinsed with acetone and kept in a

hot oven. A PST seed crystal with (100) orientation was mounted at the

bottom of the growth ampoule. The charge material was dissolved in the

water solvent and the solution was stirred with the help of magnetic stirrer to

get the homogeneous mixture.

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The saturated solution was filtered using Whatman filter paper and

filled into the growth ampoule. The growth ampoule was sealed with

polyethylene sheet to control the evaporation of the solvent. The SR growth

ampoule with solution was housed in a constant temperature bath at 35C for

slow cooling. In this technique, a constant temperature bath attached with a

cryostat was used to cool the solution in the range of 0.5C in two days. Good

transparent single crystals of PST were harvested from the mother solution.

The grown unidirectional crystal, cut and polished wafer and cylindrical

morphology crystal are shown in Figure 6.4 (a, b and c).

The shape of the crystal depends on the shape of the growth

ampoule used. In the slow evaporation solution growth technique (SEST)

crystal grown from the solution is mainly due to materials available to grow,

whereas in the unidirectional SR method the seed is fixed in a preferred

orientation in the glass ampoule and the specific orientation of the seed is in

contact with its mother solution and the temperature is optimized. Due to

gravity induced concentration gradient the saturated solution which is in

contact with the seed initiates its growth. Figure 6.5 (a and b) shows the

conventional solution grown PST crystal and morphology. Under suitable

saturation and temperature further growth of crystal can be seen by attracting

more amounts of growth units towards the seed crystal.

Figure 6.2 Molecular structure of potassium sodium tartrate

tetrahydrate

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Figure 6.3 Schematic of experimental setup of Sankaranarayanan-

Ramasamy (SR) method

Figure 6.4 (a) SR method grown PST crystal (b) Cut and polished SR

method grown PST crystal (c) Cylindrical shape of grown

PST crystal

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Figure 6.5 (a) Conventional solution method grown single crystal of

PST (b) Morphology of PST crystal

6.3 CHARACTERIZATION

The grown single crystal of PST was subjected to single crystal

X-ray diffraction as well as powder X-ray diffraction analyses. From the

X-ray diffraction studies, it is confirmed that the grown crystal belongs to the

orthorhombic crystal system. The structural perfection of the grown crystals

was analyzed from the diffraction curve (DC) using High Resolution X-ray

diffraction (HRXRD). Vibrational assignments of the functional groups were

obtained from FT-IR/Raman spectra. The UV-Visible spectral studies were

carried out to analyze the optical properties of the grown crystal. The

mechanical behavior of the crystal was studied on (100) plane using Vickers

microhardness tester. Dielectric studies reveal the dielectric behavior at room

temperature by varying the frequencies from 100 Hz-5 MHz. Laser damage

threshold studies were carried out for the grown single crystals.

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6.4 RESULTS AND DISCUSSION

6.4.1 Structural Analysis

(i) Single crystal XRD

The single crystal XRD data of the grown PST crystals were

obtained and the lattice parameters are a = 11.884(2) Å, b = 14.256(4) Å,

c = 6.228(1) Å, and V = 1055.1 (4) Å3 which are in good agreement with the

literature (Beevers and Hughes 1941 and Görbitz and Sagstuen 2008). The

values are tabulated and compared with literature in Table 6.1.

Table 6.1 Lattice parameters of potassium sodium tartrate tetrahydrate

Lattice constant Present value

(Beevers and Hughes 1941)

(Görbitz and Sagstuen 2008)

a (Å) 11.884 (2) 11.93 11.878

b (Å) 14.256 (4) 14.30 14.246

c (Å) 6.228 (1) 6.17 6.218

(ii) Molecular structure

Beevers and Hughes (1941), Görbitz and Sagstuen (2008) have

reported the crystal packing arrangement of PST in the P21212 structure. The

PST is represented by alternating layers of cations and anions, including water

of crystallization. The cation layers consist of sodium ions, occupying general

positions and potassium ions, occupying two pairs of special positions. The

sodium ions are surrounded by two carboxyl oxygen, a hydroxyl group and

three water molecules. The K1 atoms (0, 0) are surrounded by two carboxyl

oxygens and two water molecules. The other potassium ions, K2 (0,½), are

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surrounded by two carboxyl oxygens, two hydroxyl groups and four water

molecules.

The tartrate ions are kinked chains of carbon atoms lying in two

mutually perpendicular planes. The whole structure has infinite helical chains

of O-H.…O hydrogen bonds between the molecules of water of

crystallization and the oxygen atoms of the anions. The unit cell of the crystal

contains four molecules of KNaC4H4O6.4H2O. The whole structure has

infinite helical chains of O-H-O hydrogen bonds between the molecules of

water of crystallization and the oxygen atoms of the anions (Beevers and

Hughes 1941 and Görbitz and Sagstuen 2008).

(iii) Powder X-ray diffraction analysis

The grown crystal of potassium sodium tartrate tetrahydrate was

finely powdered and subjected to powder XRD analysis using CuK radiation

of wavelength ( = 1.5418 Å). The obtained diffraction peaks (Figure 6.6)

are indexed with the help of powderX software package. The well defined

Bragg peaks at specific 2 angles show high crystallinity of the potassium

sodium tartrate tetrahydrate.

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Figure 6.6 Powder X-ray diffraction pattern of potassium sodium

tartrate tetrahydrate

(iv) High Resolution XRD (HRXRD)

To reveal the crystalline perfection of the specimen crystals, a

multicrystal X-ray diffractometer (MCD) was used to record diffraction

curves (DCs) (Lal and Bhagavannarayana 1989). The specimen crystal is

aligned in the (+,-,-,+) configuration. Figure 6.7 (a) shows the High

Resolution X-ray diffraction curve recorded for a typical potassium sodium

tartrate tetrahydrate (PST) single crystal specimen grown conventionally by

using (100) diffracting planes in symmetrical Bragg geometry by employing

the multicrystal X-ray diffractometer with MoK1 radiation. The solid line

(convoluted curve) is well fitted with the experimental points represented by

the filled rectangles.

On deconvolution of the diffraction curve, it is clear that the curve

contains three additional peaks, which are 60, 33 and 123 arc sec away from

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the main peak (close to the peak at zero position). These three additional

peaks correspond to three internal structural low and very low angle

boundaries (Bhagavannarayana et al 2005) whose tilt angles are 60, 33 and

90 arc sec from their adjoining regions. The FWHM of the different

boundaries are 22, 14, 62 and 55 arc sec. Though the specimen contains low

angle boundaries, the low FWHM values and the low angular spread of

around 300 arc sec (one twelfth of a degree) of the diffraction curve indicate

that the crystalline perfection is fairly good.

In SR method grown crystal, the solid line is well fitted with the

experimental points represented by the filled circles. On deconvolution of the

diffraction curve, it is clear that the curve contains two additional peaks,

which are 15 and 20 arc sec away from the central peak Figure 6.7 (b). These

two additional peaks correspond to two internal structural very low angle

boundaries whose tilt angles are 15 and 20 arc sec from their adjoining

regions. The FWHM of the boundaries are 65, 15 and 16 arc sec.

Figure 6.7 HRXRD pattern of potassium sodium tartrate tetrahydrate

by (a) slow evaporation solution growth technique (b) SR

method

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Though the crystal contains a low angle boundary, the low angular

spread of around 250 arc sec of the DC indicates that the quality of the crystal

is fairly good. It may be mentioned here that such a very low angle boundary

could be detected with well-resolved peak in the diffraction curve only

because of the high resolution of the multicrystal X-ray diffractometer used in

the present studies.

6.4.2 Optical Studies

The UV-Visible-NIR spectral analysis of PST shows the percentage

of transmittance and was compared between the conventional solution grown

and the SR method grown PST crystals. The SR method grown crystals of

PST was cut and polished to a thickness of 1 mm and subjected to optical

studies. It is inferred from the spectrum, that the SR grown crystal gives 75%

transmittance while that of conventional solution grown crystal gives 62% of

transmittance for the same thickness of 1mm. The graphical representation of

the % transmittance is shown in Figure 6.8. From the comparison the SR

grown crystal shows better transmittance than the conventional solution

grown crystal. Larger the transparency window more will be the practical

applicability. The difference in the percentage of transmission is due to the

ordered orientation in a particular plane. Since the conventional grown crystal

gets thermal effect from solution which induces defects, thereby reducing the

transmittance to 62%.

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Figure 6.8 UV-Vis-NIR spectrum of potassium sodium tartrate

tetrahydrate single crystal

6.4.3 FT-IR Spectrum

The recorded FT-IR spectrum of potassium sodium tartrate

tetrahydrate in the range 4000 - 400 cm−1 is shown in Figure 6.9. The peaks

corresponding to the stretching and bending of C-C bonds generally occur in

the very low frequency region (i.e., below 500 cm-1). The weak C-C

stretching vibration appears on the broad region of 1200-800 cm-1. The peaks

at 1082, 1118 and 890 cm-1 can be assigned to C-C stretching vibrations.

Carboxylic acid dimers display a very broad intense O-H stretching

absorption in the region of 3300-2500 cm-1 (Silverstein et al 1981). The peaks

at 2978, 2924 and 3271 cm-1 confirm the presence of carboxylic acid in the

crystal lattice. The conversion of the carboxylic acid to a salt is confirmed by

the presence of carboxylate anion structure in the lattice with the strong

asymmetrical stretching band at 1609 cm-1. The broad band in the higher

energy region between 3404 and 3510 cm-1 corresponds to the carboxylate

anion.

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Figure 6.9 FT-IR spectrum of potassium sodium tartrate tetrahydrate

6.4.4 Raman Spectral Studies

The Raman measurement of PST was carried out in a back

scattering geometry with incident light linearly polarized and unpolarized

scattered light was detected with a resolution of 0.3 cm-1. Excitation line at

632.8 nm was provided by air cooled He-Ne laser. The power at the laser

head was 10 mW, a lens of 50x was used in the microscope to give a spot size

of 3 m on the sample with a measurement time of 10 s. Figure 6.10 shows

the Raman spectrum of PST.

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Figure 6.10 Raman spectra of potassium sodium tartrate tetrahydrate,

inset figure showing Raman spectrum between

1200-1450 cm-1

The O-H stretching vibration gives a broad band about 3000 cm-1.

The fine structure is due to hydrogen bonding. The intensity is very low

because O-H bond is highly polar. O-H stretching makes much contribution to

its piezoelectric property. O-H is much distributed compared to the others due

to the hydrogen bonding interaction, so such a variation in interaction could

distort the electronic cloud much and hence such groups could be more

contributing to piezoelectric nature. The C-H vibration gives peaks at 2981

and 2930 cm-1. The peak at 2930 cm-1 is very much intense, as the less polar

C-H bond gives much distortion in electron cloud (polarizability). The C-H

bending mode occurs at 1353 cm-1. The broad peak at 1383 cm-1 is presented

at insert view, owing to symmetric COO- vibrations. Hence this group

interacts with other groups in the crystal. Because of its interaction this group

could also be a good contributor to piezoelectric property of the crystal. The

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C-O vibration gives its peak at 1072 cm-1 which is very sharp hence, less

interaction with the other groups in the crystal. These Raman spectral bands

are very much needed to identify groups that contribute piezoelectric effect.

The spontaneous electronic polarization is attributed to the movements of

hydrogen bonds (Wooster 1953).

6.4.5 Thermal Studies

The TG/DTA thermograms for powdered material of potassium

sodium tartrate tetrahydrate were recorded in nitrogen atmosphere with a

heating rate of 15C /min using STA 409PC instrument. The TGA

thermogram shown in Figure 6.11 (a) reveals three stages of decomposition in

potassium sodium tartrate tetrahydrate. The TGA trace appears nearly straight

up to its melting point showing the thermal stability of the grown crystal. The

melting and decomposition occur simultaneously. The first stage of

decomposition in DTA is due to the elimination of water molecule from the

crystal lattice. The second stage of decomposition is due to the evolution of

CO2 molecules from the crystal lattice due to breaking of tartrate bond which

is present in the PST compound. After decomposition the material has a

residue of 46.39 % which is shown in TG thermograms. From the DSC

spectrum in Figure 6.11 (b), a sharp melting point at 70C is observed which

shows a good degree of crystallinity of the grown ingot. The onset of the

decomposition of PST is observed at 118.1C and ends at 137.8C. The

stepwise decomposition implies the phase transition occurring in the

compound.

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Figure 6.11 (a) TG/DTA thermograms of potassium sodium tartrate

tetrahydrate (b) DSC curve of potassium sodium tartrate

tetrahydrate

6.4.6 Dielectric Studies

Good quality single crystals of PST of desired size were selected

for dielectric measurements. The main process that occurs in any dielectric

under the influence of electric field is polarization which refers to the limited

displacement of bound charges or orientation of dipoles. The dielectric

behaviour of the sample was studied at room temperature as mentioned in

section 1.11.6. The sample was electroded on either side with air-drying silver

paste, so that it behaved like a parallel plate capacitor. The studies were

carried out at room temperature for the frequencies varying from 50 Hz to

5 MHz. The sample was mounted in a specially designed two terminal sample

holder made of stainless steel. The most important result concerns the

determination of the role of hydrogen bonds in the appearance of the

spontaneous polarization (Prasad et al 1996).

The frequency dependence of the dielectric permittivity is shown in

Figure 6.12 (a). The dielectric permittivity was calculated using the relation as

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mentioned in Equation (1.8). Dielectric permittivity and dielectric loss

become nearly frequency independent, both these parameters gradually

decrease with increase in the applied frequency as shown in Figure 6.12 (b).

Due to electronic exchange of the number of ions in the crystal there is a local

displacement of electrons in the direction of the applied field, which in turn

gives rise to polarization.

As the frequency increases, a point will be reached where the space

charge is unable to sustain and comply with external field thereby decreasing

the polarization. The magnitude of dielectric permittivity depends on the

degree of polarization and charge displacement in the crystals

(Dharmaprakash and Mohan Rao 1989). The dielectric permittivity of

materials is due to the contribution of electronic, ionic, dipolar and space

charge polarizations which depend on the frequencies. At low frequencies, all

these polarizations are active. The space charge polarization is generally

active at lower frequencies (Smyth 1965). The variation of capacitance with

frequency is depicted in Figure 6.12 (c), it is observed that the capacitance

decreases with increase in frequency and this is due to charge redistribution.

At low frequency the residual charges more readily redistribute to

the positive side of the applied field and become negatively charged, while

the residue close to the negative side of the applied field becomes positively

charged since the capacitance of the parallel plate capacitor is inversely

proportional to the applied electric field. As the frequency increases the

capacitance decreases and the charges no longer have time to rearrange in

response to the applied voltage (Vasudevan et al 1998).

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Figure 6.12 (a) Dependence of dieletric permittivity with log frequency

(b) Variation of dielectric loss with log frequency

(c) Capacitance with log frequency

6.4.7 Mechanical Properties

The Vickers microhardness test at room temperature with the load

ranging from 10-70 g with an indentation time of 3 sec on PST crystal was

carried out on (100) plane. The hardness number was calculated using the

relation given in Equation 1.7.

The schematic (Figure 6.13) representation of indentation size

effect (ISE) has been shown below. Hardness decreases on increasing the

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applied load, which is called as load dependent hardness region. On the other

hand the plot shows a straight line which indicates the load independent

hardness region.

Figure 6.13 Schematic representation of ISE behaviour

Figure 6.14 (a and b) shows the profile of hardness number with

load and work hardening coefficient. It is observed that the hardness number

increases with increasing load. From this graph it is seen that the grown PST

crystal exhibits reverse indentation size effect that is, increase in hardness

value with increasing load. ISE is caused by the generation of cracks around

indentation. In contrast to the above normal ISE, a reverse type of indentation

size effect, where the apparent microhardness increases with increasing

applied test load (Mythili et al 2007).

The work hardening coefficient (n) of the material was calculated

using the Meyer's relation. The plot of log P with log d is shown in

Figure 6.14 (b). In this present investigation, the work hardening coefficient n

is found to be 1.7 by the least squares fitting method.

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Figure 6.14 (a) Dependence of Vickers Hardness Number with load

(b) log P vs log d (SR grown crystal)

The stiffness constant gives an idea about the nature of bonding

between neighboring atoms (Sharma et al 1999 and Rani Christhu Dhas

1994). This is the property of the material by virtue of which it can absorb

maximum energy before fracture occurs (Wooster 1953). For various loads

the elastic stiffness constant is calculated using Wooster’s empirical relation

(2.3). The variation of stiffness constant and yield strength plotted with load is

shown in Figure 6.15 (a and b).

If n > 1.6 the material belongs to soft material category (Onitsch

1956) hence, PST is moderately hard. Figure 6.15 (b) shows the plot of load

dependent yield strength. The indentation impressions are associated with

cracks at all loads on (100) planes of the crystal. However, the cracks are well

defined beyond a load of 50 g. The formation of radial-median and Palmqvist

crack occurs as a result of indentation. If c/a 2.5 for which we get median

cracks, ‘a’ being the length of the half-diagonal of the indent. For c/a 2.5,

we get palmqvist or radial cracks type, where c is crack length and a is half

diagonal length of the indendation (Proton and Rawlings 1989 and

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Bamzai et al 1998). For the grown SR method PST crystal palmqvist crack

has been observed. The mechanical data are given in Table 6.2.

Figure 6.15 (a) Dependence of stiffness constant with load (b) Variation

of yield strength with load (c) Indentation mark on the

surface of PST crystal

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Table 6.2 Hardness data of SR method grown PST crystal in (100)

Load P (g)

Hardness number Hv (kg mm-2)

Crack length

c (m) c/a Nature of cracks

10 9.4 - - -

20 17.8 83.7 1.85 Palmquist

30 32.8 - - -

40 50.3 71 1.94 Palmquist

50 69.2 73.4 1.90 Palmquist

60 65.87 76.71 1.96 Palmquist

6.4.8 Laser Damage Threshold

The laser damage threshold (LDT) studies were carried out for

conventional grown crystal and SR grown crystal in (100) plane using a

Nd: YAG (1064 nm) laser for a pulse width of 10 ns and a pulse duration of

15 s. Both crystals were exposed to laser beam on the (100) plane. The output

of the laser beam was controlled by an attenuator and the beam is allowed to

pass through a converging lens. The lens with a focal length of 10 cm was

used. The diameter of the beam spot on the sample was 1mm. During laser

irradiation on varying the energy density of the input laser beam for which the

laser beam damages the sample surface (Gong 2000). On increasing the input

energy the surface of the sample gets damaged, at first pitting occurs followed

by crack formation, which leads to the occurrence of catastrophic damage,

when the fluence level was 50 mJ/cm2 and 59 mJ/cm2 for conventional grown

and SR grown PST crystals, respectively. Table 6.3 shows the observation of

damage over the surface with increasing power

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During laser irradiation, localized heating due to absorption by the

inclusion results in its vaporization, followed by damage to the crystal

through local melting as well as fracture from thermal stresses (Montgomery

and Milanovich 1990 and Nakatani et al 1988). Apart from thermal effect,

multi photon ionization may be the reason for the damage of the surface due

to laser irradiation. Laser damage threshold values are found to be

6.4 GWcm-2 and 8.3 GWcm-2 respectively for conventional grown and SR

method grown PST single crystals. The SR method grown crystal shows high

laser damage threshold when compared to slow evaporation solution grown

crystal. Figure 6.16 (a and b) depicts the micrograph image of LDT for the

conventional grown crystal and SR crystals. The reason may be the SR

method grown has lesser defects than the SEST grown crystals. The

crystalline perfection is good for SR grown sample when compared to SEST

grown crystal. The high damage threshold shows the availability of the

material for its practical applications. Table 6.4 illustrates the comparison of

laser damage threshold values for tartrates.

Table 6.3 The observation of damage on the surface with increasing

laser power

SR grown PST

Energy (mJ)

SEST grown PST

Energy (mJ) Observation

22.8 29.7

No change 25 31.4

31.3 38.4

38 41 Damage starts

46.9 45 Pitting occurs

59 50 Crack occurs

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Figure 6.16 Micrograph images of Laser damage threshold for

(a) conventional grown (100) plane of PST (b) SR method grown (100) plane of PST

Table 6.4 Comparision of Laser damage threshold values for tartrates

Compound Laser Damage Thershold (GW/cm2)

L-Tartaric acid 5.4 (Martin Britto Dhas et al 2007)

L-Prolinium tartrate 5.9 (Martin Britto Dhas and Natarajan 2007)

PST - SEST 6.4 (Present work)

PST - SR 8.3 (Present work)

6.4.9 Factor Group Analysis

The factor group and site group are taken into consideration in

group theoretical analysis. The compound potassium sodium tartrate

tetrahydrate (PST) crystallizes in the noncentrosymmetric space group P21212

( 32D ) of orthorhombic system. The factor group analysis of PST crystal was

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carried out using the character table for the point group C1(4). The primitive

unit cell contains four molecules (Z = 4). A single molecule possesses

28 atoms which gives rise to 112 atoms in a unit cell. By applying the group

theory concept the fundamental modes of potassium sodium tartrate

tetrahydrate crystal were explored as 333 vibrational optical modes which

decomposes into 333 = 84 A + 83 B1 + 83 B2 + 83 B3 and (B1 + B2 + B3) are

the acoustics modes. Factor group analysis was performed by following the

correlation scheme outlined by Rousseau et al (1981). The results are

presented in Table 6.5. The polarizability tensors are depicted along the

crystallographic X, Y and Z axes.

The vibrations can also be determined by recording Raman spectra

and infra red spectra. The molecular structure of PST consists of C-C, C-O,

C=O and O-H. The predicted vibrations of PST could be due to lattice

vibrations and internal vibrations. The fundamental mode reveals

336 vibrations which can be attributed as 84 A + 83 B1 + 83 B2 + 83 B3 and

21 external modes contributed by 9 translational (3 B1 + 3 B2 + 3 B3),

12 rotational (4 B1 + 4 B2 + 4 B3) modes. The correlation scheme obtained is

presented in Table 6.6. Each internal mode splits into four components of

which B1 (xy), B2 (xz), B3 (yz) and A (xx, yy , zz) are Raman active and

all B1 (Z), B2 (Y) and B3 (X) are IR active.

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Table 6.5 Factor group analysis - Summary

D2

symmetery

C1 site symmetery K Na C H O

Opical

mode

Acoustical

mode Total

Internal External

A - 78 3 3 12 36 30 84 0 84

B1 3T, 4R 78 3 3 12 36 30 84 1 83

B2 3T, 4R 78 3 3 12 36 30 84 1 83

B3 3T, 4R 78 3 3 12 36 30 84 1 83

Total 9T,12R 312 12 12 48 144 120 336 3 333

Table 6.6 Correlation scheme of potassium sodium tartrate

tetrahydrate

Site Symmetry Factor group

symmetry

Activity

Raman IR

84 A xx, yy, zz

xy

xz

yz

-

Z

Y

X

A333 83 B1

83 B2

83 B3

6.5 CONCLUSION

Good quality single crystals of potassium sodium tartrate

tetrahydrate were grown by the unidirectional growth method of

Sankaranarayanan-Ramasamy and conventional solution growth method. The

single crystal as well as powder X-ray diffraction analyses show that PST

crystallizes in orthorhombic system. The structural perfection of the grown

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single crystals was studied by HRXRD. The functional groups were

confirmed by FT-IR and Raman spectral studies. The thermal behaviour of

the grown crystal was studied by TG/DTA and DSC. The UV-Visible study

implies the optical quality of the SR grown PST crystals is better than that of

SEST grown crystals. The dielectric permittivity is high in the case of SR

grown crystal when compared to the SEST grown crystal. The hardness value

of PST crystal is greater for SR grown crystal and withstands load up to 60 g,

above which cracks were observed. From the mechanical measurements

stiffness constant and yield strength were evaluated. The laser damage

threshold (higher value) of the SR grown PST single crystal indicates that the

crystal has lesser defects. The unidirectional grown crystals possess good

optical, mechanical, dielectric and structural perfection.