Thermal and Mechanical Properties of KDP-ADP Mixed Crystals Added with Glycine

Thermal and Mechanical Properties of KDP-ADP Mixed Crystals Added with Glycine

V. Rajalekshmi1 and

1Physics Research Centre, S.T.Hindu College, Nagercoil-629002,

Tamilnadu State, India

C. K. Mahadevan2

2Center for Scientific and Applied Research, PSN College of Engineering and Technology, Tirunelveli-627152,

Tamilnadu State, India

Abstract – Pure and glycine added (in two different concentrations, viz. 0.005 and 0.010 M) K1-x(NH4)xH2PO4 (with x = 0.0, 0.25. 0.5, 0.75 and 1.0) single crystals (a total of

1. have been grown and characterized thermally and mechanically. The crystals were grown by the free evaporation of solvent at room temperature. Thermogravimetric (TGA) measurement was carried out in the temperature range 30-700 oC for the five pure mixed crystals only expecting that small amount of glycine addition may not affect the thermal stability much. Vickers microhardness measurements were carried out on the {100} face of all the 15 crystals grown and various mechanical parameters were evaluated to understand the mechanical strength of the crystals. Results obtained indicate that the crystal with the middle mixed composition exhibits more thermal stability. Further, it is found that the pure and glycine added mixed crystals grown in the present study belong to hard materials category.

   Keywords: Crystal growth from solution, KDPADP mixed crystals, Glycine doped crystals, Thermal properties, Mechanical properties.

   1. INTRODUCTION

      KDP (KH2PO4, potassium dihydrogen phosphate) and ADP (NH4H2PO4, ammonium dihydrogen phosphate) single crystals have drawn special attention of research workers due to their importance and interesting properties for more than six decades in the past. Both are isomorphous to each other and belong to the tetragonal crystal system at room temperature.

      For many emerging technologies, it is necessary to form hybrid materials (by doping or forming mixed crystals) with improved physical properties. The mixed composition/impurity concentration dependence, on forming hybrid materials, may vary significantly from system to system and from property to property. In some cases, these dependences may be highly nonlinear and the magnitude of the physical property may vary significantly from those of the pure (end member) ones.

      Several researchers have grown and characterized pure, impurity added and mixed crystals of KDP and ADP and reported several interesting results [1-15]. In principle, the system KDP-ADP forms a series of solid solutions over the whole range of compositions. However, earlier authors

      have found it difficult to grow bulk single crystals from all compositions [14]. It was ascribed to the development of internal stress due to the strong chemical bonding interaction between K+ and H2PO4- ions and the competitive growth of NH4+ and K+ ions affects the quality and morphology of the crystal.

      Aiming at discovering new materials, Mahadevan and his co-workers have planned and executed a research program on the growth and characterization of hybrid single crystals based on KDP and ADP. Several useful results have already been reported [16-26]. As a part of the above program, we have grown by the free evaporation of solvent method at room temperature and characterized glycine (a simple but important organic nonlinear optical material) added (0.005 and 0.010 M are the concentrations considered) mixed crystals of KDP and ADP [K1- x(NH4)xH2PO4 with x = 0.0, 0.25. 0.5, 0.75 and 1.0]. The

      structural and optical properties have already been reported [27]. Herein, we report the thermal and mechanical properties.

   2. MATERIALS AND METHODS

      Analytical reagent (AR) grade samples of KDP, ADP and glycine were used as the precursors. Double distilled water was used as the solvent. The single crystals were grown as we have reported earlier [27].

      It was expected that the small amount of glycine addition might not have modified significantly the thermal properties of K1-x(NH4)xH2PO4. So, the five undoped crystals grown were subjected to thermogravimetric(TGA) measurement. A thermal analyzer (model SDT Q600) was used for the purpose and the measurements were carried out in nitrogen atmosphere in the temperature range 30 700 at a heating rate of 10 /min. In order to characterize mechanically, all the fifteen crystals grown were subjected to Vickers microhardness measurement on the {100} face using a SHIMADZU HMV 2T microhardness tester with a diamond indenter. The diagonals of the indentations made (d) along with the crack length (c) were measured for three different loads (25, 50 and 100 g) in each case. The measurement was repeated at different places on the same surface of the crystal and the average values were considered. Various mechanical parameters were also evaluated.

   3. RESULTS AND DISCUSSION

3.1 Crystals Grown

All the fifteen crystals grown are found to be stable in atmospheric air, colorless and transparent. The single crystals grown in the present study can be represented as

KA1 K (1-x) (NH4)xH2PO4 with x = 0.0 (Pure KDP) KA2 K (1-x) (NH4)xH2PO4with x = 0.25

KA3 K (NH ) H PO with x = 0.50

KA1

KA1

13.5

Weight (mg)

Weight (mg)

13.0

12.5

12.0

11.5

22.0

21.5

KA2

KA2

Weight (mg)

Weight (mg)

21.0

20.5

20.0

19.5

19.0

18.5

(1-x)

4 x 2

4 0 200 400 600 800

0 200 400 600 800

KA4 K (1-x) (NH4)xH2PO4with x = 0.75

KA5 K (1-x) (NH4)xH2PO4with x = 1.0 (Pure ADP)

KA6 KA1added with 0.005M glycine KA7 KA2added with 0.005M glycine KA8 KA3added with 0.005M glycine KA9 KA4added with0.005M glycine KA10 KA5added with 0.005M glycine KA11 KA1 added with 0.010M glycine KA12 KA2 added with 0.010M glycine KA13 KA3 added with 0.010M glycine KA14 KA4 added with 0.010M glycine KA15 KA5 added with 0.010M glycine

105

100

Weight (mg)

Weight (mg)

95

90

85

80

75

70

65

Temperature (C)

KA3

KA3

0 200 400 600 800

Temperature C

11.5

11.0

Weight (mg)

Weight (mg)

10.5

10.0

9.5

9.0

8.5

Temperature (C)

0 200 400 600

KA4

KA4

Temperature (C)

The chemical compositions observed through density measurement for the mixed crystals, viz. KA2, KA3 and KA4 are K0.84(NH4)0.16H2PO4, K0.66(NH4)0.34H2PO4 and

K0.54(NH4)0.46H2PO4 respectively and all these fifteen crystals are found to be nonlinear optically active and significantly exhibit second harmonic generation [27].

1. Thermal properties

   Figure 1 shows the TGA patterns observed for the undoped crystals grown in the present study. Absence of weight loss observed around 100oC indicates the absence of water of crystallization in the molecular structure. The major weight loss occurs (see the TGA patterns in Figure 1) due to decomposition before melting for all the five crystals considered in the present study. The temperatures of this decomposition observed for KA1, KA2, KA3, KA4 and KA5 are 281.32, 282.6, 201.72, 252.5 and 207oC

   respectively. It should be noted that the decomposition rate with temperature decreases with the increase in ammonium content in the crystal. Further, KA3 [K0.5(NH4)0.5H2PO4 in the solution used for crystallization] is found to be thermally less stable. The thermal stability observed for pure KDP and ADP crystals is in agrement with that reported in the literature [14, 25, 26 ].

   KA5

   KA5

   10

   Weight (mg)

   Weight (mg)

   9

   8

   7

   6

   5 0 200 400 600

   Temperature (C)

   Fig -1: The TGA patterns observed for the KA1, KA2, KA3, KA4 and KA5 crystals

   The weight losses observed in the present study for KDP and ADP crystals are almost similar to those reported earlier[14]. So, the decompositions can be considered in a similar way in accordance with the following relations (s and g represent solid and gas respectively):

   For ADP,

   2NH4H2PO4 (s) >2NH3 (g) + 3H2O (g) + P2O5 (s) For KDP,

   KH2PO4 (s) > KPO3 (s) + H2O (g)

   For the mixed crystals, the decomposition takes place as evaporation of water and then ammonia. The ammonia evaporation is found to increase with the increase in ammonium content of the crystal.

2. Mechanical properties

The hardness of a material is a measure of its resistance it offers to local deformations [26].The micro-indentation test is a useful method for studying the nature of plastic flow and its influence on the deformation of the materials. Higher hardness value of a crystal indicates that greater stress is required to create dislocation [26]. The values of d (average diagonal of the indentation made) and c (crack length) observed in the present study are provided in Table 1.

Table -1: The measured d and c values

1.85

KA1

1.9

1.80 KA2

KA6

1.75 KA3

1.8 KA7

KA4 KA8

log d

log d

1.70

1.65

1.60

1.55

1.50

KA5

log d

log d

1.7

1.6

1.5

1.4

KA9

KA10

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

log p

1.85

1.80 KA11 KA12

1.75 KA13

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

log p

1.70

log d

log d

1.65

1.60

1.55

1.50

1.45

KA14 KA15

The Vickers hardness number (Hv) is defined as [26] Hv= 1.8544(P/d2) kg/mm2, (1)

where P is the load applied and the Meyers law [26] is

expressed as

P = K1dn (2)

where K1 is the material constant and n is the Meyer index (work hardening coefficient).

The Hv values estimated using equation (1) are shown in Figure 2. The Hv value is found to increase with the increasing load for all the fifteen crystals grown. However, there is no systematic variation observed with the mixed composition/glycine concentration. Figure 3 shows the plots between log P and log d. As these plots are found to be nearly linear, the Meyer index (n) could be evaluated from the slope of the best fitted line. The n values obtained are provided in Table 2. According to Onitsch and Hanneman, n should lie between 1.0 and 1.6 for hard materials and above 1.6 for soft ones [26]. The n values obtained in the present study lie between 1.0 and 1.6 for all the crystals. This indicates that the crystals grown in the present study belong to the hard material category.

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

log p

Fig -3:The log P versus log d plots

Table -2: The estimated work hardening coefficients

Measurement of c along with d leads to the estimation of various mechanical parameters like fracture toughness (Kc), brittleness (B), yield strength (v) and elastic stiffness

80

KA1

100

KA6/p>

constant (C11).The mechanical contact between the indenter

70 KA2

KA3

90 KA7 KA8

80

and the crystal surface produces radial cracks which can be

determined from the crack length (distance between the

H (kg/mm )

H (kg/mm )

H (kg/mm )

H (kg/mm )

KA9

2

2

2

2

60 KA4

KA5

50

40

v

v

30

20

20 30 40 50 60 70 80 90 100 110

Load (x10-3kg)

110

B

100 C

70 KA10

60

50

v

v

40

30

20

20 30 40 50 60 70 80 90 100 110

Load (x10-3kg)

center of indentation mark and crack tip). Fracture toughness (Kc) is the ability of a material containing a crack to resist fracture. It determines how much fracture stress is applied under uniform bending and it is an important parameter for the selection of materials in practical applications where the load exceeds the limit. The variation of crack length and fracture toughness on load can be attributed to the depth of penetration of indenter into

90 D

H (kg/mm2)

H (kg/mm2)

E

80 F

70

surface. The fracture toughness is given by [28]:

32

32

60 Kc = P

v

v

50 c

40

(3)

30

20 30 40 50 60 70 80 90 100 110

Load (x10-3kg)

Here, is the indenter constant (value is 7).

Fig -2: The estimated Hv values

Brittleness (B) determines the fracture without any appreciable deformation. This property helps to understand the laser damage tolerance and it is resolved by the relation [28]:

The elastic stiffness constant is the tightness of bonding between neighboring atoms. It is a property of the material by virtue of which can absorb energy before fracture occurs and it is calculated by the Woosters empirical formula [28]

B = Hv

Kc

(4)

v

v

C11=H 7/4 (6)

The yield strength (v) is the stress at which the material begins to deform plastically and it can be computed from the hardness value using the relation [28]:

= Hv {1 (2 n)} [12.5(2n)]2n (5)

The estimated mechanical parameters are provided in Table

1. It is found that the Kc, v and C11 values increase whereas the B value decreases with the increase in load. This shows the normal mechanical behavior.

   v 2.9

   1(2n)

   Table -3: The estimated mechanical parameters

   Crystal	Kc (kg-3/2) X 104for			B (m-1/2) for			v (MPa) for			C11 (1014 Pa) for
   	25g	50g	100g	25g	50g	100g	25g	50g	100g	25g	50g	100g
   KA1	1.77	3.53	7.07	19.9	12.6	8.90	38.2	48.4	68.2	5.08	7.69	14.1
   KA2	1.32	2.64	5.28	29.2	20.7	12.3	33.9	48.1	56.8	5.97	11.0	14.8
   KA3	4.51	9.01	18.0	6.27	4.06	2.75	50.5	65.3	88.3	3.47	5.44	9.26
   KA4	3.80	7.60	15.2	6.71	4.21	2.78	31.4	39.4	52.1	2.89	4.30	7.02
   KA5	2.90	5.81	11.6	12.9	9.81	6.67	23.6	35.8	48.6	5.71	11.8	20.2
   KA6	1.75	3.49	6.99	23.5	15.7	11.7	46.2	61.4	92.1	6.69	11.0	22.3
   KA7	2.67	5.35	10.7	6.25	3.76	2.78	19.5	24.2	34.7	1.38	1.91	37.8
   KA8	4.09	8.18	16.4	15.2	8.94	5.96	45.3	53.4	71.4	13.7	18.3	30.4
   KA9	1.72	3.44	6.88	27.2	18.9	12.5	60.0	83.2	110	8.37	14.8	24.3
   KA10	1.71	3.41	6.82	29.8	20.2	13.8	52.1	70.5	96.2	9.69	16.5	28.4
   KA11	1.77	3.54	7.09	31.8	24.6	14.1	53.3	82.3	94.9	11.6	24.8	31.8
   KA12	2.04	4.07	8.15	17.8	13.2	8.97	52.5	77.8	105	5.39	10.7	18.3
   KA13	1.69	3.37	6.75	25.2	24.5	15.2	61.0	118.4	146	7.10	22.7	33.0
   KA14	4.28	8.56	17.1	8.69	5.13	3.36	28.4	33.5	43.8	5.60	7.50	11.9
   KA15	0.82	1.65	3.30	44.0	24.2	15.0	22.6	25.0	31.1	5.31	6.35	9.25

2. CONCLUSIONS

Pure and glycine added single crystals (a total of 15) have been grown by the free evaporation of solvent method and characterized thermally and mechanically. Thermal measurements indicate that the crystal with the middle mixed composition [K0.5(NH4)0.5H2PO4 in the solution used for crystallization] exhibits less thermal stability and the decomposition rate with temperature decreases with the increase in ammonium content in the crystal. The microhardness measurements indicate that the pure and glycine added mixed crystals grown in the present study belong to hard materials category. The determined mechanical parameters, viz. Hv, Kc, v, B and C11indicate that all the fifteen crystals grown in the present study exhibit the normal mechanical behavior.

REFERENCES

1. E. Subbarao (1973) Ferroelectrics 5, 267

2. M. Vaezzadeh, B. Wyncke and F. Brehat (1992) J. Phys.

   Condensed Matter 4, 7401

3. M. Rifani, Y.Y. Yin and D.S. Ellion (1995) J. Am. Chem.

   Soc. 117, 1512

4. A. Boukhiris,M. Souhassou, C. Lecomte, B. Wyncke and

   1. Thalal (1998) J. Phys. Condens. Matter 10, 1621

5. K. Srinivasan, P. Ramasamy, A. Cantoni and G. Bocelli (1998) Mater. Sci. Eng. B 52, 129

6. P. Kumaresan, S. MoorthyBabu and P.M. Anbarasan (2001) Optical Mater. 30, 1368

7. Dongli Xu and Dogfeng Xue (2006) J. Alloys Compounds

   449, 353

8. G. Bhagavannarayana, S. Parthiban and S.

   MeenakshiSundaram (2008) Cryst. Growth Des. 8, 446

9. Dongli Xu and Dogfeng Xue (2008) J. Cryst. Growth 310, 1385

10. XiueRen, DongliXu and DongbengXue (2008) J. Cryst.

    Growth 310, 2005

11. P.Rajesh and P. Ramasamy (2009) Mater. Lett. 63, 2260

12. P. Rajesh and P. Ramasamy (2010) Mater. Lett. 64, 798

13. K.D. Parikh, D.J. Deva, B.B. Parekh and M.J. Joshi (2010)

    Cryst. Res. Technol. 45, 603

14. P. Shenoy, K.V. Bangera and G.K. Shivakumar (2010)

    Cryst. Res. Technol. 45, 825

15. P. Rajesh, K. Boopathi and P. Ramasamy (2011) J. Cryst.

    Growth 318, 751

16. P. Sekar Ramasubramanian and C. Mahadevan1991) Cryst.

    Res. Technol. 26, K179

17. T.H. Freeda and C. Mahadevan (2000) Bull. Mater. Sci. 23, 335

18. M. Priya, C.M. Padma, T.H. Freeda and C. Mahadevan (2001) Bull. Mater. Sci. 24,511

19. G. Deepa, T.H. Freeda and C. Mahadevan (2002) Indian J. Phys. 76A, 369

20. A. Anne Assencia and C. Mahadevan (2005) Bull. Mater.

    Sci. 28, 415

21. S. Goma, C.M. Padma and C.K. Mahadevan (2006) Mater.

    Lett. 60, 3701

22. M. Meena and C.K. Mahadevan (2008) Cryst. Res.

    Technol. 43, 166

23. J. Anitha Hudson, C.K. Mahadevan and C.M. Padma (2013) Int. J. Res. Eng. Tech. 2(12), 675.

24. O.V. Mary Sheeja and C.K. Mahadevan (2013) Int. J. Res. Eng. Tech. 2(12), 738.

25. O.V. Mary Sheeja and C.K. Mahadevan (2014) Int. J. Eng. Res. Appl. 4(1:2), 55.

26. J. Anitha Hudson, C.K. Mahadevan and C.M. Padma (2014) Int. J. Eng. Res. Appl. 4(1:2), 257.

27. V. Rajalekshmi and C.K. Mahadevan (2015) Int. J. Inn.

    Res. Sci. Eng. Tech.4(11), 10957

28. Mohd. Shakir, V. Ganesh, M.A. Wahab, G. Bhagavannarayana, K. Kishan Rao (2010) Mater. Sci. Eng. B 172, 9.

BIOGRAPHIES

V. Rajalekshmi, born in Nagercoil, India in 1977 has acquired her academic degrees B.Sc. (Physics,1998), M.Sc. (Physics, 2000), M.Phil. (Physics, 2009) from Manonmanium Sundaranar University. Currently she is a Ph.D Research Scholar of Manonmanium

Sundaranar University. She has about 3 years research experience and her research area is Crystal Growth and Characterization. Also she is serving as an Assistant Professor of Physics at Ponjesly College of Engineering, Nagercoil.

Dr. C.K.Mahadevan, born in Nagercoil, India in 1958 has acquired B.Sc.(1978), M.Sc.(1980), Ph.D.(1984)

and D.Sc.(2002) degrees in Physics from reputed Institutions in India. After serving for some time in different places in India and USA, he had his (major) service in S.T.Hindu College,

Nagercoil for more than 26 years. Currently, he is a Professor of Physics at PSN College of Engineering and Technology, Tirunelveli. He has about 29 years teaching experience (taught B.Sc., M.Sc., M.Phil and Ph.D. Students) and 34 years research experience (Guided 2 Research Associates and more than 40 Ph.D. Scholars, availed 10 Externally Funded Projects, organized 11 Regional/National Seminars/Conferences, published 1 Review Article and 206 Research Papers in International Journals, published 138 Articles in Proceedings, and presented 570 Papers and 68 Invited/Keynote Talks/Addresses in Conferences). His major research area is Solid State Materials [Preparation and characterization of new and hybrid (doped/mixed) crystalline and nano structured materials to explore potential applications]. He is a winner of several coveted awards and honors for his teaching, research and related activities.