4. LATTICE VARIATION

X-ray diffraction data collection on powdered samples of all the

crystals grown along with the determination of lattice parameters are dealt

with in this chapter. The results are also reported and discussed.

4.1. X-ray Diffraction Measurements

X-ray diffraction is a tool for the investigation of the fine structure

of matter. To have a thorough understanding of a material, information

about the purity, crystallinity, crystal structure and crystal perfection is

required. The mechanical, chemical or electrical properties of the material

strongly depends on its internal structure. A large variety of techniques

employing different tools and equipments have been developed for this

purpose.

The major technique employed for the crystallographic characterization

of crystals which involves the determination of the lattice parameters and

the contents of the unit cell is the X-ray diffiaction method. X-ray

diffraction data gives the angle of scattering (20) and the corresponding

intensities of diffracted beam for each reflection.

As the present investigation is on mixed crystals, structural

characterization is one of the important characterizations to be done. For

this purpose, X-ray diffraction data were collected from the powdered

samples of all the twenty six grown crystals using an automated X-ray

diffractometer (available at Central Electrochemical Research Institute,

Karaikudi, Tamilnadu) with monochramated CUK a radiation at a temperature

of 25±1°C. The data collection parameters are given in table 14.

Table 14: X-ray powder diffraction data collection parameters

Instrument description Automated X-ray diffractometer

60

Specimen form

Temperature

Radiation type

?, Value used

Detector used

29 range

Scan speed

Filteratjon method

Loaded powder

25± 1°C

CUKa

1.5418A

Scintillation counter

20 to 90°

O.02°/s

Monochromator

Background correction and Smoothnormalization method followed

4.2. Indexing the Data

Indexing the X-ray powder diffraction pattern consists of assigning

the three Miller indices h, k, I to each reflection. The procedures of

Lipson and Steeple [116] were used for this purpose.

NaCl, KCI and KBr belong to face centered cubic structure.

Hence the following relation for cubic system was used for indexing the

data.

sin 2O= 2

(h 2 +k 2 + 12)

4a

where O kh, is the Bragg angle, X the wavelength of radiation used, a

the lattice parameter and h, k, I the Miller indices. The above equation

can be rewritten as

sin 2O1

h2 +k2 + 12 4a2

Since (h2 +k 2 + 12) is always an integral and X 2 /4a2 is a constant

for any one pattern, the problem of indexing the pattern of a cubic

substance is one of finding a set of integers (h 2 + k2 + 12) that will yield

a constant quotient when divided one by one into the observed sin 20

values. Once the proper set of (h 2 + k2 + 12) is found out then the

Miller indices (h, k, I) and the lattice parameter 'a' can be found out

[1171. This method was used to index the twentythree mixed (binary and

ternary) crystals since the unit cell was unknown.

In the case of end member crystals, since the lattice parameter is

known, the procedure is to calculate X2 /4a2 and divide this value into

the observed sin 20 values to obtain the value of (h 2 + k2 + 12) for each

time from which h, k, I can be found out. This procedure was used to

index the X-ray diffraction patterns obtained for NaCl, KC1 and KBr.

62

Indexed X-ray powder diffraction data along with the calculated

lattice parameters for each reflection for all the twenty six crystals

are provided in tables 15-40.

4.3. Lattice Parameters

The accurate determination of the lattice parameters of crystalline

materials is of great importance, owing to its application in many aspects

of solid state physics.

Lattice parameter, being a basic crystallographic parameter, is a

measure of the unit cell and indirectly of the interatomic distance. Also,

it provides information about the phase of the crystal and its purity. In

developing the phase-equilibrium diagrams, the data on lattice parameters

are found to be necessary [118]. Lattice parameters are also required for

the calculation of physical properties such as compressibility, lattice

energy, refractive index, etc. A comparison of the values of the densities

determined by X-ray method (for which lattice parameters are necessary)

with those obtained by the macroscopic method provides knowledge of

the defects inside the crystal [119]. Lattice parameter data determined at

different temperatures is useful for the calculation of thermal expansion of

crystals. In the case of mixed crystals, determination of precise values of

lattice spacings in solid solutions has contributed to the understanding of a

number of factors which influence the stability and properties [10].

Since the present investigation is on mixed crystals, determination

of lattice parameters and its dependence with composition is an important

factor. Calculated lattice parameters along with estimated standard

deviations are provided in table 41.

Table 15: Indexed X-ray diffraction data for NaCI

63

S1.No. 20 (0)

1. 27.3

2. 31.6

3. 45.4

4. 53.7

5. 56.3

6. 66.1

d (A)

3.262

2.827

1.995

1.706

1.633

1.412

hkl a(A)

111 5.6498

200 5.6545

220 5.6421

3 11 5.6582

222 5.6581

400 5.6493

I

lIIo

79

9

894

100

214

24

27

3

73

8

33

4

Table 16: Indexed X-ray diffraction data for KCI

S1.No

200

d(A)

I

"0 hkl a(A)

1. 28.3

3.153

125

61

200 6.3051

2. 40.4

2.231

203

100

220 6.3106

3. 50.0

1.823

30

15

222 6.3163

4. 58.4

1.580

20

10

4 00 6.3200

5. 66.1

1.413

23

11

420 6.3182

64

Table 17: Indexed X-ray diffraction data for KBr

SI.No. 20(°) d (A) I I/Ia hkl a(A)

1.

2.

3.

4.

5.

6.

7.

8.

9.

23.4

27.0

38.5

45.5

47.6

55.5

61.3

62.8

69.6

3.804

3.295

2.335

1.992

1.910

1.655

1.512

1.479

1.350

111

200

220

311

222

400

331

420

422

6.5890

6.5908

6.6056

6.6051

6.6153

6.6185

6.59 16

6.6145

6.6135

120

21

515

91

564

100

46

8

82

15

27

5

16

3

87

15

44

8

Table 18: Indexed X-ray diffraction data for (NaC1)05(KC1)05

S1.No. 20(°) d (A) I III h k I

1. 27.4 3.252 71 20 1112. 31.9 2.803 219 60 2003. 45.7 1.984 140 38 2204. 56.7 1.622 57 10 2225. 75.6 1.257 51 14 4206. 84.2 1.149 32 9 4227. 28.6 3.119 364 100 2008. 40.7 2.215 244 67 2209. 50.4 1.809 84 23 222

10. 58.9 1.567 41 11 400

11. 66.6 1.403 94 26 42012. 74.0 1.280 55 15 422

13. 88.0 1.109 25 7 440

a(A)

5.6378

5.6107

5.6150

5.6238

5.6249

5.6332

6.2700

6.2700

6.2720

6.2718

6.2795

6.2754

6.2771

Table 19: Indexed X-ray diffraction data for (NaC1)0.5(KB)0.5

SI.No. 20() d (A) I

65

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

32

24

13

12

20

100

62

22

17

26

18

32.2

45.9

75.6

84.1

24.0

27.6

39.3

48.5

56.6

63.8

70.7

2.778

1.975

1.257

1.150

3.705

3.229

2.291

1.875

1.625

1.458

1.331

213

155

84

82

134

658

408

148

115

174

117

200

220

420

422

ill

200

220

222

400

420

422

5.5597

5.5919

5.6249

5.6386

6.4221

6.4637

6.4841

6.5020

6.5043

6.5241

6.5275

Table Indexed X-ray diffraction data for (KC1)0.5(KBF)o.5

S1.No. 20(°) d(A)

1.

2.

3.

4.

5.

6.

7.

8.

9.

24.1

27.9

39.8

47.1

49.3

57.5

65.0

72.1

85.5

3.690

3.195

2.263

1.928

1.847

1.601

1.434

1.309

1.135

Ill

200

220

311

222

400

420

422

440

a(A)

6.3959

6.3955

6.4059

6.3992

6.4029

6.4110

6.4165

6.4175

6.4244

84

11

752

100

410

55

71

9

112

15

252

34

164

22

91

12

63

8

Table 21: Indexed X-ray diffraction data for (NaC1)o.i(KC1)0.7(1<)0.2

S1.No.

1.

2.

3.

4.

5.

6.

20()

28.0

40.0

49.6

57.9

65.5

72.7

d(A)

3.181

2.250

1.838

1.592

1.424

1.299

hkl

200

220

222

400

420

422

a(A)

6.3626

6.3639

6.3670

6.3674

6.3696

6.3651

I

423

100

250

59

59

14

54

13

39

9

58

14

Table 22: Indexed X-ray diffraction data for (NaC1)0.2(KCI)0.6(KBr)o.2

S1.No.

1.

2.

3.

4.

5.

6.

7.

8.

9.

28)

31.7

45.3

75.0

28.0

40.0

49.4

57.7

65.4

72.5

d (A)

2.822

2.001

1.266

3.183

2.253

1.843

1.596

1.425

1.303

hkl

200

220

420

200

220

222

400

420

422

a(A)

5.6440

5.6595

5.6606

6.3666

6.3734

6.3827

6.3825

6.3739

6.3833

I

1/10

51

15

45

14

18

6

330

100

242

73

61

18

52

16

86

26

57

17

Table 23: Indexed X-ray diffraction data for (NaCI)0.3(KCI)05(KBr)02

S1.No. 20(°) d (A) I I/Is h k a (A)

67

2.826

'.999

1.635

3.185

2.253

1.841

1.592

1.426

1.299

200

220

222

200

220

222

400

420

422

5.65 10

5.6541

5.6650

6.3699

6.3718

6.3784

6.3679

6.3784

6.3623

1. 31.6

2. 45.3

3. 56.2

4. 28.0

5. 40.0

6. 49.5

7. 57.9

8. 65.4

9. 72.8

85

11

33

4

24

3

789

100

305

31

51

7

19

2

52

7

65

8

Table 24: Indexed X-ray diffraction data for (NaCI)04(KC!)04(KBr)02

SI.No 20(°)

d(A)

I

1/10 hkl a(A)

2.825

1.999

1.634

1.265

3.188

2.255

1.842

1.598

1.429

1.304

200

220

222

420

200

220

222

400

420

422

5.6495

5.6549

5.6607

5.6580

6.3757

6.3773

6.3817

6.3921

6.3896

6.3860

1. 31.7

2. 45.3

3. 56.2

4. 75.0

5. 28.0

6. 40.0

7. 49.4

8. 57.6

9. 65.3

10. 72.4

79

32

45

18

17

7

12

5

245

100

115

47

27

11

24

10

28

12

16

7

Table 25: Indexed X-ray diffraction data for (NaCI)o.5(KCI)03(KBr)02 68

S1.No. 28(e) d (A) I I/La h k 1 a (A)

1. 31.6 2.826 155 40 200 5.6513

2. 45.3 1.998 103 27 220 5.6521

3. 56.2 1.635 31 8 222 5.6644

4. 65.9 1.416 22 6 400 5.6660

5. 75.0 1.266 28 7 420 5.6597

6. 24.1 3.693 29 7 111 6.39667. 27.9 3.198 385 100 200 6.3959

8. 39.8 2.265 224 58 220 6.4055

9. 49.3 1.848 71 19 222 6.403010. 57.4 1.603 27 7 400 6.412711. 65.1 1.431 39 10 420 6.401012. 72.1 1.310 50 13 422 6.4161

Table 26: Indexed X-ray diffraction data for (NaC1)oo(KC1)o(KBr)02

S1.No. 20(°) d (A) I I/La h k I a (A)

1. 31.9 2.803 428 74 200 5.63622. 45.7 1.984 249 43 220 5.63063. 56.7 1.622 99 17 222 5.623 7

4. 66.4 1.407 71 12 400 5.63155. 75.5 1.258 88 15 420 5.6312

6. 84.2 1.149 75 13 422 5.6331

7. 27.9 3.195 575 100 200 6.3955

8. 39.8 2.263 358 62 220 6.4058

9. 49.2 1.850 139 24 222 6.4150

10. 64.9 1.436 129 22 420 6.4252

11. 72.0 1.310 101 18 422 6.4251

Table 27: Indexed X-ray diffraction data for (NaC1)0.7(KC1)0.1(KBr)02

69

IS1.No

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

20(°)

32.2

46.0

66.7

75.7

84.4

24.1

27.9

39.7

49.0

57.0

64.4

71.4

d(A)

2.778

1.971

1.401

1.255

1.147

3.690

3.195

2.268

1.857

1.614

1.446

1.320

hkl

200

220

400

420

422

111

200

220

222

400

420

422

a(A)

5.5597

5.5803

5.6091

5.6180

5.6223

6.3958

6.3955

6.4213

6.4396

6.4624

6.4697

6.4719

346

95

228

63

54

15

85

23

77

21

75

21

364

100

197

54

86

24

114

31

88

24

68

19

Table 28: Indexed X-ray diffraction data for (NaC1)o.1(KCI)05(KBr)04

S1.No

20()

d (A)

I

hkl a(A)

1. 28.2

3.162

1017

100

200

6.3288

2. 40.1

2.247

477

47

220

6.3599

3. 49.6

1.836

135

13

222

6.3665

4. 57.8

1.594

136

13

400

6.3805

5. 65.3

1.428

202

20

420

6.3902

6. 72.4

1.304

78

8

422

6.3944

I

14299576385

633406

6115094

160109

1/10

22169

1013

100641024152517

SI.No.

1.2.3.4.5.6.7.8.9.10.H.12.

20(°)

32.145.775.485.424.127.939.847.149.257.464.972.0

d (A)

2.7861.9841.2601.1363.6903.1952.2631.9281.8501.6041.4361.310

a(A)

5.57665.61505.63765.56866.39596.39556.40596.39926.41516.42126.42536.4252

hkl

200220420422111200220311222400420422

Table 29: Indexed X-ray diffraction data for (NaCI)0.2(KCI)04(KBr)04

70

SI.No.

1.2.3.4.5.6.7.8.9.10.11.12.13.

2e(°)

27.632.045.854.256.875.684.428.740.950.558.966.674.1

d(A)

3.2292.7951.9801.6911.6201.2571.1473.1082.2051.8061.5671.4031.278

hkl

111200220311222420422200220222400420422

a(A)

5.59775.59365.60345.61255.6 1475.62495.62236.22086.24076.26046.27186.27956.2681

I

II1()

86

11

765

100

329

43

28

4

124

16

115

1570

9

230

30

128

17

43

6

26

3

96

13

32

4

Table 30: Indexed X-ray diffraction data for (NaC1)03(KCI)03(KBr)04

Table 31: Indexed X-ray diffraction data for (NaCI)0.4(KCI)02(KBr)04

71

S1.No.

1.2.3.4.

5.

6.7.

8.9.10.11.12.13.

20(°)

31.945.6

66.475.4

84.824.127.739.646.949.057.1

64.671.7

d (A)

2.8031.9881.4071.2601.1423.6903.2182.2741.9361.8571.6121.4421.315

hki

2002204 00420422111200220311222400420422

a(A)

5.6 1075.62675.63155.63765.6008

6.39596.44086.43696.42496.43966.45216.45186.4484

11'IO

201

28

135

19

65

9

69

9

62

9

109

15

727

100

469

65

73

10

183

25

109

15

170

23

126

17

Table 32: Indexed X-ray diffraction data for (NaCI)05(KCI)01(KBr)04

Si. No. 28(°)

d (A)

I

111<) hkl

a(A)

2.7951.9801.2571.1483.7053.2182.2851.8681.6201.4501.323

200220420422111200220222400420422

5.59365.60345.62495.62776.42216.44086.46836.47686.48326.48776.4877

32.02. 45.83. 75.6

4. 84.35. 24.06. 27.77. 39.48. 48.79. 56.810

64.211

71.2

256

46158

2984

1588

16113

21551

100383

70145

26124

23162

29121

22

Table 33: Indexed X-ray diffraction data for (NaCI)o.i(KCI)04(KBr)05

S1.No. 20(°) d (A) I I/Ic, h k 1 a (A)

72

3.660

3.184

2.258

1.843

1.599

1.434

1.310

1.136

111

200

220

222

4 00

420

422

440

6.3440

6.3731

6.3905

6.3907

6.4008

6.4165

6.4252

6.4304

1. 24.3

2. 28.0

3. 39.9

4. 49.4

5. 57.6

6. 65.0

7. 72.0

8. 85.4

80

10

785

100

332

42

150

19

80

10

130

17

101

13

58

7

Table 34: Indexed X-ray diffraction data for (NaCI)02(KC1)03(KBr)05

S1.No. OR

d (A)

I

hkl a(A)

2.795

1.980

3.690

3.195

2.268

1.936

1.854

1.607

1.440

1.314

200

220

111

200

220

311

222

400

420

422

5.5936

5.6034

6.3959

6.3955

6.4214

6.4249

6.4273

6.4314

6.4429

6.4407

L

32.0

2. 45.8

3. 24.1

4. 27.9

5. 39.7

6. 46.9

7. 49.1

8. 57.3

9. 64.7

10

71.8

89

9

70

7

98

10

949

100

339

36

71

7

171

18

113

12

162

17

122

13

I

104

81

65

105

606

392

71

176

95

151

109

1110

17

13

11

17

100

65

12

29

16

25

18

Table 35: Indexed X-ray diffraction data for (NaCI)0.3(KCI)0.2(KBr)0.5

73

S1.No

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

II.

20()

32.0

45.7

84.7

24.1

27.8

39.5

46.7

48.9

57.0

64.5

71.5

d(A)

2.795

1.984

1.143

3.690

3.206

2.279

1.943

1.861

1.614

1.444

1.318

hkl

200

220

422

111

200

220

311

222

4 00

420

422

a(A)

5.5936

5.6150

5.6061

6.3959

6.4181

6.4526

6.4509

6.4508

6.4624

6.4608

6.4641

Table 36: Indexed X-ray diffraction data (NaCI)0.4(KC1)o.1(KBr)0.5

S1.No. 20(°) d (A) I I/1 h k I a(A)

1. 32.1 2.786 151 22 200

5.5766

2. 45.8 1.980 101 15 220

5.6034

3. 75.5 1.258 67 10 420

5.6313

4. 84.4 1.147 88 13 422

5.6223

5. 24.0 3.705 125 18 111

6.4221

6. 27.7 3.218 688 100 200

6.4407

7. 39.5 2.279 423 61 220

6.4525

8. 46.6 1.947 80 12 3 11

6.4531

9. 48.8 1.865 192 28 222

6.4644

10. 56.9 1.617 113 16 400

6.4728

11. 64.3 1.448 167 24 420

6.4787

12. 71.2 1.323 121 18 422

6.4876

Table 37: Indexed X-ray diffraction data for (NaCI)o.i(KC1)0.3(KBr)0.6

SI.No. 20(°) d (A) I I/L,, h k 1 a (A)

74

1. 24.1

3.690

102

19

111

6.3969

2. 27.8

3.206

544

100

200

6.4181

3. 39.6

2.274

403

74

220

6.4369

4. 49.0

1.857

137

25

222

6.4396

5. 57.1

1.612

101

19

400

6.452 1

6. 64.6

1.442

164

30

420

6.45 19

7. 71.5

1.318

110

20

422

6.4641

8. 84.8

1.142

69

13

440

6.4672

Table 38: Indexed X-ray diffraction data for (NaCI)oj(KCI)02(KBr)06

SLNo

20(°)

d (A)

I

1110 hkl a(A)

2.795

1.955

3.705

3.218

2.285

1.865

1.620

1.448

1.323

1.147

200

220

111

200

220

222

400

420

422

440

5.5936

5.5349

6.4221

6.4408

6.4683

6.4644

6.4833

6.4787

6.4876

6.4921

1. 32.0

2. 46.4

3. 24.0

4. 27.7

5. 39.4

6. 48.8

7. 56.8

8. 64.3

9. 71.2

10. 84.4

89

13

79

11

113

16

692

100

435

63

192

28

98

11

172

25

134

19

73

11

Table 39: Indexed X-ray diffraction data for (NaC1)0.3(KCI)o.1(KBr)0,6

S1.No. 20(°) d (A) I 1/10 h k 1 a (A)

75

2.795

1.971

1.255

3.720

3.229

2.291

1.872

1.622

1.452

1.326

1.149

200

220

420

111

200

220

222

4 00

420

422

440

5.5936

5.5804

5.6186

6.4486

6.4637

6.4841

6.4894

6.4938

6.4968

6.5035

6.5046

1. 32.0

2. 46.0

3. 75.7

4. 23.9

5. 27.6

6. 39.3

7. 48.6

8. 56.7

9. 64.1

10. 71.0

11. 84.2

138

18

93

12

74

10

153

20

772

100

544

70

209

27

146

19

198

26

146

19

92

12

Table 40: Indexed X-ray diffraction data for (NaC1)o1(KC1)o.1(KBr)03

SI.No. 20(°)

d(A)

I

1/10 hkl

a(A)

1. 23.8

3.736

146

16

111

6.4753

2. 27.5

3.241

932

100

200

6.4867

3. 39.2

2.296

554

59

220

6.4999

4. 48.4

1.879

168

18

222

6.5 146

5. 56.5

1.627

108

12

400

6.5 148

6. 63.8

1.458

222

24

420

6.5241

7. 70.7

1.331

121

13

422

6.5275

8. 83.8

1.153

87

9

440

6.5299

76

Table 41: Lattice constants. e.s.d.'s are given in paranthesis. Also, theliterature values for the end members are given in paranthesis.

Sample System with Lattice constants ( A)No. initial composition As perFor mixed Total

For NaCl phasephase

average Retger' Srule

NaCl

KCI

KBr

NaCI0 5KC105

NaC10 sKBro

KCI0 5K13ro5

NaCI0 1 KCIO 7KBr02

NaC10 7KC10 6KBr02

NaCl0 3 KC10 5KBr02

NaCI04KCI04KI3r02

NaC105 KCI0 3KBr02

NaCI06KC102KBr02

NaCL07 KCI0 1KBr02

NaCl(). 1 KC10 5KBr04

NaCIO2KCI04KBr04

NaC103 KCI0 3KBr04

NaC10 4 KC10 2K131`04

NaCI0 5 KC10 1KBr04

NaC10 1KC104KBr05

NaC10 KC10 3KBr05

NaCl0 3 KC10 2KBrO5

NaCI04 KC10 1KBr05

NaC10 1 KC10 3KB1706

NaCI0 2 KCI0 2KBr06

NaCI0 3 KC10 1KBr06

NaCI0 1 KC10 1K13r08

5.6498(68)(5 .64 0)

6.31 63(35)(6.293)

6.6048(1 8)(6.600)

5.6231(91)

5.5921(166)

5.6547(75)

5.6567(59)

5.6558(41)

5.6587(60)

5.63 10(4 1)

5.6167(50)

5.6098(111)

5.6263(103)

5.62 15(126)

5.6177(95)

5.5985(49)

5.6043(99)

5.6084(109)

5.5642(233)

5.6064(150)

6.2746(31) 6.0000

6.5144(94) 6.2467

6.4119(57) 6.4119

6.3672(15) 6.3672

6.3806(38) 6.1357

6.3715(57) 6.1331

6.3874(39) 6.0925

6.4082(63) 6.0936

6.4218(47) 5.9866

6.4609(12) 6.0871

6.3829(97) 6.3829

6.2679(45) 5.9331

6.4217(41) 6.1165

6.4480(50) 6.1895

6.4839(44) 6.2324

6.4082(103) 6.4082

6.4356(64) 6.2390

6.4598(46) 6.2787

6.4759(84) 6.2292

6.4519(86) 6.4519

6.4785(87) 6.2863

6.4959(57) 6.2757

6.5202(56) 6.5202

6.1297

5.9787

6.4588

6.3243

6.2764

6.2004

6.1336

6.0799

5.9999

5.9343

6.3919

6.3343

6.2646

6.2256

6.1455

6.3834

6.3244

6.3099

6.2412

6.4243

6.3510

6.3392

6.4913

2

3

4

5

6

7

8

I,]

1 0

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

77

4.4. Results and Discussion

Lattice parameters of the end member crystals obtained in the

present study compare well with those reported in the literature. However,

to compare the lattice parameters of the ternary mixed crystals, no reported

values are available.

Analysis of the X-ray diffraction peaks shows that, for crystals

with x = 0.1, all the peaks can be indexed with a single fcc lattice and

the lattice parameter obtained almost obeys Retger's rule [14] extended to

ternary mixed crystals:

a 3= xa1 + (y - x) a23 + ( 1 - y) a33

where a is the lattice parameter of the mixed crystal and a 1 , a2 and a3

are respectively the lattice parameters of NaCl, KCI and KBr crystals.

However, for crystals with x>0.1, it has been found that all the X-ray

diffraction peaks can be indexed with two fcc phases instead of one which

shows the existence of two fcc phases. The calculated lattice parameters

show that one phase nearly corresponds to pure NaCl and the other phase

corresponds to the mixed system. A similar result was reported for the

KBr - K! mixed crystals [28].

Since no KCI or KBr lines are found to be separated out in the

diffraction pattern, the mixed phase should contain all the KCI and KBr

present in the crystal. Lattice parameters calculated by assuming the mixed

phase to contain only KCI and KBr (as NaCl forms a separate lattice) in

the appropriate molecular ratio and applying Retger's rule was found to be

greater than the observed lattice parameter. This decrease in the observed

lattice parameter showed that the mixed phase contained some NaCl also

78

in addition to KCI and KBr. This NaCl content was estimated by finding

the deviation between the observed and calculated (using Retger's rule and

assuming the mixed phase to contain only KC1 and KBr) lattice volumes.

This composition in the mixed phase is given in table 42.

Separation of NaCl phase from the mixed lattice may be due to the

large percentage deviation in lattice parameters between NaCl and KCI

(11.796%) and NaCl and KBr (17.091%). This is shown in the equimolar

binary mixed crystals also. For KCI and KBr, the percentage deviation in

lattice parameters is only 4.735% and this system can form a continuous

series of solid solutions. Hence, for higher concentrations of NaCl, NaCl

is forming a separate lattice and KCI - KBr with some NaCl is fonning

another lattice.

Table 42: Composition of the mixed phase

79

System (with initial Compositioncomposition) NaCI KC1 KBr

(NaCI)02(KCI)06(K Br)02

(NaCI)03(KC1)05(KBr)02

(NaC1)04(KC1)04(KBr)0

(NaC1)(KC1)03(KBr)02

(NaCI)06(KC1)02(KBr)02

(NaC 1) 7(KCI)01 (KBr)0

(NaC I)o2(KC1)04(KBr)04

(NaCI)03(KCI)03(KBr)04

(NaC l)o4(KCJ)02(KBr)04

(NaCI)05(KCI)0 i(KBr)04

(NaCI)0(KCI)03(KBr)05

(NaC l)o.3(KCI)o.2(KBr)05

(NaCI)04(KCI)oi(KBr)05

(NaCI)02(KCI)o2(KBr)06

(N aCt)o 3(KCI)0 i(KBr)06

0.001

0.003

0.003

0.003

0.004

0.008

0.028

0.009

0.009

0.014

0.010

0.008

0.014

0.010

0.010

0.761

0.727

0.682

0.610

0.537

0.304

0.523

0.405

0.329

0.077

0.3 53

0.311

0.121

0.206

0.140

0.238

0.270

0.315

0.387

0.459

0.688

0.449

0.586

0.662

0.909

0.637

0.681

0.865

0.784

0.850