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Front Title

Raman, C V

A New Radiation

Indian J. Phys. 82 (9), 1101-1102 (2008) 
JQMkHALv 
or w&mWBwS& 
Vol. 82 • No. 9 • September 2008 
cpc ONTENTS 
Special Issue on "Electrodynamics of Classical Charged Particles'9 
Front Title 1095 
Advisory Board and Editors 1097-1098 
From Editor's Desk 1099 
Front Contents 1101-1102 
Foreword 
JOSE LUIZ LOPEZ-BONILLA 1103 
Hidden symmetries of the motion of a charged particle in a uniform 
magnetic field 
G F TORRES DEL CASTILLO 1105-1112 
The significance of the Schott energy in the electrodynamics of 
charged particles and their fields 
E ERIKSEN AND 0 GR<|>N 1113-1137 
Two-body problem with retarded interactions and radiation reaction 
in classical electrodynamics 
YURIJ YAREMKO 1139-1158 
Proper-time foundations for classical electrodynamics 
TEPPER L GILL AND WOODFORD W ZACHARY 1159-1178 
[ Cont'd, on next page J 
1102 Contents 
A deduction of the Landau-Lifshitz equation of motion without mass 
renormalization in classical electrodynamics 
G ARES DE PARGA, M ORTIZ-DOMINGUEZ AND R MARES 1179-1189 
Electromagnetic mass model admitting conformal motion 
SAIBAL RAY, A A USMANI, F RAHAMAN, M KAUM AND K CHAKRABORTY 1191-1204 
Expanding the realm of'classical' electrodynamics 
CYNTHIA KOLB WHITNEY 1205-1218 
Forthcoming Publications 1219-1220 
Notes for Contributors 1221-1224 
Our Special Publications 1225-1226 
RenewalNotice-2009 1227 
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Front Contents

Indian J PhysM(% 1221-1224 (2008) 
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Notes for Contributors

Singh, Sunita

Raj, Deo

Elastic Cross Section for Electron Scattering by N2O Molecule

Ganesh, V

Rao, K Kishan

Indian!.Phys. 82(10) 1293-1300(2008) 
Surface and hardness studies on as-grown {100} faces of 
zinc (tris) thiourea sulphate crystals 
V Ganesh and K Kishan Rao* 
Department of Physics, Kakatiya University, Warangal-506 009, Andhra Pradesh, India 
E-mail : kisriarikotte@yahoaco.in 
Received 13 November 2007, accepted 13 June 2008 
Abstract : Single crystals of zinc (tris) thiourea sulphate are grown at 30°C by slow evaporation method. 
Surface studies have been carried out on a number of {100} faces of these crystals. Typical striations are 
observed on these faces, mostly they are oriented parallel to shorter face of the crystals. In very few cases 
striations parallel to the longer face are also observed. These studies suggest that the growth occurs by 2D 
nucleation. Further chemical etching technique has been employed to study dislocations in these crystals. The 
dislocations are randomly distributed, they are mainly observed at the edges of the crystal. The average 
dislocation density is about 4 x ID^/cm2. Mechanical characterization has been done by Vicker's microhardness 
technique. The work-hardening index number (n) for these crystals is about 1.9 which is close to theoretically 
expected value of 2. The hardness studies made on about 50 crystals suggest that hardness (Hv) value is about 
76 ±1 kg/mm2. 
Keywords : Surface studies, etching, microhardness. 
PACS Noa. : 81.10.Dn, 61.72.Ff, 62.20.Qp 
1. Introduction 
It is well known that some organic crystals are flood NLO materials but their 
applications are limited due to their poor mechanical properties, whereas inorganic NLO 
materials show good mechanical and thermal properties but posses modest optical 
nonlinearities. To solve this problem work has been initiated on the growth of semi-
organic NLO materials [1-3]. Zinc (tris) thiourea sulphate (ZTS) is one such material 
belongs to the family of semi-organic nonlinear optical (NLO) materials. These crystals 
can be grown comfortably from solution at moderate temperatures. They crystallize in 
the non-centrosymmetric orthorhombic with space group Pca2y (point group mm2). The 
•attice parameters are reported to be a * 11.26 A, b * 7.73 A, c * 5.491 A [4]. ZTS 
w 
,c
°n«8pondino Author ©2008 I ACS 
1294 VGaneshandKKishanRao 
crystal has drawn considerable interest as a potential material for second harmonic 
generation (SHG) where SHG efficiency is 1.2 times that of KDP and it is used as 
a potential material for the use as electro-optic modulator also [3]. Venkataramanan 
and co-workers [5] studied the effect of laser damage in ZTS at a wavelength of 1064 
nm and 532 nm using Nd : YAG laser, they observed that ZTS has laser damage 
threshold of the order of Gw/cm2 which is comparable to NLO crystals such as KTP 
and BBO. Due to its importance, it has attracted many people but most of the work 
has been confined to its growth, spectral and thermal analysis studies only [1]. 
Systematic study is lacking on surface studies, dislocations and hardness of these 
crystals. These studies are important because they (surface studies) help in understanding 
the possible growth mechanism of these crystals, dislocations and hardness studies 
help in understanding the strength of the crystals. In view of this we have undertaken 
growth of ZTS crystals, particularly attention has been focused on the systematic study 
of as-grown faces of these crystals, dislocations and microhardness. 
2. Experimental 
Zinc (tris) sulphate (ZTS) was synthesized at 30°C by dissolving 3 : 1 ratio of thiourea 
and zinc sulphate in water [1]. 
ZnS04 + 3CS(NH2)2 -+ Zn[CS(NH2)2]3S04 
The solution was thoroughly stirred using a magnetic stirrer and white crystalline ZTS 
was formed, the synthesized substance was purified by repeated recrystallization 
process. The saturated solution of ZTS was prepared using deionized double distilled 
water at 30°C. The solution was continuously stirred at least for one hour to ensure 
concentration over the entire volume of the solution. Now the solution is transferred to 
a constant temperature bath of accuracy ±0.1 °C. Initially the temperature of the solution 
was raised to 35°C and slowly brought back to 30°C in a period of 3 to 4 hours. Now 
the solution was allowed for very slow evaporation. Crystals of good quality of size 1 
cm along one edge were obtained in a period of three weeks. Chemical etching 
technique was employed to study dislocations in these crystals. Microhardness 
measurements were made using Leitz-Wetzlar hardness tester fitted with a Vicker's 
diamond indenter. Hardness values (Hv) are calculated from the expression 
Hv « 1.854 P/d2 kg/mm2 
where P is the load applied in g and d the diagonal length in ft. Each value is atleast 
the average of four dose measurements. 
3. Results and discussion 
3.1. Crystal growth and surface studies : 
Figure 1(a) shows the crystals of ZTS grown from its aqueous solution. These crystals 
are essentially bounded by {100}, {010}v {001} and {012} faces as shown by line 
Surface and hardness studies on as-grown {100} faces of zinc (iris) thiourea sulphate crystals 1295 
diagram (Figure 1(b)). In all these crystals {100} and {010} faces grew larger than other 
faces. The observed morphology of these crystals is similar to that reported earlier 
[1,3]. 
{001} 
{010} 
Figure 1(a). As-grown crystals of ZTS (m x 1.2). 
^magnification 
Figure 1(b). Line diagram of ZTS crystal. 
{100} 
It is well known that when the as-grown crystals, particularly from solution grown 
observed under a good reflection microscope reveal some typical growth features. They 
include growth spirals, hillocks, overgrowths, striations etc. These are not only 
interesting to see but help in understanding the growth mechanism of the crystals. In 
view of this an attempt has been made to understand the growth process of these 
crystals, for which at least 30 as-grown crystals are studied under reflection microscope. 
{100} faces grow to a considerable size, hence, the studies are confined to these faces 
only. Most of these faces reveal typical striations (Figure 2(a)), which are parallel to 
the shorter edge of the crystal. It is important to mention that the striations do not 
propagate continuously from one end to other. Mostly they appear at the edges and 
progress towards the center but after propagating to some extent they become 
diffusing. In few cases the striations appeared paraltel to longer faces also (Figure 2(b)). 
(a) (b) 
Figure 2. Typical striations on as-grown {100} face of ZTS crystals (m x 100). 
(a) Parallel to shorter face (m x 100) and (b) Parallel to longer face (m x 100). 
#n>-magnification 
1296 VGaneshandKKishanRao 
Sangwal [6] pointed out that the cause of the striations could be due to fluctuations 
in growth conditions such as sudden changes in temperature, cooling rate, convection 
of the solution or melt and concluded that these features are mostly due two 
dimensional growth mechanism. Prasad [7] also attributed different types of striations 
observed on FeS2 crystals to two dimensional (2D) growth nucleation. In the present 
studies we have not observed any growth spirals except striations. These studies 
suggest that these crystals appear to grow by 2D growth process, particularly by layer 
growth mechanism. Further the observation of striations at the edges suggests that the 
growth process initiates at the edges and spreads towards the center. 
Figure 3(a) shows a thin overgrowth on {100} face of ZTS crystals, it is 
interesting to note that some typical interlaced pattern are observed on this flake. Van 
Enckevort and Jetten [8] observed some typical growth steps on {010} face of KAP 
crystals. From their sophisticated microscopic studies pointed out that they originate 
from two growth centers, which were observed to be screw dislocation sources. Prasad 
[9] observed interlaced step pattern on n-pentadecanoic acid crystals, attributed the 
spreading of these steps to as due to screw dislocations or 2D growth mechanism. 
In the present work the crystals are grown by slow evaporation method. Therefore the 
supersaturation normally is higher than the spiral growth range, hence it is felt that 
screw dislocation mechanism may not be responsible for the formation of steps. The 
reason for the formation of interlacing steps appears to be due to nucleation and 
propagation of steps (Figure 3(b)) from two 2D sources (S,, ^ ) once they interact with 
each other form interlacing patterns. Figure 3c shows etch pattern on and around the 
overgrowth the distribution of etch pits is random. 
3.2. Chemical etching : 
Chemical etching technique has been employed to study dislocations in these crystals. 
In view of the meager information on etching studies on these crystals [10,5], a 
number of etchants were tried (Table 1). Good etching action was observed by the 
mixture of 1 part of acetic acid + 2 parts of formic acid the etching time is about 20 
sec. Figure 4(a) shows etch pattern observed with this etchant on {100} faces of ZTS 
crystal, the etch pits are more or less rectangular in shape, the longer sides of the 
etch pits are parallel to shorter face of the crystals. Figure (4b and 4c) shows the 
successive etch pattern photographs on ZTS, the etching timings are 20 sec and 30 
sec. It can be seen from these photographs that all the etch pits of Figure 4(b) persist 
in 4(c) with increase in size indicating that etch pits are formed at the sites of 
dislocations only. The distribution of pits is not uniform, it is more at the edges than 
at other regions. The average density of dislocations is about 4 x 105/cm2. 
3.3. Microhardness studies : 
Hardness is an important solid state property depends on different parameters such as 
Surface and hardness studies on as-grown {100} faces of zinc (tris) thiourea sulphate crystals 1297 
Figure 3(c). Etch pit pattern observed on and around of overgrowth of ZTS Crystal (m x 100). 
*m-magnification 
Table 1. Action of various etchants on crystal surface of ZTS. 
Etchant 
(1) Methanol 
(2) Ethanol 
(3) Water 
(4) Acetic acid 
(5) Formic acid 
(6) Acetic + Formic acid (1 
(7) Acetic + Formic acid (1 
(8) Acetic + Formic acid (1 
:2) 
:3) 
:4) 
Crystal face 
{100) 
{100} 
{100} 
{100} 
{100} 
{100} 
{100} 
{100} 
Action 
No etching action 
No etching action 
Polishing action 
No etching action 
No etching action 
Well-defined etch pits 
Etching action increases 
Etching action increases and surface becomes rough 
interatomic spacing, lattice energy, Debye temperature, elastic constants etc. The 
microhardness technique is a rapid and nondestructive method to study deformation of 
crystals. The variation of Hv with load ranging from 10 g to 120 g is illustrated in 
figure 6. It is evident from this Figure that the Hv value increases initially up to a load 
1298 VGaneshandKKishanRao 
Figure 4. Etch pit pattern observed on {100} face of ZTS crystal. 
(a) Etched with acetic + formic acid (1 : 2) (e.t 20 sec) (m x 100), 
(b) Successive etch pattern after 20 sec (m x 100) and 
(c) Successive etch pattern after 30 sec (m x 100). 
*m-magnification 
of 60 g and later it becomes load independent. Similar increase in Hv with load was 
observed on these crystals [1], but this work was limited to 50 g only. In general, load 
dependence of hardness is expected to be more at lower loads and decreases as the 
load increases, finally it becomes load independent. This statement appears to be true 
for simple materials like metals, ionic solids etc. where they are mostly mono, di 
atomic systems [11,12] and in these samples the size of indenter impression increases 
uniformly with load and produces clear impressions also. The reason for this has been 
attributed to (i) as the indenter lands on crystal surface under a particular load, the 
material around it is displaced smoothly [13] and (ii) it could be due to the active 
participation of slip systems which help in easy glide of the material In ZTS crystals 
the atomic arrangement is complex therefore the gliding may not be simple, hence it 
appears that some kind of reorientation of some of these molecules may take place 
during indentation process. This could be a reason for showing initial decreases in size 
Surface and hardness studies on as-grown {100} faces of zinc (tris) thiourea sulphate crystals 1299 
85-
8^ 
75-
701 
C I 20 40 60 
, ^ | r—4) 
{100} ZTS 
80 100 120 4.5 
Figure 6. Plots of log P against log d for ZTS 
crystal. 
p(grams) 
Figure 5. Load variation of hardness for {100} face of 
ZTS crystal. 
of impression, which causes an increase in hardness with increasing load. As the load 
reaches an optimum value about 60 g, some kind of proper alignment appears to take 
place inside the material thus leading to load independent value above this load. The 
present load independent hardness value is 78 kg/mm2, which is close to the value 
of 82 kg/mm2 [14]. 
3.4. log P against log d plots : 
The load variation can be interpreted by using Meyer's law P = acf\ where 'P* is the 
load applied, 'of* is the diagonal length of impression, 'a1 and 'n' are constants. Figure 
7 shows the variation of log P against log d for these crystals. From the slope the 
value of '/?• has been estimated, it turns out to be 1.9 which is close to 2 as 
66-68 68-70 70-72 72-74 74-76 76-78 78-80 
Hardness 
Figure 7. Histogram showing variation of hardness for ZTS crystal. 
1300 VGanesh and K Kishan Rao 
theoretically expected, this is called as Meyer's index number or work-hardening index 
also. It has been observed in this laboratory that unlike melt grown crystals, solution 
grown crystals such as alums, NaCI03, NaBr03, alkaline earth nitrates, ADP and KDp 
etc. have shown considerable variation in hardness value, even in the crystals grown 
in the same crop [15-17]. In order to understand this indentation studies have been 
carried out atleast on about 50 ZTS crystals in the load independent region [p = 75 
g], the hardness data is shown by histogram (Figure 8). It can be noticed from this 
diagram that maximum hardness value varies from 76 kg/mm2 to 78 kg/mm2 
suggesting that this is the most possible value for these crystals. 
4. Conclusions 
(i) Typical oriented striations are observed on {100} faces of ZTS crystals suggesting 
that the growth appears to be due to 2D mechanism, 
(ii) 1 : 2 parts of acetic and formic acids mixture acts as good etching agent to 
reveal dislocations in these crystals, 
(iii) The microhardness study shows typical increase in hardness and reaches a load 
independent value of 76 ± 1 kg/mm2. 
Acknowledgment 
The authors are grateful to referees for useful suggestions. 
References 
[1] J Ramajothi, S Dhanuskodi and K Nagarajan Cryst Res. Techno!. 39 414 (2004) 
[2] Sunil Verma, M K Singh, V K Wadhawan and C H Suresh Pramana-J. Phys. 54 879 (2000) 
[3] Q Arunmozhi, E d e M Gomes and S Ganesamoorthy Cryst Res. Technoi. 39 408 (2004) 
[4] G O Andereeti, L Cavalca and A Musatti Acta Crystllogr. B24 683 (1968) 
[5] V Venkataramanan, C K Subramanian and H L Bhat J. Appl.Phys. 77 11 (1995) 
[6] K Sangwal Prog. Cryst. Res. Technoi. 19 237 (1989) 
[7] P B V Prasad Cryst. Res. Technoi. 21 537 (1986) 
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(1982) 
[9] P B V Prasad Cryst. Res.Technol. 23K 93 (1988) 
[10] V Venkataramanan, G Dhanraj, V K Wadhawan, J N Sherwood and H I Bhat J. Cryst. Growth 154 92 
(1995) 
[11] B W Mott Micro-indentation Hardness testing (London : Butter Worths) p206 (1956) 
[12] K J Pratap and V Hari Babu Bull. Mater. Sci. 2 43 (1980) 
[13] Yu S Boyarskaya, S S Shutova and HP Zhitaru Phys. Status Solid! 30 K7 (1975) 
[14] S S Gupte and C F Desal Cryst. Res. Technoi, 34 1329 (1999) 
[15] K Kishan Rao. V Surender and B Saritha Rani Bull. Mater. Sci. 25 641 (2002) 
[16] P V Raja Shekar, V Gartesh and K Kishan Rao Bull. Mater. Sci. (communicated) (2007) 
[17] V Ganesh and K Kishan Rao Indian J. Phys. (communicated) (2007) 


Surface and Hardness Studies on As-Grown {100} Faces of Zinc (Tris) Thiourea Sulphate Crystals

Anbarasan, P M

Meenakshi, G

Jeyapriya, K

Subramanian, M K

Subramani, K

Growth, Structural and Optical Studies on Organic Single Crystal Imidazole

Mishra, A P

Mishra, V K

Tripathi, Roopali

Mishra, B N

Heliographic Distribution of X-Ray Solar Flares and their Association with Geomagnetic Disturbances in Relation to Solar Radio Emissions and Coronal Mass Ejections

From Editor's Desk

Srivastava, S K

Kar, Manoranjan

Ravi, S

Preparation, Characterization and Magnetic Properties of Hexagonal Y1-xCexMnO3

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Front Title

A New Radiation

Front Contents

Notes for Contributors

Elastic Cross Section for Electron Scattering by N<SUB>2</SUB>O Molecule

Surface and Hardness Studies on As-Grown {100} Faces of Zinc (Tris) Thiourea Sulphate Crystals

Growth, Structural and Optical Studies on Organic Single Crystal Imidazole

Heliographic Distribution of X-Ray Solar Flares and their Association with Geomagnetic Disturbances in Relation to Solar Radio Emissions and Coronal Mass Ejections

From Editor's Desk

Preparation, Characterization and Magnetic Properties of Hexagonal Y<SUB>1-x</SUB>Ce<SUB>x</SUB>MnO<SUB>3</SUB>

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