SOL-GEL SYNTHESIS, CRYSTAL STRUCTURE, MAGNETIC,

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Transcript of SOL-GEL SYNTHESIS, CRYSTAL STRUCTURE, MAGNETIC,

ELECTRONIC AND OPTICAL PROPERTIES IN Bi2+xAxD4-3xO7+δ
(A=Al, Ce, Yb, Ga; D=Ni, Pd) NANOCOMPOSITE OXIDES
Thesis
for the award of the degree of
DOCTOR OF PHILOSOPHY
Dedicated to my beloved Family, Friends &
Teachers
i
Department of Chemistry Pondicherry University R. Venkatraman Nagar
Kalapet Puducherry - 605 014. India
Tel: 091-413-2654413, ext. 413 (O) Email: [email protected]
_______________________________________________________________________
CERTIFICATE
This is to certify that the thesis entitled “SOL-GEL SYNTHESIS, CRYSTAL
STRUCTURE, MAGNETIC, ELECTRONIC AND OPTICAL PROPERTIES IN
Bi2+xAxD4-3xO7+δ
(A=Al, Ce, Yb, Ga; D=Ni, Pd) NANOCOMPOSITE OXIDES”
submitted to Pondicherry University, for the award of the degree of Doctor of Philosophy
is a bonafide record of research work carried out by Ms. M. Yogapriya, in the
Department of Chemistry, Pondicherry University, Puducherry - 605 014, India, under
my guidance and supervision. This is to certify that the thesis represents his independent,
original work without forming previously any part of the material for the award of any
degree, diploma or any other similar title in any University.
Puducherry (Dr. Bidhu Bhusan Das)
Date: 25.06.2012 Supervisor
I hereby declare that the thesis entitled “SOL-GEL SYNTHESIS, CRYSTAL
STRUCTURE, MAGNETIC, ELECTRONIC AND OPTICAL PROPERTIES IN
Bi2+xAxD4-3xO7+δ
(A=Al, Ce, Yb, Ga; D=Ni, Pd) NANOCOMPOSITE OXIDES”
submitted to the Pondicherry University, Puducherry, India, in partial fulfillment of the
requirements for the award of the degree of Doctor of Philosophy is the original and
independent work carried out by me, in the Department of Chemistry, under the
supervision of Dr. Bidhu Bhusan Das, Professor, Department of Chemistry, Pondicherry
University, Puducherry. I also declare that this work, in part or full, has not formed the
basis for the award of any degree, diploma, or any other similar titles.
Puducherry (M. Yogapriya)
iii
ACKNOWLEDGEMENT Many people have helped me accomplish this dissertation, and I owe my gratitude
to all of them. First and foremost I would like to express my sincere gratitude to Dr. Bidhu
Bhusan Das, Professor and Head, Department of Chemistry, Pondicherry University, without whose guidance and advice this dissertation would not be what it is today. His constant encouragement during the course of the research work and invaluable guidance with patient rescued me from despair on countless occasions. I express my heartfelt gratitude to my Doctoral Committee members Prof. Late. P. Sambasiva Rao, Department of Chemistry and Dr. S. Sivaprakasam, Department of Physics, Pondicherry University for offering their expertise throughout the period of research work. I am indebted to Dr. H. Surya Prakash Rao, Professor and Dean, School of Physical, Chemical and Applied Sciences, Dr. Late. P. Sambasiva Rao, Department of Chemistry and other faculty members Dr. K. Anbalagan, Dr. K. Tharanikkarasu, Dr. R. Venkatesan, Dr. Bala. Manimaran, Dr. G. Vasuki, Dr. K. Bakthadoss, Dr. C Sivasankar, Dr. N. Dastagiri Reddy, Dr. M.M. Balakrishnarajan and Dr. C.R. Ramanathan, Dr. Binoy Krishna Saha, Dr. S. Sabiah, Dr. Toka Swu and Dr. R. Padmanaban, Department of Chemistry, Pondicherry University for their encouragement. I especially thanks to Dr. M.M. Balakrishnarajan providing softwares to proceed the theoretical calculations. I remit my thanks to all the office staff for their help. I thank Mr. Gugan and all non- teaching staff members of the Department of Chemistry for their help. I am much obliged to Dr. M.J. Nilges, Assistant Director, Illinois EPR Research Centre, Illinois, USA, for his assistance with EPR data of the samples at 5 K. My grateful thanks to Prof. M.S. Pandian, Department of Earth Science, Prof. K. Porsezian and Prof. G. govindaraj, Department of Physics, Pondicherry University who extended the helping hands to record XRD of the samples. I wish to thank SAIF, I.I.T Madras in recording the DSC/TGA/DTA traces of samples. I wish to express my thanks to Head, Technicians and Staff members of Central
Instrumental Facility, Pondicherry University, Er. S. Ramasamy, Technical Officer, Mr. Elumalai, Mr. Gopalakrishnan, and Ms Elisa, CIF, Pondicherry University, in recording the Thermal studies, UV-vis spectra, VSM, SEM and EDX data.
iv
I thank all my lab-mates Dr. R.K. Sharma, Dr. A. Srinivassan, Mr. S. Ramesh, Mr. K. Palanisamy, Mr. Govinda Rao, Mr. Chandru, Mr. Jubin Jose, Mr. P.A.M. Ziyad, Mr. Muthuraj, Mr. Thangaraj, Mrs. K. Sumathi, Mr. D. Prabhu, Mr. Umer Rafiq, Mr. Guru doss Gupta and M.Sc students for their help.
I thank all Research Scholars in Department of Chemistry, Mr. E. Gnanamani and Mr. Suman Bhattacharya for their moral support and help and Mr. S. Boobalan, Mr. K.Velavan, Mr. K. Parthiban, Ms. P. Manochitra, Ms. S. Ramachitra and P. Sathiya from the EPR research group for their help in recording EPR Spectra. Mr. Venkat Ramaiah and Mr. Namitharan for recording DRS Spectra, Ms. P. Muthu Austeria from Chemical Information Sciences lab, Mrs. Maharaja mahalakshmi, Mr. Ganesh, Mr. Manjunathan, Mr. Thirumurugan from photochemistry laboratory Mr. K. Bakthavachalam, Ms. K. Maheswari, Mr. N.M. Rajendiran from Dr.NDR lab, Mr. S. Karthikeyan and Mr. M. Karthikeyan from Dr. B.M. lab, Mr. A. Parthiban from Dr. H.S.P. lab for their help. I would like to thank the helping hands from department of physics Mrs. R. Elillarassi and Mr. Panneer Muthuselvam for their help.
Despite all the support and help I have received, I am solely responsible for any mistakes herein.
I would like to say big thank-you to Mr. K. Balaraman for being supportive and helping me throughout my Ph. D work.
I wish to express my sincere love to all my friends Manamathi, Indhumathi, Rama, Mano, Ponni, Radhika, Austeria, Kamakshi, Kalai, Supriya, Maya, Poorni, Shalini, Revathi for their love, being supportive and patient and for giving me company while I toiled hard.
My heartfelt thank to my all teachers and well wishers for their moral support. I also wish to express my appreciation to my sister Ms. Lakshmidevi and brother
Mr. Vinothraj for their thoughtful care and concerns for me. Last, but certainly not least, I am forever grateful to my parents for showing me
the value of education. My deepest thanks go to my mom for supporting and encouraging me to achieve and be successful.
(M. Yogapriya)
Figure Captions
Fig. 3.1. Flowchart of the synthetic strategy of the samples in the series of Bi2+xAxD4-3x
O7+ δ
Fig. 4.1 Powder XRD indexed pattern of the system Bi
(A=Al, Ce, Yb & Ga; D=Ni & Pd) nanocomposite oxide
2+xAlxNi4-3xO7+δ
0.25, 0.50, 0.75)
(A1-A4: x=0,
Fig. 4.2.1 (a) SEM micrograph at 2 µm magnification and (b) EDX profile of Bi2Ni4O7
Fig. 4.2.2 (a) SEM micrograph at 2 and 5 µm magnifications and (b) EDX profile of
(A1) with compositions of the elements in randomly selected grain.
Bi2.25Al0.25Ni3.25O7
(A2) with compositions of the elements in randomly
Fig. 4.2.3 (a) SEM micrograph at 2 µm magnification and (b) EDX profile of
Bi2.5Al0.5Ni2.5O7
(A3) with compositions of the elements in randomly
Fig. 4.2.4 (a) SEM micrograph at 2 and 1 µm magnification and (b) EDX profile of
Bi2.75Al0.75Ni1.75O7
(A4) with compositions of the elements in randomly
Fig. 4.4.1(a) Perspective view of the unitcell of A1 (Bi8Ni16O28), (b) A2
(Bi9Al1Ni13O28
)
Fig. 4.4.2 (e-h) 2-dimensional view on (111) plane of Bi2+xAlxNi4-3xO7+δ
0.25, 0.50, 0.75)
(A1-A4: x=0,
respectively
(A1-A4: x=0, 0.25, 0.50, 0.75)
Fig. 4.4.4 (a-d) 3-dimensional electron density from (010) plane of Bi2+xAlxNi4-3xO7+δ
Fig. 4.4.5 2-dimensional electron density contour on (010) plane of Bi
(A1-A4: x=0, 0.25, 0.50, 0.75) respectively
8Ni16O28
showing the symmetric positions of Ni and O atoms on the plane.
(A1-A4)
poly crystalline system at room temperature
(A1-A4: x=0, 0.25, 0.50, 0.75) of
Fig. 4.6.1 (a) band structure (b) density of states of Bi2Ni4O7 (A1); (c) band structure (d)
vi
density of States of Bi2.75Al0.75Ni1.75O7
Fig. 4.6.2 partial density of states of individual atoms of Bi, Al, Ni, O of
(A4)
Bi2.75Al0.75Ni1.75O7
Fig. 4.7 (a) EPR spectra at 300 K for a polycrystalline samples Bi
(A4)
(A1-
Fig. 4.7 (b) EPR spectra at 77 K for a polycrystalline samples Bi2+xAlxNi4-3xO7+δ
x=0, 0.25, 0.50, 0.75) respectively
(A1-
A4:
Fig. 4.7 (c) EPR spectra at 6 K for a polycrystalline samples Bi2.0Ni4.0O7
Bi
2.5Al0.5Ni2.5O7
Fig. 4.8. (a) Magnetic hysteresis loops of A1-A4 at 300 K . This show the soft ferro
(A3)
magnetic nature. (b) shows an expanded scale of the nominal composition
x=0 (A1). (c) The upper left inset shows the zoom in the low applied field
regime.
Fig. 4.9 (a) UV – vis DRS spectra of compositions Bi2+xAlxNi4-3xO7+δ
x=0, 0.25, 0.50, 0.75) respectively
(A1-A4:
Fig. 4.9 (b) Band gap values of A1-A4 obtained by plotting (αhν)2
Fig. 5.1 Powder XRD- pattern of Bi
vs. hν.
2+xCexNi4-3xO7+δ
Fig. 5.2.1 (a) SEM micrograph at 10 µm magnification and (b) EDX profile of
(x = 0.25, 0.50, 0.75, 1.0) (B1-B4)
Bi2.25Ce0.25Ni3.25O7
(B1) with compositions of the elements in randomly
Fig. 5.2.2 (a) SEM micrograph at 10 µm magnification and (b) EDX profile of B2 with
compositions of the elements in randomly selected grain.
Fig. 5.2.3 (a) SEM micrograph at 10 µm magnification and (b) EDX profile of B3 with
compositions of the elements in randomly selected grain.
Fig. 5.2.4 (a) SEM micrograph at 10 µm magnification and (b) EDX profile of B4 with
compositions of the elements in randomly selected grain.
Fig. 5.3 TGA/DTA/DSC traces of Bi2+xCexNi4-3xO7
Fig. 5.4.1 (a-d) Perspective view of the unitcell of B1-B4
(x = 0.25, 0.50, 0.75, 1.0) (B1-B4)
Fig. 5.4.2 (a) 001 plane; (b) 111 plane; (c) asymmetric unit of B1
Fig. 5.4.3 (a) 001 plane; (b) 111 plane of B2
vii
Fig. 5.4.4 (a) 001 plane; (b) 111 plane; (c) asymmetric unit of B3
Fig. 5.4.5 (a) 001 plane; (b) 111 plane; (c) asymmetric unit of B4
Fig. 5.4.6 3-dimensional electron density from (010) plane of (c) B3; (d) B4
Fig. 5.4.7 2-dimensional electron density contour on (010) plane of (a-d) B1-B4
showing the symmetric positions of Ni and O atoms on the plane.
Fig. 5.5.1 (a) band structure (b) density of states of B1; (c) band structure (d) density of
states of B2
Fig. 5.5.1 (e) Band structure (f) density of states of B3; (g) band structure (h) density of
states of B4
Fig. 5.5.2 Partial density of states of individual atoms Bi, Ce, Ni and O of B4
Fig. 5.6 (a) EPR spectra of Bi2+xCexNi4-3xO7+δ
Fig. 5.6 (b) EPR spectra of Bi
(x= 0.25, 0.50, 0.75, 1.0) (B1-B4) at 300
K
2+xCexNi4-3xO7+δ
Fig. 5.7 M vs H plot showing weak hysteresis loop for B1-B4
(x = 0.25, 0.50, 0.75, 1.0) (B1-B4) at 77
K
Fig. 5.8 (a) Optical absorption spectra of Bi2+xCexNi4-3xO7+δ
(B1- B4)
Fig 5.8 (b) Variation of (αhν)2
Calculated extrapolating the curve.
as a function of energy (hν) of B1-B4. Band gap energy is
Fig. 6.1 powder X-ray diffraction pattern of C1-C4
Fig. 6.2 (a-d) SEM micrographs of C1-C4
Fig.6.2.2 (a-b) EDX profile of C1 and C2
Fig.6.2.2 (c-d) EDX profile of C3 and C4
Fig. 6.3 TGA/DTA/DSC traces of C1-C4
Fig. 6.4.1 (a-d) Perspective view of unitcell structure of C1-C4
Fig. 6.4.2 (a-d) 2-dimensional view on (001) plane of C1-C4
Fig. 6.4.3 (a-d) Asymmetric unit of C1-C4
Fig. 6.4.4 (a-d) 3-dimensional electron density from (010) plane of C1-C4
Fig. 6.4.5 2-dimensional electron density contour on (010) plane of C1-C4 showing the
symmetric positions of Bi, Pd and O atoms on the plane.
Fig. 6.5.1 (a) band structure (b) density of states of C1; (c) band structure (d) density of
viii
states of C2
Fig. 6.5.1 (e) band structure (f) density of states of C3; (g) band structure (h) density of
states C4
Fig. 6.5.2 Partial density of states of individual atoms of Bi, Pd, Yb and O of C1 and C4
Fig. 6.6 (a) EPR spectra at 300 K of C1-C4
Fig. 6.6 (b) EPR spectra at 77 K of C1-C4
Fig. 6.7.1 Magnetic hysteresis loops of C1-C4 at 300 K
Fig. 6.8 (a) Observed optical absorption spectra of C1-C4
Fig. 6.8 (b) Band gap energy calculation by plotting (αhν)2
Fig. 7.1 Powder XRD patterns of Bi
vs. hν
2+xGaxPd4-3xO7+δ
at different magnifications
0.60)
Fig. 7.4.1 Perspective view of the unitcell of Bi
(D1-D4: x=0.15, 0.30, 0.45, 0.60)
2+xGaxPd4-3xO7+δ
(D1-D4: x=0.15, 0.30,
Fig. 7.4.2 2-dimensional view on (001) plane of Bi2+xGaxPd4-3xO7+δ
0.30, 0.45 & 0.60) respectively
0.60) respectively
(D1-D4: x=0.15, 0.30, 0.45 &
Fig. 7.4.4 (a-d) 3-dimensional electron density from (001) plane of Bi2+xGaxPd4-3xO7+δ
(D1-D4: x=0.15, 0.30, 0.45 & 0.60)
Fig. 7.4.5 (a-d) 2-dimensional electron density contour on (010) plane of Bi2+xGaxPd4-3x
O7+δ
Fig. 7.5.1 (a) band structure (b) density of states of D1; (c) band structure (d) density of
(D1-D4: x=0.15, 0.30, 0.45 & 0.60) respectively
States of D2
Fig. 7.5.1 (e) band structure (f) density of states of D3; (g) band structure (h) density of
States of D4
Fig. 7.5.2 Partial Density of states of Bi, O, Ga, Pd in D4
Fig. 7.6.1 EPR spectra at 300 K of D1-D4 respectively
Fig. 7.6.2 EPR spectra at 77 K of D1-D4 respectively
ix
Fig. 7.6.3 EPR spectra shows the zoom in the field around 3000 G at 77 K of D1
and D2 respectively
Fig. 7.7 Magnetic hysteresis loops of D1-D4 at 300 K
Fig. 7.8 (a) Observed optical absorption spectra of D1-D4
Fig. 7.8 (b) Band gap energy of D1-D4 obtained by plotting (αhν)2
vs. hν
List of Tables
Table 3.1 Compositions of samples in the series of Bi2+xAxD4-3xO7+ δ
D=Ni, Pd) nanocomposite oxide
(A=Al, Ce, Yb, Ga;
Table 4.1 Unit cell parameters, calculated and observed densities and average crystallite
sizes in A1-A4 of Bi2+xAlxNi4-3xO7+δ
Table 4.4.1 Unit cell dimension, a (Å), and the agreement factors after Rietveld
(0.0 ≤ x ≤ 0.75) composite oxides
refinement of the unit cell structure of A1-A4 of Bi2+xAlxNi4-3xO7+δ
0.75) composite oxides.
(0.0 ≤x≤
Table 4.4.2 Selected Bond lengths and bond angles of Bi2+xAlxNi4-3xO7+δ
system
(0.0 ≤ x ≤ 0.75)
Table 4.4.3 Generated positions of atoms in the asymmetric unit of Bi2+xAlxNi4-3xO7+δ
(0.0 ≤ x ≤ 0.75) system
Table 4.7 Observed concentration of Ni2+ ions and observed EPR giso
300 K, 77 K and 6 K of Bi
-values of A1-A4 at
Table 4.8 Observed magnetization (Ms), coercivity (Hci), retentivity (Mr
the hysteresis loop, magnetic susceptibility(χ), Weiss constant(θ) and
), total area of
exchange integral (j) of A1-A4 of Bi2+xAlxNi4-3xO7+δ
Table 4.9. Direct band gap values of A1-A4 calculated using absorption coefficient.
(0.0 ≤ x ≤ 0.75) system.
Table 5.1 Unit cell parameters, calculated and observed densities and average crystallite
sizes in B1-B4 of Bi2+xCexNi4-3xO7+δ
Table 5.2 Generated Cartesian coordinates (xyz) before and after refinement of the
(0.25 ≤ x ≤ 1.0) composite oxides
atomic positions in the asymmetric unit in B1-B4.
Table 5.3 (a) Selected bond length of B1
x
Table 5.7. Observed magnetization (Ms), coercivity (Hci), retentivity (Mr
the hysteresis and magnetic susceptibility, of Bi
), total area of
2+xCexNi4-3xO7+δ
Table 5.8 Band gap energy values of B1-B4 respectively
Table 6.1 Unit cell parameters, calculated and observed densities and average crystallite
sizes in C1-C4 of Bi2+xYbxPd4-3xO7+δ
Table 6.4.1 Generated positions of atoms in the asymmetric unit
(0.25 ≤ x ≤ 1.0) composite oxides
Table 6.4.2 Bond angles between the atoms
Table 6.4.3 (a) Bond length of C1
Table 6.4.3 (b) Bond length of C2
Table 6.4.3 (c) Bond length of C3
Table 6.4.3(d) Bond length of C4
Table 6.6 Observed g – values in C1-C4
Table 6.7 Observed magnetization (Ms), coercivity (Hci), retentivity (Mr
the hysteresis and magnetic susceptibility, of Bi
), total area of
2+xYbxPd4-3xO7+δ
Table 6.8. Direct band gap energy values of C1-C4
Table 7.1 Unit cell parameters, calculated and observed densities and average crystallite
sizes in D1-D4 of Bi2+xGaxPd4-3xO7+δ
Table 7.4.1 Generated positions of atoms in the asymmetric unit
(0.15 ≤ x ≤ 0.60) composite oxides
Table 7.4.2 Reliability factors
xi
), total area of
(0.15 ≤ x ≤ 0.60) system
SYNOPSIS
The systematic studies and correlating the properties with the structures of solid
materials has been the subject of intense investigations due to their application
potentialities in many areas. The transition metal nanocomposite oxides which normally
are relatively easy to prepare with low cost by sol-gel method as well as the interesting
diverse physical properties have attracted much attention as the new materials in recent
years. Tailoring specific properties of solids such as magnetic, optical, electronic etc. is
important to utilize the solid as a material. However, it is necessary to ensure if the
material is monophasic and to what extent for such applications.
Currently the increasing interest in designing and preparing rare-earth - transition
metal oxides have also received extensive attention due to their unique 3d-4f orbital
interactions and fascinating chemical and physical properties such as electronic energy
band structures and magnetic ordering that results from two different types of orbitals
with distinct energy levels (3d of transition metal and 4f of rare-earth ions). In these
materials the 4f electrons of the rare earth ions polarize their 5d bands, which give the 5d-
3d short range interaction with the transition metal. The 5d band polarizations are
oriented parallel to 4f moments because the local 4f-5d exchange interactions are
positive.
xii
The study of physical properties of such materials requires single-phase samples
as the electronic behaviour and magnetic properties are closely related to the structure.
Therefore, it is necessary to establish whether the samples are indeed monophasic and to
what extent. The sol-gel method, a versatile and relatively low-cost technique makes it
possible the prepare varieties of solid materials, crystalline as well as amorphous, whose
structure and other properties differ significantly from that of solid materials prepared by
other traditional solid state techniques.
In this thesis, series of monophasic nanocomposite oxides in the series of
Bi2+xAxD4-3xO7+δ
Chapter - 1:
(A=Al, Ce, Yb & Ga; D=Ni & Pd) are synthesized by sol-gel method
via nitrate-citrate route and their magnetic, optical and electronic properties are studied
by a varieties of direct structure-sensitive techniques.
This chapter comprises an adequately thorough literature survey on
nanocomposite metal oxides with special emphasis on transition metal and rare-earth
mixed oxides and their chemical and physical properties such as crystal structures,
structural morphology and stability, and potential applications as magnetic, optical and
electronic materials with relevant references. A short introduction to the applications of
nanostructured metal oxides is also included. Importance of transition metal-rare-earth
metal based single phase materials has been discussed at length in this chapter. The main
objectives and the scope of the present investigation are also outlined as clearly as
possible.
xiii
In this chapter, the experimental procedures and the techniques employed in this
investigation are descried with necessary theoretical background.
Chapter – 3:
Chapter - 3 describes the complete synthesis of the samples using sol-gel method
via nitrate-citrate precursor route and characterization techniques of the samples studied
are described. In addition to the preparation procedures, the characterization techniques
include powder x-ray diffraction (XRD), differential scanning calorimetry (DSC),
differential thermal analysis (DTA), thermogravimetry (TG), scanning electron
microscopy (SEM), energy dispersive analysis of x-rays (EDX), magnetic measurements
by vibrating sample magnetometer (VSM), infra-red (IR) spectroscopy, electron
magnetic resonance (EMR) spectroscopy in the range 5-300 K, optical absorption studies,
chemical analysis, density measurements and calculations of electronic properties such as
energy band structures, density of states (DOS) and related optical properties using
CASTEP (Cambridge Serial Total Energy Package) programme package which uses the
plane-wave density functional theory (DFT).
Chapter - 4:
Chapter - 4 describes the results and discussion of Bi2+xAlxNi4-3xO7+δ (A1-A4: x
= 0.0, 0.25, 0.50, 0.75) (system-A) nanocomposite oxides. Analysis of the powder XRD
patterns by Fullprof shows cubic unit cell with lattice parameters in A1-A4: a = 10.2678,
10.1197, 10.1183, 10.1134 Å and space group Pm3n. From the comparison of the
observed (A1-A4: 4.398, 4.946, 5.169, 4.825 g/cm3) and calculated (A1-A4: 4.680,
4.999, 5.097, 4.520 g/cm3) densities, the Z value is determined to be 4. The average
crystallite sizes in A1-A4 determined by Scherrer’s relation are found to be in the range ~
xiv
42-61 nm. The DTA-TG results show no phase transitions in the range…