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98 Chapter 5

5.1. INTRODUCTION

The characterization of the crystals is an important tool of the

study of crystals. This helps the crystal grower to assess the quality,

nature and property of the crystals. A large number of experimental

techniques exist to assess the structure, bonding, composition, quality

and the presence of its constituent elements. The experimental methods

include spectroscopic analysis, thermo gravimetric analysis, DSC,

elemental analysis etc. A brief description of the principles involved in

the measurement and salient features of the instruments and

characterization of rare earth mixed oxalate crystals in each case is

given in this chapter.

5.2. X-ray Analysis

X-Ray Powder Diffractometry is the most powerful technique for

structural analysis, capable of providing information about structure of a

material at the atomic level. In this particular case the powder diffraction

method had been employed for the study. Figures 5.1, 5.2, 5.3, 5.4, 5.5, 5.6,

5.7 and 5.8 show the X-ray powder diffractogram of Y2(C2O4)3.14H2O,

Y2Ba(C2O4)4.8H2O,Y2BaCu(C2O4)5.8H2O, Pr2BaCu(C2O4)5.9H2O,

Nd2BaCu(C2O4)5.12H2O, Gd2BaCu(C2O4)5. 13H2O and Dy2BaCu(C2O4)5.12H2O

crystals respectively. The number of water of crystallization of the

Spectroscopic and Thermal Characterization 99

crystals is varied from eight to fourteen in conformation with the results

of thermal analysis.

Hansson1 made a detailed study of the crystals and molecular

structure of Neodymium Oxalate 10.5 Hydrate. Results were similar to

those of decahydrates2. Here also it is seen that whether the water of

crystallisation is varied, it will not affect the crystal structure. The

varying water content observed for these crystals might be explained by

an inclusion of different amounts of water in the cavities depending on

the conditions of crystal growth or slight changes in the growth

environment.

The Bruker D8 Advance X-ray Diffractometer was used to take

the diffraction patterns of the crystals with CuKα radiation of

wavelength λ= 1.5418Å. The samples were scanned over the required

range for 2θ (00 - 800) at a scan speed of 300/s. The analysis of the

spectra confirmed the crystalline nature of the samples. X-ray diffraction

parameters of YOx, YBaOx, YBaCuOx, PrBaCuOx, NdBaCuOx,

GdBaCuOx & DyBaCuOx are given in the table 5.1, the unit cell data of

the crystals are given in the tables 5.2 -5.8 and X-ray diffraction patterns

of the crystals are given in the figures 5.1 –5.7 respectively. It may be

100 Chapter 5

noted that ’d’ values depend on the atomic dimension of the constituent

atoms. It is found that these crystals are of tetragonal system.

Table 5.1 The cell parameters of YOx, YBaOx, YBaCuOx, PrBaCuOx, Nd BaCuOx, GdBaCuOx, & DyBaCuOx.

Crystals a =b(Å) c(Å) α=β=γ (degrees) Volume(Å)3

YOx 10.67 11 90 1252.3379

YBaOx 10.1 12.9 90 1315.929

YBaCuOx 9.748 14.2 90 1349.3376

PrBaCuOx 10.04 14.76 90 1487.8316

Nd BaCuOx 9.92 16 90 1574.5024

GdBaCuOx 9.75 15 90 1425.9375

DyBaCuOx 9.76 14.8 90 1409.8125


Fig. 5.1 X-ray Powder diffractogram of Y2 (C2O4)3. 14H2O

Table 5.2 X-ray powder diffraction data for Y2 (C2O4)3.14H2O crystals

Sl.No 2θ0 d(obs.) d(cal.) hkl I/Imax

1 13.822 6.4 0164 6.2219 2 111 10.2564

2 18.573 4.77349 4.77177 210 100

3 25.919 3.43485 3.46763 103 10.2564

4 31.076 2.87554 2.87606 312 7.69230

5 32.222 2.77583 2.75000 004 20.513

6 34.818 2.57462 2.58372 114 12.8205

7 38.977 2.30894 2.30286 323 10.2564

8 39.767 2.26486 2.28717 332 12.8205

9 47.605 1.90864 1.90444 225 14.1026

10 61.269 1.51170 1.51622 515 12.8205

11 64.772 1.43815 1.43196 445 15.6

102 Chapter 5

Fig. 5.2 X-ray Powder diffractogram of Y2Ba (C2O4)4.8H2O crystals

Table 5.3 X-ray powder diffraction data for Y2Ba (C2O4)4.8H2O crystals

Sl.No 2θ(0) d (obs.) d (cal) h k l I/Imax

1 11.178 7.90922 7.9525 1 0 1 10.4167

2 12.456 7.10065 7.14178 110 100

3 18.705 4.73995 4.70251 2 0 1 14.5863

4 24.788 3.58888 3.57089 220 25

5 37.392 2.40309 2.40660 4 11 8.3


Fig.5.3 X-ray Powder diffractogram of Y2BaCu (C2O4)4.8 H2O crystals

Table 5.4 X-ray powder diffraction data for Y2BaCu(C2O4)5.8H2O crystals

Sl.No 2θ(0) d(obs.) d(cal.) h k l I/Imax

1 9.065 9.74763 9.7487 100 100

2 12.425 7.11801 7.1000 002 54.76

3 13.908 6.36214 6.20129 111 26.19048

4 17.984 4.92837 4.94579 112 19.04762

4 18.67 4.74900 4.7333 003 52.38095

5 24.767 3.59197 3.5500 004 47.6190

6 37.368 2.40457 2.40205 401 11.9048

7 44.402 2.03859 2.0671 333 11.9048

8 45.567 1.98915 1.97999 423 9.52381

9 47.383 1.91708 1.91188 5 10 14.2857

10 48.401 1.87911 1.85762 424 9.52381

104 Chapter 5

Fig. 5.4 X-ray Powder diffractogram of Pr2BaCu (C2O4)5. 9H2O crystals

Table 5.5 X-ray powder diffraction data for Pr2BaCu (C2O4)5 .9H2O crystals

Sl.No. d (observe) d (cal). 2θ(0) h k l I /Imax

1. 10.02019 10.040 8.818 100 24.359

2. 6.5541 6.3978 13.499 111 42.3077

3. 5.095024 5.0200 17.391 200 19.2308

4. 4.77756 4.75264 18.557 201 100

5. 4.23318 4.29566 20.967 211 15.3846

6 3.69976 3.69000 24.034 004 12.8205

7. 3.50820 3.51379 25.368 203 26.9231

8. 3.04433 3.04792 29.313 302 16.6667

9 2.77938 2.78460 32.180 320 15.3846

10. 2.60799 2.60531 34.358 322 16.6667

11. 2.32223 2.32441 38.358 116 24.359

12.. 2.18111 2.18239 41.363 305 12.8205

13 2.04045 2.04243 44.36 423 20.5128

14.. 1.95623 1.95172 46.378 511 19.2308


Fig. 5.5 X-ray Powder diffractogram of Nd2BaCu (C2O4)5 12 H2O crystals

Table 5.6 X-ray powder diffraction data for Nd2BaCu (C2O4)5.12H2O crystals

Sl.No 2θ 0 d(obs.)Å d(cal.)Å hkl I/Imax

1. 8.905 9.92284 9.92000 100 15.490

2. 13.680 6.46771 6.42425 111 23.944

3. 18.617 4.76227 4.7376 201 100

4. 25.583 3.4792 3.47474 114 19.7183

5. 30.361 2.94167 2.9304 223 11.2676

6. 33.127 2.70207 2.70393 313 14.0845

7. 48.225 1.88556 1.8879 335 25.3521

8. 68.920 1.36136 1.36262 720 24.6479

106 Chapter 5

Fig.5.6 X-ray Powder diffractogram of Gd2BaCu(C2O4)5.13 H2O crystals

Table 5.7 X-ray powder diffraction data for Gd2BaCu (C2O4)5.13 H2O crystals

Sl.No 2θ 0 d (obs.)Å d (cal.)Å hkl I/Imax

1. 9.052 9.76153 9.7500 100 34.6154

2. 12.973 6.8186 6.89429 110 23.0769

3. 13.860 6.38402 6.26430 111 30.7692

4. 17.886 4.9551 4.87500 200 23.0769

5. 18.690 4.74390 4.63629 201 100

6. 29.454 3.03017 3.02008 311 43.5897

7. 34.805 2.57556 2.54386 322 26.9230

8. 38.987 2.30835 2.31815 402 32.0513

9. 45.156 2.0063 2.0086 325 29.4872


Fig.5.7 X-ray Powder diffractogram of Dy2BaCu (C2O4)5. 12 H2O crystals

Table 5.8 X-ray powder diffraction data for Dy2BaCu(C2O4)5. 12 H2O crystals

Sl.No 2θ 0 d(obs.)Å d(cal.)Å hkl I/Imax

1. 9.052 9.76192 9.7600 1 0 0 100

2. 13.740 6.43974 6.25476 11 1 29.78

3. 18.615 4.76283 4.63456 2 0 1 68.085

4. 26.908 3.31079 3.36055 2 2 1 29.78

5. 32.713 2.73531 2.71594 3 0 3 36.73

6. 38.930 2.31162 2.31728 4 0 2 29.78

108 Chapter 5

5.3 Analysis Infrared

The infrared absorption studies are an important tool in the

investigation of the molecular structure of crystals. Infra red radiation

promotes transitions in a molecule between rotational and vibrational energy

levels of the ground electronic energy states. It gives information about certain

group of atoms or functional groups present in the material. It was observed in

the present investigation that all the grown crystals showed almost identical

vibrationl modes and some have slight shift, which can be attributed to the

presence of constituent Rare Earth, Barium and Copper elements.

The FT-IR spectra of the crystalline samples of grown crystals were

recorded using KBr pellet method by Thermo-Nicolet Avator 370 in the

spectral range of 400cm-1 _ 4000cm-1.

5. 3 (a) IR spectrum of Yttrium Oxalate crystal

Fig.5.8. IR absorption spectrum of YOx crystals


The IR absorption spectrum of (YOx) crystal is shown in Fig.5.8.

The stretching vibration of water molecules is expected in the region 3000-

3600 cm-1. The broad and sharp band at 3357cm-1 established the presence of

water of crystallization in the sample and was assigned to symmetric and

asymmetric stretching modes of water molecules. The bending mode of

water which is to be expected around 1630cm-1 and the asymmetric

stretching mode of oxalate ion which is expected at 1615cm-1 is overlapped

here to give the very strong peak at 1635.32cm-1.The considerable shift in

frequencies of stretching and bending modes from the free state values3

indicated the presence of hydrogen bonds of medium strengths4. On the basis

of the results available in the literature the very strong peaks at 1321.31cm-1

and weak one at 1364.05 cm-1 were identified as symmetric stretching modes

of CO2 group. The medium band at 490.54 cm-1 and weak one at 618.79 cm-1

were assigned as CO2 wagging modes. The strong band observed at

803.32cm-1 in the spectrum corresponds to the in plane deformation mode of

CO2. The peak at 1364.05cm-1 is assigned as due to symmetric stretching

mode of CO2 or the combinations of the neighbours.5

Extensive IR absorption studies of metallic oxalates 6, 7 proposed that

bands around 800cm-1 and 500cm-1 are due to metal-oxygen bond. The bands

observed at 490.54 cm-1 and 803.32 cm-1 may be considered as overlapping

110 Chapter 5

of metal oxygen bands with modes of oxalate ions. Infrared spectra of rare

earth oxalate crystals are given in the figures 5.8 – 5.15 and IR Spectra data

and vibrational assignments of rare earth oxalate crystals are given in the

tables 5.9 - 5.16 respectively.

Table5.9. IR Spectra data and vibrational assignments of YOx crystal

Wave number cm-1 Intensity Assignment

3357 s/b H2O stretching(sy&asy)

1635.32 v s H-O-H bending /CO2 asy. stretching

1321.31 s CO2 sy.stretching

1364.05 w Combinations

490.54 m CO2 Wagging / M-O bond

618.79 w CO2 Wagging

803.32 s CO2 in plane bend / M-O bond

s-strong, vs-very strong, m-medium, w-weak, v w-very weak b-broad


5. 3 (b) IR spectrum of Yttrium Barium Oxalate crystals

Fig.5.9. IR absorption spectrum of YBaOx crystals

Table 5.10 IR Spectra data and vibrational assignments of YBaOx crystal


3428.54 s/b H2O stretching (sy&asy)

1634.56 v s H-O-H bending / CO2 Asy. stretching



806.69 s CO2 in plane bend/ M-O bond





112 Chapter 5

5.3 (c) IR spectrum of Yttrium Copper Oxalate crystals

Fig.5.10 IR absorption spectrum of YCuOx crystals

Table5.11. IR Spectra data and vibrational assignments of YCuOx crystals



1631.66 v s H-O-H bending / CO2 asy. stretching


1320 s CO2 sy.stretching

809.04 m CO2 in plane bend / M-O bond





5.3 (d) IR spectrum of Yttrium Barium Copper Oxalate crystals

Fig.5.11 IR absorption spectrum of YBaCuOx crystals

Table 5.12. IR Spectra data and vibrational assignments of YBaCuOx crystals



1642.53 v s H-O-H bending / CO2 asy. Stretching





811.13 s CO2 in plane bend / M-O Bond



s-strong ,vs-very strong, m-medium, w-weak, v w-very weak b-broad

114 Chapter 5

5.3 (e). IR spectrum of Praseodymium Barium Copper Oxalate crystals

Fig.5.12 IR absorption spectrum of PrBaCuOx crystals

Table 5.13 IR Spectra data and vibrational assignments of PrBaCuOx crystals



1616.08 v s H-O-H bending / CO2 Asy. Stretching









5.3 (f) IR spectrum of Neodymium Barium Copper Oxalate crystals

Fig.5.13 IR absorption spectrum of NdBaCuOx crystals

Table5.14 IR Spectra data and vibrational assignments of NdBaCuOx crystals



2602.5 w Combination


1605.18 vs H-O-H bending / CO2 Asy. Stretching






116 Chapter 5

5.3 (g) IR spectrum of Gadolinium Barium Copper Oxalate crystals

Fig.5.14 IR absorption spectrum of GdBaCuOx crystals

Table 5.15. IR Spectra data and vibrational assignments of GdBaCuOx crystals


3336.32 s/b H2O stretching(sy&asy)



1616.34 vs H-O-H bending / CO2 Asy. stretching


1318.21 m CO2 sy.stretching

804.54 w CO2 in plane bend / M-O bond




5.3 (h) IR spectrum of Dysprosium Barium Copper Oxalate crystals

Fig.5.15 IR absorption spectrum of DyBaCuOx crystal

Table 5.16. IR Spectra data and vibrational assignments of DyBaCuOx crystals


3338.15 s/b H2O stretching(sy&asy)

1624.04 vs H-O-H bending / CO2 Asy. stretching




488.50 s CO2 Wagging / M-O bond


118 Chapter 5

5.4 Analysis Using Inductively Coupled Plasma Atomic Emission Spectrometer (ICP –AES)

The atomic spectrums emitted by the samples were used to

determine its elemental composition in Inductively Coupled Plasma Atomic

Emission Spectrometer. The wavelength at which emission occurs

identifies the element, quantifies its concentration. The results of the

analysis is given in the Tables 5.17.

Table5.17. Elemental composition of crystals

Concentration ratios R:Ba:Cu (R =Y, Pr, Dy, Gd) Elements

In feed solution Experimental

YBaCuOx 3.3: 1: 1 3.27: .996: .992

PrBaCuOx 3.3: 1: 1. 3.187: 1.05: .990

DyBaCuOx 3.3: 1: 1 3.538: 1.04: .958

GdBaCuOx 3.3: 1: 1 3.22: 1.037: .9626

5.5 Energy dispersive X-ray analysis

Energy dispersive X-ray analysis (EDAX) of the crystals confirmed

the presence of Rare Earth ions, Barium and Copper in the grown crystals.

In EDAX the sample is irradiated with high-energy electrons. The energy

of the radiations emitted by the specimen is related to the number of atoms


of the elements present in the sample. EDAX spectrogram is a curve

plotted between binding energy and the intensity of emitted photoelectron.

The peak heights or areas are a measure of the quantity of the concerned

elements incorporated in the specimen. Though not very accurate, the

comparison of the EDAX peaks of the two elements in a sample gives an

approximate proportion of the elements.

EDAX analyser No. 711, an accessory to the scanning electron

microscope, Philips SEM model 501 was used for the EDAX analysis of

the sample. In the present study each sample was finely powdered and

pellets of 1cm diameter and 1mm thickness were formed using a hydraulic

press by applying pressure of 1.1 ton per cm2. For EDAX, the pellet was

mounted onto an aluminium stub and the surface of the pellet was coated

with gold so as to make good electrical conduction.

120 Chapter 5

5.5.1 EDAX of NdBaCuOx Crystals

The NdBaCuOx crystals were grown by diffusion of 1M solution of

Neodymium Chloride, 0.3M solution of Barium Chloride and 0.3M

solution of Cuprous Nitrate in equal proportion by volume through a gel

column impregnated with 1M Oxalic acid were selected for the

investigation. The EDAX pattern obtained NdBaCuOx crystal is as shown

in the figure 5.16. The elemental incorporation of Nd, Ba and Cu in the

given samples is evident from peaks for these elements. The three peaks

positioned at 5.0 keV, 5.25 keV and 8.01 keV relates to the presence of

Barium, Neodymium and Copper respectively.

Fig 5.16 EDAX pattern of NdBaCuOx


5.5.2 EDAX of YBaCuOx Crystals

The YBaCuOx crystals were grown by gel method. EDAX pattern of

YBaCuOx crystals was taken and it is shown in the Fig.5.17. The elemental

incorporation of Y, Ba and Cu in the given sample is evident from peaks for

these elements. The three peaks positioned at 2 keV, 5.01 keV and 8.02 keV

relates to the presence of Yttrium, Barium and Copper respectively.

Fig. 5.17 EDAX pattern of YBaCuOx

122 Chapter 5

5.6 THERMAL ANALYSIS

The thermal characteristics of the grown crystals were studied using

Perkin Elmer, Diamond TG/DTA. The temperature range selected for the

present study was from ambient temperature to 12000C.

5.6.1 TG / DTA of Yttrium Oxalate Crystals

Fig.5.18 TG /DTA of YOx crystals

Fig.5.18 shows the TG /DTA curve for Yttrium Oxalate Crystals

with chemical formula Y2 (C2O4)3.14 H2O. The thermogram depicts the

decomposition stages of Y2 (C2O4)3.14 H2O crystal with temperature.

Taking the initial weight as standard, the course of decomposition is

analyzed from proportionate weight loss at each stage. The material

started decomposing at about 26.44 0C and the process was completed at


about 5000C at which it is reduced to oxide form. The process of

decomposition involved two very distinct stages. The first stage, which

extends up to 1800C is a dehydration stage and results in the elimination

of all the fourteen water molecules. An endothermic peak centered at

1000C characterizes this. The anhydrous Y2 (C2O4) 3 is unstable and

decomposes during the second stage. The loss of weight around 4320C is

due to two chemical stages; one is related to the release of three CO2

molecules in the temperature range 1800C – 4320C and the other related to

the release of three CO molecules in the temperature range 4320C ─

5000C. At the end of the second stage the sample is reduced to Y2O3, the

corresponding rare earth oxide.

The thermal decomposition mechanism of the grown samples can

be assumed as follows.

20 0

-14H O2 2 4 3 2 2 2 4 326.44 C-180 C

Y (C O ) 14H O Y (C O )→

20 0

-(3CO+3CO )2 2 4 3 2 3180 C-500 C

Y (C O ) Y O→

Results of thermal analysis are given in table 5.18. The observed

mass loss and calculated mass loss in both stages are tallied.

124 Chapter 5

Table 5.18. Thermal analysis results of Y2 (C2O4)3.14H2O crystals

Decomposition

Temp. 0C

Loss of

material Observed

mass loss % Calculated

mass loss % Nature of

reaction

26.44 -180 14 H2O 36.3700 36.3210 Endo dehydration

180 -500 3CO2+3CO 31.0080 31.1320 Endo decomposition

5.6.2 TG / DTA of Yttrium Barium Oxalate Crystals.

Fig.5.19 TG /DTA of YBaOx crystals

Fig. 5.19 shows the TG /DTA curve for Yttrium Barium Oxalate

Crystals with chemical formula Y2Ba (C2O4)4.8H2O. The thermogram

depicts the decomposition stages of crystal Y2Ba (C2O4)4. 8H2O with

temperature. Taking the initial weight as standard, the course of


decomposition is analyzed from proportionate weight loss at each stage.

The material started decomposing at about 38.08 0C and the process was

completed at about 5000C at which it was reduced to oxide form. The

process of decomposition involves two very distinct stages. The first stage,

which extends up to 116.420C is a dehydration stage and results in the

elimination of all the eight water molecules. An endothermic peak centered

at 92.210C characterizes this. The anhydrous Y2Ba (C2O4)4 is unstable and

decomposes during the second stage. The loss of weight around 434.050C is

due to two chemical stages, one is related to the release of four CO

molecules in the temperature range 116.420C – 421.230C and the other

related to the release of four CO2 molecules in the temperature range

421.230–5000C that are endothermic in character with endothermic peaks

centered at 421.230C and 434.050C respectively. At the end of the second

stage the sample is reduced to Y2BaO4, the corresponding rare earth oxide.


be assumed as follows.

20 0-8H O

2 2 4 4 2 2 2 4 438.08 C-116.42 CY Ba(C O ) 8H O Y Ba(C O )→

2

0 0-(4CO+4CO )

2 2 4 4 2 2 4 4116.42 C - 500 CY Ba(C O ) Y Ba(C O )→

126 Chapter 5



Table 5.19. Thermal analysis results of Y2Ba (C2O4)4. 8H2O crystals

Decomposition Temp.0C

Loss of material

Observed mass loss %

Calculated mass loss %

Nature of reaction

38.08 -116.42 8 H2O 16.7358 17.7520 Endo dehydration

116.42 -500 4CO2+4CO 35.3840 35.5047 Endo

decomposition

5.6.3 TG / DTA of Yttrium Copper Oxalate Crystals.

Fig.5.20 TG /DTA of YCuOx crystals

Fig.5.20 shows the TG /DTA curve for Yttrium Copper Oxalate

Crystals with chemical formula Y2Cu (C2O4)4.7 H2O. The thermogram


depicts the decomposition stages of crystal Y2Cu (C2O4)4.7 H2O with

temperature. Taking the initial weight as standard, the course of

decomposition was analyzed from proportionate weight loss at each stage.

The material started decomposing at about 35.830C and the process was

completed at about 533.330C at which it was reduced to oxide form. The

process of decomposition involves two very distinct stages. The first stage,

which extends up to 100.780C is a dehydration stage and results in the

limination of all the seven water molecules. An endothermic peak centered

at 100.780C characterizes this. The anhydrous Y2Cu (C2O4)4 is unstable and

decomposes during the second stage. The loss of weight around 434.59 0C

is due to two chemical stages, one is related to the release of four CO

molecules in the temperature range 100.78 0C – 416.67 0C and the other

related to the release of four CO2 molecules 416.67 0C – 533.34 0C. At the

end of the second stage the sample is reduced to Y2CuO4, the


The thermal decomposition mechanism of the grown samples can be

assumed as follows.

20 0-7 H O

2 2 4 4. 2 2 2 4 435.83 C - 100.75 CY Cu(C O ) 7H O ( )Y Cu C O→

20 0

-(4CO+4CO )2 2 4 4 2 4100.75 C-533.34 C

Y Cu (C O ) Y CuO→

128 Chapter 5


mass loss and calculated mass loss in both stages show only a slight

difference.

Table 5.20. Thermal analysis results of Y2 Cu (C2O4)4.7 H2O crystals

Decomposition Temp. 0C

Loss of material



Nature of reaction

35.83 -100.78 7 H2O 17.5153 16.6378 Endo dehydration

100.78 -533.34 4CO2+4CO 40.0350 39.999 Endo

decomposition

5.6.4 TG / DTA of Yttrium Barium Copper Oxalate Crystals.

Fig.5.21 TG /DTA of YBaCuOx crystals


Fig.5.21 shows the TG /DTA curve for Yttrium Barium Copper

Oxalate Crystals with chemical formula Y2BaCu(C2O4)5.8H2O. The

thermogram depicts the decomposition stages of crystal

Y2BaCu(C2O4)5.8H2O with temperature. Taking the initial weight as

standard, the course of decomposition was analyzed from proportionate

weight loss at each stage. The material started decomposing at about

35.980C and the process was completed at about 5360C at which it was

reduced to oxide form. The process of decomposition involves two very

distinct stages. The first stage, which extends up to 1210C is a dehydration

stage and results in the elimination of all the eight water molecules. This is

characterized by an endothermic peak centered at 108.370C. The anhydrous

Y2BaCu (C2O4)5 is unstable and decomposes during the second stage. The

loss of weight around 5000C is due to two chemical stages, one is related to

the release of five CO molecules in the temperature range 1210C – 4010C

and the other related to the release of five CO2 molecules in the temperature

range 4010C – 5360C. At the end of the second stage the sample is reduced

toY2BaCuO5, the corresponding rare earth oxide.


assumed as follows.

130 Chapter 5

20 0

-8 H O2 2 4 5. 2 2 2 4 535.98 C - 121 C

Y BaCu(C O ) 8H O Y BaCu(C O )→

20 0

-(5 CO+5CO )2 2 4 5 2 5121 C - 536 C

Y BaCu(C O ) Y BaCuO→



Table 5.21. Thermal analysis results of Y2BaCu (C2O4)5 .8H2O crystals

Decomposition

Temp. 0C

Loss of

Material

Observed mass loss

%


Nature of reaction

35.98 - 121 8 H2O 14.9950 14.9500 Endo dehydration

121 - 536 5CO2+5CO 37.7750 37.3940 Endo decomposition

5.6.5 TG / DTA of Praseodymium Barium Copper Oxalate Crystals.

Fig.5.22 TG /DTA of Pr BaCuOx crystals


Fig.5.22 shows the TG /DTA curve for Praseodymium Barium

Copper Oxalate Crystals with chemical formula Pr2BaCu(C2O4)5.9H2O. The

thermogram depicts the decomposition stages of crystal Pr2BaCu(C2O4)5.9H2O

with temperature. Taking the initial weight as standard, the course of

decomposition is analyzed from proportionate weight loss at each stage. The

material started decomposing at about 45.740C and the process was completed at

about 5700C at which it was reduced to oxide form. The process of

decomposition involves two very distinct stages. The first stage, which extends

up to 1250C is a dehydration stage and results in the elimination of all the nine

water molecules. An endothermic peak centered at 124.560C characterizes this.

The anhydrous Pr2BaCu (C2O4)5 is unstable and decomposes during the second

stage. Loss of weight in the temperature range 1250C– 5700C relates to the

release of five molecules of CO and CO2 that is endothermic in character with

endothermic peak centered at 564.52 0C. At the end of the second stage the

sample is reduced to Pr2BaCuO5, the corresponding rare earth oxide.


assumed as follows.

20 0

-9 H O2 2 4 5. 2 2 2 4 545.74 C - 125 C

Y BaCu(C O ) 9H O Y BaCu(C O )→

20 0

-(5CO+5CO )2 2 4 5 2 5125 C - 270 C

Pr BaCu(C O ) Pr BaCuCuO→

132 Chapter 5



difference.

Table 5.22. Thermal analysis results of Pr2BaCu (C2O4)5.9 H2O crystals


Loss of material



Nature of reaction

45.74 -125 9H2O 15.4369 14.9349 Endo dehydration


5.6.6 TG / DTA of Neodymium Barium Copper Oxalate Crystals.

Fig.5.23 TG /DTA of NdBaCuOx crystals


Fig.5.23 shows the TG /DTA curve for Neodymium Barium Copper

Oxalate Crystals with chemical formula Nd2BaCu (C2O4)5.12 H2O. The

thermogram depicts the decomposition stages of crystal, Nd2BaCu

(C2O4)5.12H2O with temperature. Taking the initial weight as standard, the

course of decomposition was analyzed from proportionate weight loss at

each stage. The material started decomposing at about 39.57 0C and the

process was completed at about 7150C at which it was reduced to oxide

form. The process of decomposition involves two very distinct stages. The

first stage, which extends up to 2050C is a dehydration stage and results in

the elimination of all the twelve molecules of water. The loss of weight

around 2050C is due to two chemical stages; one is related to the release of

nine molecules of water in the temperature range.

39.570C -1500C and the other related to the release of three

molecules of water in the temperature range 1500C – 2050C. Endothermic

peaks centered at 112.910C and at 204.950C respectively characterize these.

The anhydrous Nd2BaCu (C2O4)5 unstable and decomposes during the

second stage. The loss of weight around 4100C is due to two chemical

stages, one is related to the release of five CO molecules in the temperature

range 2050C - 4200C and the other related to the release of five CO2

134 Chapter 5

molecules 4200C - 7150C. At the end of the second stage the sample is

reduced toNd2BaCuO5, the corresponding rare earth oxide.


assumed as follows.

20 0

-12 H O2 2 4 5 2 2 2 4 539.57 C -205 C

Nd BaCu (C O ) .12 H O Nd BaCu (C O )→

20 0

- (5CO+5CO )2 2 4 5 2 5205 C - 715 C

Nd BaCu (C O ) Nd BaCuO→



difference.

Table 5.23.Thermal analysis results of Nd2BaCu (C2O4)5.12 H2O crystals


Loss of material



Nature of reaction

39.57 - 205 12H2O 18.9201 18.8589 Endo dehydration



5.6.7 TG / DTA of Gadolinium Barium Copper Oxalate Crystals.

Fig.5.24 TG /DTA of GdBaCuOx crystals

Fig.5.24 shows the TG /DTA curve for Gadolinium Barium

Copper Oxalate Crystals with chemical formula Gd2BaCu(C2O4)5.13H2O.

The thermogram depicts the decomposition stages of crystal Gd2BaCu

(C2O4)5.13 H2O with temperature. Taking the initial weight as standard,

the course of decomposition was analyzed from proportionate weight loss

at each stage. The material started decomposing at about 39.370C and the


form. The process of decomposition involves two very distinct stages.

The first stage, which extends up to 2350C is a dehydration stage and

results in the elimination of all the thirteen water molecules. Endothermic

136 Chapter 5

peaks centered at 91.190C and at 218.020C characterize this. The

anhydrous Gd2BaCu (C2O4)5 is unstable and decomposes during the

second stage. The second stage, which extends up to 8150C is a

decomposition stage and results in the elimination of five molecules of

CO and five molecules of CO2 in the temperature range 2350C – 815 0C.

At the end of the second stage the sample is reduced to Gd2BaCuO5, the



be assumed as follows

20 0

-13H O2 2 4 5 2 2 2 4 539.37 C -235 C

Gd BaCu (C O ) .13 H O Gd BaCu (C O )→

20 0

- (5CO+5CO )2 2 4 5 2 5235 C - 815 C

Gd BaCu (C O ) Gd BaCuO→




Table 5.24. Thermal analysis results of Gd2BaCu (C2O4)5.13 H2O crystals


Loss of material

Observed mass loss

%


Nature of reaction

39.37 - 235 13 H2O 19.6360 19.6740 Endo dehydration

235 –815 5CO2+5CO 30.9670 30.2676 Endo

decomposition

5.6.8 TG / DTA of Dysprosium Barium Copper Oxalate Crystals.

Fig.5.25 TG /DTA of DyBaCuOx crystals

Fig.5.25 shows the TG /DTA curve for Dysprosium Barium Copper

Oxalate Crystals with chemical formula Dy2BaCu(C2O4)5.12H2O. The

thermogram depicts the decomposition stages of crystal Dy2BaCu

138 Chapter 5

(C2O4)5.12 H2O with temperature. Taking the initial weight as standard, the

course of decomposition was analyzed from proportionate weight loss at

each stage. The material started decomposing at about 39.54 0C and the


form. The process of decomposition involves two very distinct stages. The

first stage, which extends up to 2050C is a dehydration stage and results in

the elimination of all the twelve water molecules. Endothermic peaks

centered at 85.890C and 177.240C characterize this. The anhydrous Dy2BaCu

(C2O4)5 is unstable and decomposes during the second stage. The second

stage which extends up to 7800C is a decomposition stage and results in the

elimination of five molecules of CO and five molecules of CO2 in the

temperature range 2050C – 7800C. At the end of the second stage the sample

is reduced to Dy2BaCuO5, the corresponding rare earth oxide.


assumed as follows

20 0

-12 H O2 2 4 5 2 2 4 539.54 C -205 C

Dy BaCu (C O ) .12 H2O Dy BaCu (C O ) →

20 0

- (5CO+5CO )2 2 4 5 2 5205 C -780 C

Dy BaCu (C O ) Dy BaCuO →




difference.

Table 5.25. Thermal analysis results of Dy2BaCu (C2O4)5.12 H2O crystals


Loss of material



Nature of reaction

39.54 -205 12 H2O 17.9530 18.2760 Endo dehydration

205 -780 5CO2+5CO 30.4105 30.4597 Endo

decomposition

5.7 Differential scanning calorimetry (DSC)

Differential scanning calorimetry (DSC) is a thermoanalytical

technique in which the difference in the amount of heat required to increase

the temperature of a sample and reference are measured as a function of

temperature. In the present study DSC curve was recorded by using Mettler

Toledo DSC 822e.at the sampling rate of Max 10 values /sec in the

temperature range of -150 0C to7000C. DSC measures the amount of heat

energy absorbed or released by a sample, as it is heated or cooled or held at

constant temperature. For DSC analysis, Non – explosive, non –corrosive

samples, about 10–50 mg are required.

140 Chapter 5

5.7.1 DSC Analysis of Yttrium Oxalate Crystals

Fig.5.26. DSC analysis of YOx crystals

Fig.5.26 shows the DSC curve for Yttrium Oxalate Crystals with

chemical formula Y2 (C2O4)3.14 H2O. The curve depicts the decomposition

stages of Y2 (C2O4)3.14 H2O crystals with temperature. The endothermic

peak at 133.360 C relates to the loss of water of crystallization and

endothermic peak at 434.430 C is characterized due to the release of CO

and CO2.


57.2 DSC Analysis of Yttrium Barium Oxalate Crystals

Fig.5.27. DSC analysis of YBaOx crystals

Fig.5.27 shows the DSC curve for Yttrium Barium Oxalate Crystals

with chemical formula Y2Ba(C2O4)4.8H2O. The curve depicts the

decomposition stages of Y2Ba (C2O4)4.8H2O crystals with temperature. The

endothermic peak at 110.700C relates to the loss of water of crystallization

and endothermic peaks at 240.390C, 371.520 C and 435.960 C are due to the

release of four molecules of CO and four molecules of CO2.

142 Chapter 5

5.7.3 DSC Analysis of Yttrium Copper Oxalate Crystals

Fig.5.28. DSC analysis of YCuOx crystals

Fig.5.28 shows the DSC curve for Yttrium Copper Oxalate Crystals

with chemical formula Y2Cu(C2O4)4.7H2O. The curve depicts the

decomposition stages of Y2Cu(C2O4)4.7H2O crystals with temperature. The

endothermic peak at 102.730C relates to the loss of water of crystallization

and endothermic peaks at 177.930C, 360.400C and 425.600C are due to the

release of four molecules of CO and four molecules of CO2.


5.7.4 DSC Analysis Of Yttrium Barium Copper Oxalate Crystals

Fig.5.29 DSC analysis of YBaCuOx crystals

Fig.5.29 shows the DSC curve for Yttrium Barium Copper Oxalate

Crystals with chemical formula Y2BaCu(C2O4)5.8H2O. The curve depicts

the decomposition stages of Y2BaCu(C2O4)5.8H2O crystals with

temperature. The endothermic peak at 102.730C relates to the loss of

water of crystallization and endothermic peaks at 227.520C, 433.550C and

523.750C are due to the release of five molecules of CO and five

molecules of CO2.

144 Chapter 5

5.7.5 DSC Analysis of Praseodymium Barium Copper Oxalate Crystals

Fig.5.30 DSC analysis of PrBaCuOx crystals

Fig.5.30 shows the DSC curve for Praseodymium Barium Copper

Oxalate Crystals with chemical formula Pr2BaCu(C2O4)5.9 H2O. The curve

depicts the decomposition stages of Pr2BaCu(C2O4)5.9H2O crystals with

temperature. The endothermic peak at 163.390C relates to the loss of water

of crystallization and endothermic peaks at 224.97 0Cand 402.58 0C are due

to the release of five molecules of CO and five molecules of CO2.


5.7.6 DSC Analysis of Neodymium Barium Copper Oxalate Crystals

Fig.5.31 DSC analysis of NdBaCuOx crystals

Fig.5.31 shows the DSC curve for Neodymium Barium Copper

Oxalate Crystals with chemical formula Nd2BaCu(C2O4)5.12H2O. The

curve depicts the decomposition stages of Nd2BaCu(C2O4)5.12H2O crystals

with temperature. The endothermic peaks at 1480C and 174.170C relate to

the loss of twelve molecules of water. The endothermic peaks at 261.190C

and 408.39 0C are due to the release of five molecules of CO and five

molecules of CO2.

146 Chapter 5

5.7.7 DSC Analysis of Gadolinium Barium Copper Oxalate Crystals

Fig.5.32 DSC analysis of GdBaCuOx crystals

Fig.5.32 shows the DSC curve for Gadolinium Barium Copper

Oxalate Crystals with chemical formula Gd2BaCu(C2O4)5.13H2O. The

curve depicts the decomposition stages of Gd2BaCu(C2O4)5.13H2O crystals

with temperature. The endothermic peaks at 134.13 0C and 197.14 0C relate

to the loss of thirteen molecules of water. The endothermic peaks at 275.35

0C and 434.63 0C are due to the release of five molecules of CO and five

molecules of CO2


5.7.8 DSC Analysis of Dysprosium Barium Copper Oxalate Crystals

Fig.5.33 DSC analysis of DyBaCuOx crystals

Fig.5.33 shows the DSC curve for Dysprosium Barium Copper

Oxalate Crystals with chemical formula Dy2BaCu (C2O4)5.12H2O.. The

curve depicts the decomposition stages of Dy2BaCu(C2O4)5.12H2O crystals

with temperature. The endothermic peaks at 131.110C and 219.290C relate

to the loss of twelve molecules of water. The endothermic peaks at

266.030C, 365.400C and 434.520C are due to the release of five molecules

of CO and five molecules of CO2.

148 Chapter 5

5.8 CONCLUSION

X-ray powder diffraction analyses of the grown crystals provided

their lattice parameters. It was observed that all the grown crystals are in

the tetragonal system. FT-IR studies showed the presence of various

functional groups. IR studies confirmed the presence of water of

crystallization and oxalate group in the rare earth mixed oxalate crystals.

The thermal analysis data supported the structural formula for the rare earth

mixed oxalate crystals. DSC measured the amount of heat energy absorbed

or released by the rare earth mixed oxalate crystals, as it is heated, cooled

or held at a constant temperature. Complementary results were obtained

for decomposition and dehydration reactions in both TG/DTA and DSC

studies. Rare Earth, Barium and Copper in the samples were analysed by

Inductively Coupled Plasma Atomic Emission Spectrometer (ICP –AES)

and Energy Dispersive Analysis by X-rays (EDAX).


5.9 REFERENCES

1 Hansson E., Acta. Chem. Scand., 24 (1970) 2969.

2 Ollendorff W. and F. Weigel, Inorg. Nucl.Chem. Letters, 5 (1969) 263.

3 Mathew X., Suresh G., Pradeep T. and Nayer V. U., J. Raman

Spectroscopy, 21 (1990)279.

4 Vinogradov S. N. and Linnell R. H., Hydrogen Bonding, Von

Nostrand Rein hold, New York, 1971.

5 Petrosv I. and Soptrajanov B., Spectrochimica Acta, 31A(1975) 309.

6 Fujitha J., Martell A. E. and Nakamoto K. J.Chemical Physics , 36

(1962).

7 Gibson J.K. and N.A., Thermo chemical Acta, 226 (1993)301.

8 Wendlandt W.W., Thermal Methods of Analysis, 2 nd Edn. Wiley,

New York, 1974.

9 Mahadeo, A. Nabar and V. R. Ajgaokar., Less- Common Metals, 106

(1985)211.

10 Pope M.I., and Judd M. D., Differential Thermal Analysis, Hedyden,

Philadelphia, 1977.

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