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Crystal Engineering Studies with Azole based Ligand Molecules
Full text linkCrystal engineering or the understanding of intermolecular interactions in the
context of designing new solids with desired physical and chemical properties is concerned
with the systematic architecture of crystal structures. The two main strategies currently in use
for crystal engineering are based on hydrogen bonding and coordination complexation. These
may be understood with key concepts such as the supramolecular synthon and the secondary
building unit (SBU). Coordination polymers or metal-organic frameworks usually involve
strong covalent bonds, whereas weak hydrogen bonds and other non covalent interactions are
instrumental for networks incorporating only organic molecules. There are also various
factors which play crucial role in dictating the final topology of the network, for example the
counter anion present in the system, solvents used, etc. For hydrogen bonded networks,
identification of supramolecular synthon that results from definite molecular recognition
processes draws prime attention. In this context the present thesis work can be divided into
two parts: the first part deals with coordination polymers and the next part is based on
supramolecular architectures. The pyrazole based molecule, methylene bis(3,5-
dimethylpyrazole) (H2MDP), is chosen as a major constituent of the networks to explore
different aspects of crystal engineering studies involving metal organic frameworks as well as supramolecular networks.Submitted to the University of Calcutta in 2014 for degree of Doctor of Philosophy (Sc.)Under DST project grant and research was conducted in Inorganic Chemistry division under Dr. Raju Mondal at IAC
Synthetic Studies on the Catalysis by Supported Metal, Metal Nanoparticles and Other Benign Materials
Full text linkThe main object of this present work is to develop useful synthetic
procedures using transition metal based catalysts and Photocatalysts in an
environmentally benign way. The thesis has been divided into four chapters.
Chapter-1 deals with “Heterogeneous Catalysis’’. In chapter-I, section-I, a
brief review on heterogeneous Cu catalyst has been described. Section II
consists of Heterogeneous Cu-Al2O3 catalyzed solvent controlled N-arylations
of cyclic amides and amines with bromoiodoarenes. Chapter-2 consists of two
sections where section-I explains the catalytic activity of Cu nanoparticles in
various organic reactions. In section-II magnetically separable CuFe2O4
nanoparticle catalyzed S-vinylations and S-arylations have been demonstrated.
Chapter-3 of the thesis is based on “Catalysis by Homogeneous Metal
Complexes” and has been split into two sections. Section-I includes a brief
review on the homogeneous Ni catalysts and their applications in organic
synthesis. Section-II describes Ni-Cu co-catalyzed cross coupling of styrenyl
and vinyl halides with phenols for the synthesis of aryl-vinyl ethers. Chapter-4
of the thesis deals with “Sustainable synthesis of organoselenides and
tellurides’’. In chapter-4, section-I, a brief review on the synthesis of
organoselenides has been described. Section-II contains Zn mediated synthesis
of diaryl chalcogenides from aryl diazonium tetrafluoroborates. Section III
includes a brief review on recent developments of photoredox catalysis in
organic synthesis and after that a direct synthesis of aryl and heteroaryl
amines to selenides has been discussedResearch was conducted under supervision of Prof. B C Ranu, Organic Chemistry division under SCS [School of Chemical Sciences]Research was conducted under CSIR fellowship & DST research gran
Some Studies on the Prospect of Finding New Physics Beyond the Standard Model at the LHC
Full text linkAfter the discovery of a ∼ 125 GeV Higgs boson at the Large Hadron Collider (LHC),
now the Standard Model (SM) of particle physics is complete although there are still
some doubts over the fact that this can be a beyond the Standard Model (BSM) Higgs
boson. More updated data on Higgs boson coupling measurements will reveal its true
identity. Meanwhile, we need to go beyond the SM to address some vital experimental
findings. One of them is the neutrino oscillation data that indicates at least two
neutrinos have tiny but non-zero masses. The other one is the existence of Dark
Matter (DM) revealed from cosmological data. Weak scale supersymmetry (SUSY)
is the most popular choice for explaining these new physics phenomena beyond the
SM. However, even Minimal Supersymmetric Standard Model (MSSM) itself is not
sufficient to explain the neutrino oscillation data under R-parity conserving scenario.
In this thesis, we, therefore, attempt to explore a SUSY model with added singlets
that can account for small neutrino masses by means of inverse seesaw mechanism. As
a consequence, we can have a mixed sneutrino lightest SUSY particle (LSP) that may
be as light as ∼ 50 GeV. Within R-parity conserving scenario, this LSP can serve as
a very good DM candidate satisfying all existing constraints arising from collider, DM
and low energy experiments. This model can have enhanced same-sign dilepton final
states with large missing energy coming from gluino and squark pair as well as squarkgluino
associated productions and their cascade decays through charginos. The two
body decays of the lighter chargino into a charged lepton and a singlet sneutrino has
a characteristic decay pattern which is correlated with the observed large atmospheric
neutrino mixing angle. This feature can be probed at the LHC through trilepton
channel. Moreover, the ∼ 125 GeV Higgs boson now have a new decay channel into
a pair of LSP sneutrinos that is completely invisible. Most recent data published by
ATLAS and CMS collaborations at the LHC in different Higgs boson decay channels
constrain this sort of non-standard decays. We perform a two parameter global analysis
of the available experimental data to date to determine the optimal invisible Higgs
boson branching fraction in this scenario. This new decay provides us a new missing
energy channel that can be probed at the LHC. We present detailed cut-based analyses for these different proposed signals at the LHC to test the viability of such a scenario.Research conducted under supervision of Prof. Sourav Roy, Theoretical Physics division under SPS [School of Physical Sciences]Research conducted under DST research gran
Functionalized Graphene-Polymer Systems: Properties and Applications
Full text linkThe present thesis entitled “Functionalized Graphene-Polymer Systems: Properties and
Applications” deals with the preparation, characterization and applications of graphene oxide polymer hybrid systems as well as functionalized graphene. Chapter-1 deals with a brief history about the rising star graphene oxide, evaluation of its
synthetic approaches, structural aspects of graphene oxide, preliminary idea about chemical
reactivity of graphene oxide, functionalization of graphene oxide by means of both covalent
and non-covalent approaches, fluorescence property of graphene oxide and its functionalized
derivative. A literature review on various plausible applications of fluorescent graphene oxide
and functionalized graphene oxide in diverse fields are also summarized here. At last, aims
and objectives of the present thesis are depicted in a nut shell.
Chapter-2 includes the experimental section of the thesis and the different types of characterization
techniques are also briefly described here.
Chapter-3 illustrates the preparation of fluorescent graphene oxide-methyl cellulose (GOMC)
hybrid at low pH and the application of this fluorescent material is described.
Chapter-4 accounts the preparation of another fluorescent graphene oxide-polymer hybrid
which utilizes poly(vinyl alcohol) [PVA] as a bio-compatible polymer. The highly
fluorescent material reported here, provides a nice platform to selectively detect toxic Au3+
ions.
Chapter-5 deals with the synthesis of sulfonated graphene (SG), a more water dispersible
graphene derivative. The fluorescence property of SG at different pH (pH 4, 7 & 9.2) has
been studied. Based on the strong overlap between emission spectrum of SG and absorption
spectrum of riboflavin (RF, vitamin B2) at pH 4, SG has tactfully been used as donor for the
fluorescence resonance energy transfer (FRET) process to detect vitamin B2 in presence of
other biomolecules.
Chapter-6 demonstrates the covalent functionalization of GO using a bio-compatible
polymer, Poly(N-isopropylacrylamide) [PNIPAM] via free radical polymerization. The
synthesized material exhibits aqueous stability, bio-compatibility as well as fluorescence property at neutral pH. The synthesized nanomaterial is employed as a successful nanocarrier for the delivery of both hydrophilic and hydrophobic drugsThe research was conducted under the supervision of Prof. A K Nandi of the Polymer Science Unit under [SCS] School of Chemical SciencesThe research was conducted under CSIR project and fellowshi
Study of Niosomes, Proteins and Live Cell using Fluorescence Correlation Spectroscopy and Microscopy
Full text linkIn this thesis, we have focused our attention on three different process, - diffusion of organic dyes, conformation dynamics of protein and solvation dynamics. Diffusion of organic dyes provides important information on the micro-viscosity and heterogeneity of the system. We have determined the diffusion coefficient and heterogeneity inside a niosome using fluorescence correlation spectroscopy. We also determined the micro-viscosity of different region of a live cell by measuring the diffusion coefficient of dyes in those regions. We studied the effect of solvent mixtures, such as binary mixtures of water and
di-methyl sulfoxide (DMSO) and water and ionic liquid, on the structure and
conformational dynamics of an enzyme, lysozyme. Finally, using time resolved confocal microscopy, we have studied solvation dynamics in different regions of a biological cell - nucleus, cytoplasm, lipid droplets and cell membrane.Research was conducted under the supervision of Prof. Kankan Bhattcharyya of the Physical Chemistry division under SCS [School of Chemical Sciences]Research was carried out under DST research grant and CSIR fellowshi
SYNTHESIS OF NANOHYBRIDS, NANODOTS AND CORE-SHELL NANOMATERIALS AND THEIR APPLICATIONS
Full text linkThe research embodied in the present thesis entitled “SYNTHESIS OF
NANOHYBRIDS, NANODOTS AND CORE-SHELL NANOMATERIALS AND THEIR
APPLICATIONS” deals with the synthesis and characterization of core-shell
nanoparticles and various nanohybrid systems and their various applications.Chapter 1 is the general introduction and it provides the comprehensive
literature survey on nanomaterials including metal nanoparticles/nanoclusters, coreshell
nanoparticles, nanohybrid gels with carbon-based nanomaterials and noble metal
nanoparticles/nanoclusters. This chapter highlights structural and morphological
features of nanohybrid gels and their different applications. This chapter also consists of
different classes of carbon-based nanohybrid gels, their synthetic procedure and various
applications.
Chapter 2 describes the reagents used and experimental procedures, carried out
to perform the entire work embodied in this thesis.
Chapter 3 describes the synthesis of Ag@Au core-shell nanoparticles by using a
fluorescent dipeptide β-Ala-Trp in water medium and at a room temperature without
using any external reducing and stabilising agents. The shell thickness of Au can also
vary from 1:1 to 1:2 by changing the Au (III) precursor keeping the other conditions
same. The optical property of the core-shell nanoparticles varies with the shell
thickness. Interestingly, these core-shell nanoparticles exhibit good catalytic activity for
the reduction of nitrophenols to aminophenols and nitroanilines to aminoanilines. A
series of nitrophenol and nitroaniline compounds have been taken as substrates for
reduction. Moreover, this core–shell nanoparticle displays remarkable difference in
catalytic property for reduction of nitro group with variation of shell thickness. This catalyst (Ag@Au core-shell nanoparticle) can also be recycled for several times
indicating its reusability.Chapter 4 describes the synthesis of graphene oxide (GO)-based hydrogels by
using vitamin B2/B12 and vitamin C (ascorbic acid) in water (at neutral pH value). These
gel-based soft materials have been used to synthesize various metal nanoparticles,
including Au, Ag, and Pd nanoparticles, as well as nanoparticle-containing reduced
graphene oxide (RGO)-based nanohybrid systems. This result indicates that GO-based
gels can be used as versatile reactors for the synthesis of different nanomaterials and
hybrid systems on the nanoscale. Moreover, the RGO-based nanohybrid hydrogel with
Pd nanoparticles was used as an efficient catalyst for C-C bond-formation reactions with
good yields and showed high recyclability in Suzuki–Miyaura coupling reactions.
Chapter 5 provides a vivid description the preparation of trihybrid gel by
incorporating graphene oxide (GO) and in situ synthesized gold nanoparticles (AuNPs)
into the pyrene conjugated single amino acid-based native gel matrix. The morphology
of this system indicates the presence of three distinctly different nanostructures:
nanofibers, nanosheets, and nanoparticles. Rheological studies reveal that stiffness of
the gel increases with the inclusion of GO into the native gel and stiffness of this hybrid
gel is increased further due to the incorporation of gold nanoparticles into the GO
containing hybrid hydrogel in a trihybrid system. Moreover, catalytic property of AuNPs
can be tuned from only AuNPs containing hybrid gel to trihybrid gel. The catalytic
efficiency of this trihybrid system is enhanced relative to that of AuNPs in a dihybrid
system.
Chapter 6 describes the in situ preparation of gel based various nanohybrid
systems by using sunlight. A naturally occurring amino acid L-phenylalanine derivative
has formed a hydrogel with graphene oxide (GO)/reduced graphene oxide (rGO) at
physiological pH and this hydrogel has been used in presence of silver ions and diffuse
sunlight to form initially a tri-nanohybrid system consisting of six atom silver
nanoclusters, nanosheets and nanofibers. Interestingly, a time-dependent morphological
transformation occurs in this nanohybrid system to form one tri-nanohybrid to another
tri-nanohybrid with the appearance of a novel, nanoscopic intermediate, tetrananohybrid
system consisting of four distinctly different nanomaterials (nanofibers,
nanosheets, nanosphere and nanoparticles). UV-Vis and fluorescence spectroscopic
analyses, transmission electron microscopic, X-ray photo electron spectroscopic and
MALDI-TOF mass spectral analyses with time have been applied to characterize these
morphological transformations in gel based nanohybrids. Interestingly, one of thesenanohybrid systems (silver nanoparticles containing rGO based hydrogel) show
catalytic property in reducing nitroarenes to aminoarenes and the catalytic efficiency is
modulated by changing the size of silver nanoparticles with time in diffuse sunlight. The
mechanism for different catalytic activities for different hybrids with varying size of
silver nanoparticles has also been deciphered.
Chapter 7 describes a new strategy of making peptide functionalized carbon
nanodots and these carbon nanodots were used as a template for making of ruthenium
nanodots from a ruthenium salt in the presence of a reducing agent, sodium
borohydride in water medium. These functionalized carbon nanodots exhibit a blue
emission with a high quantum yield (69.8%). Various techniques including UV-Vis,
fluorescence, FTIR, X-ray photo electronic (XPS), Raman and X-ray diffraction and
transmission electron microscopic (TEM) analyses have been used to characterize
carbon nanodots and hybrid nanodots. Moreover, this nanohybrid acts as a potential
catalyst for the reduction of organic azides to the corresponding amines in aqueous
medium with high yield, good chemoselectivity and remarkable reuability.
Each chapter (chapter 3 to 7) begins with a short ‘Introduction’ followed by
‘Experimental Section’, ‘Results and Discussion’ and ‘Conclusion’. For Convenience,Research was carried out under the supervision of Prof. A. Banerjee of the Biological Chemistry division under SBS [School of Biological Sciences]Research was conducted under CSIR fellowshi
Low Temperature Synthesis of Silicon and Carbon Nano-structured Thin Films and their Optimization for Optoelectronic Applications
No full textUsing low pressure planar inductively coupled RF plasma CVD at 87% H2-dilution to the SiH4 plasma, nc-Si:H films are prepared at low temperature that possess preferential growth along crystallographic orientation with I220/I111>1.2, bonded H-content of ~5.5 at%, a low microstructure factor ~0.56, along with a reasonably high σD ~5.2x10-4 S cm-1, ΔE~143 meV and σPh ~1.4x10-3 S cm-1. The growth of the nc-Si:H network has been optimized to a moderately high nanocrystallinity (~68%), with an average grain size ~8 nm. The overall network comprises with a significant fraction of ultra-nanocrystalline component, Xunc/Xnc ~0.47, which are dominantly inhabited by the thermodynamically preferred crystallographic orientation that provides expedient electrical transport perpendicular to the film surface and subsequently could facilitate photovoltaic accomplishment. The cross-sectional view of the fracture surface demonstrates columnar structures, closely correlated to the favored growth of the nanocrystallites along crystallographic orientation that retains direction perpendicular to the substrate surface. The underlying phenomena could be demonstrated as a consequence of preferential growth induced by high atomic H density present in the planar inductively couples SiH4 plasma obtained via much lower H2-dilution compared to that realized in conventional capacitively coupled plasma-CVD. The nc-Si:H films with precise material properties as well as the allied low-pressure ICP-CVD growth process could be of significant use in further progress of nc-Si solar cells. A comprehensive analysis on the evolution of the microstructure as well as the optical constants and dielectric functions of these intrinsic hydrogenated nano-crystalline silicon thin films has been performed by spectroscopic ellipsometry. The films are assumed to have a three-layer structure, with a thin incubation layer at the substrate/bulk interface, the bulk layer and a thin growth zone and surface roughness layer. Individual composition and the thickness of each layer have been estimated from the simulation of the ellipsometry data using Bruggeman effective medium approximation (BEMA). The ellipsometry results are correlated with atomic force microscopy and micro-Raman data of these films. The effect of the flow rate of SiH4 and the key role of hydrogen dilution on the growth dynamics, optical constants and dielectric functions of highly crystalline nano-Si films is discussed elaborately. The bulk crystalline volume fraction of the deposited films varies considerably (~67%–84%) with the change in flow rate of SiH4. With increasing SiH4 flow rate the overall bulk crystallinity reduces, however the ultra-nanocrystalline component (Xunc) enhances substantially that helps reducing the porosity and surface roughness. Further, aiming towards a specific application as antireflection coatings (ARC) in Si solar cells, the low temperature growth of DLC and HDLC films, by RF magnetron sputtering, has been optimized through comprehensive optical and structural studies.Various physical properties of the films e.g., (ID/IG) ratio in the Raman spectra, percentage of sp3 hybridization in XPS spectra, H-content in the network, etc, have been correlated with different ARC application properties e.g., transmittance, reflectance, optical band gap, refractive index, surface roughness, etc. The ARC properties have been optimized on unheated substrates, through systematic variations of RF power, gas flow rate, gas pressure and finally controlled introduction of hydrogen to the DLC network at its most favorable plasma parameters. The optimum HDLC films possess (T700)max ~95.8%, (R700)min ~3.87%, (n700)min ~1.62 along with simultaneous (Eg)max ~2.53 eV and ~73.2% of sp3 hybridization in the C-network, corresponding to a bonded H-content of ~23 at.%.Encouraging improvements of the ARC properties over the optimized DLC film were obtained with the controlled addition of hydrogen and the optimum HDLC films appear quite promising for applications in Si solar cells. Systematic materials development has been performed through comprehensive understanding of the parameter space and its optimization, as elaborately discussed. Furthermore, various process conditions are summarized that allocate different carbon nanostructures (spherical nano-diamonds, nano-plates, nano-rods, a-C wrinkles, etc.) grown by micro-wave plasma enhanced CVD (MW-PECVD) of CH4/H2 mixture. At an optimized MW power of 500 W, gas pressure of 30 Torr and at only 200 °C temperature, spherical shaped homogeneously distributed nano-structures of average size ~120 nm, embedded within a matrix made of fine-grain nanocrystallites were produced. The spherical structures were found to increase in number density with elevation of temperature. With pretreatment of the substrate by mechanical scratching nano-plate and nano-rod like structures could also be grown. Further, amorphous carbon wrinkles were formed by controlling the flow rate of the precursors. The bulk material was found to improve in crystallinity with the increment of pressure and highly polycrystalline nano-diamonds (1 1 1), along with graphitic [(1 0 0), (0 0 4)] inclusions, with an average size of 13 nm and number density ~8 × 108 cm−2 were grown at 70 Torr, at a low substrate temperature of 250 °C. The process conditions are further summarized and compared for two different chamber volumes, that allocate different phases of carbon grown at low temperature, by micro-wave plasma enhanced CVD (MW-PECVD) of CH4/H2 mixture. A higher chamber volume could be optimized to make spherical nano-diamonds, nano-plates, nano-rods, a-C wrinkles, etc. due to its molecular epitaxial deposition control, however in a very low growth rate. Whereas a lower chamber volume gives rise to highly controlled, less corrosive and confined plasma with relatively higher growth rate. As a result, even at a very high CH4 flow, at an optimized MW power of 500 W, gas pressure of 50 Torr, and unheated substrate, nano-diamond films with (111) crystallographic planes could be grown. In quest of further optimization, nano-diamond thin films have been successfully grown on unheated substrates using controlled secondary plasma, from (CH4+H2) gas mixture, generated within SS grid-like multiple mask assembly in MW-PECVD with reduced volume, optimized with variation of H2 flow. The quality of nano-diamonds improves systematically with reduced grain size and prominent presence of and crystalline diamond planes, on increasing H2-dilution. In view of basic understanding of the structure and the growth mechanism of various carbon nano-structures and the effect of plasma confinement and secondary plasma in MWCVD, a detailed study was performed using micro-Raman, FE-SEM, FEG-TEM, STEM, XPS. This study of variation and optimization of reactor volume and unique method of synthesis of nano-diamond using secondary plasma has never been reported earlier; this may open up a new field of study with enormous application possibilities, e.g., fabrication of field emission devices.Research was conducted under the supervision of Prof. Debajyoti Das of ERU under SPS [School of Physical Sciences]Research was carried out under IACS fellowship and gran
Functional Porous Nanocomposite: Synthesis and Application
Full text linkPorous nanomaterials have received great attention in different research field of nanoscience and
nanotechnology such as drug delivery, bioimaging, detection, catalysis, optics, energy and
environmental application. This is due to their high surface area, tunable pore size and structure,
chemical stability and versatile chemistry for functionalization. Most widely studied porous
materials are made of silica, carbon, titanium oxide and graphene. According to pore size the
porous materials are classified into three types. These are microporous materials of pore size less
than 2 nm, mesoporous materials of pore size 2 to 50 nm and macroporous materials of pore size
larger than 50 nm. Among these microporous materials have limited application due to small
pore size but other two porous materials have wide range of application.
Recent study shows that nanoparticle incorporated porous materials can be used for
multifunctional application. Various nanoparticles have their unique chemical and physical
properties. For examples, iron oxide nanoparticles (Fe3O4, Fe2O3) have magnetic property which
helps is the separation from solution. Semiconductor nanoparticles( QDs) have been used as
imaging probe due to their fluorescence property. Plasmonic nanoparticles(Au, Ag) are used for
the photodynamic therapy, dark field imaging and surface enhanced raman spectroscopy based
detection. TiO2, ZnO, CdS nanoparticles are used for photocatalytic degradation of various
pollutants. Nanoparticle incorporated porous materials have the property of nanoparticle as well
as the property of porous material. However, the synthesis of smaller size porous nanocomposite
is very important particularly for the targeting, drug delivery and imaging applications. In addition, appropriate functionalization of internal and external surface of the porous composite materials is important towards specific targeting, selective adsorption and specific catalysis. We have focussed our research in developing multifunctional porous nanocomposite with tunable particles size, good dispersibility and modification of surface with proper functional group for biomedical and water purification application.Research was conducted under the supervision of Prof. N R Jana of CAM under SPS [School of Physical Sciences]Research was carried out under CSIR fellowship and gran
Computational Study of Structures and Electronic Properties of Metal Clusters
Full text linkSubnanometer sized transition metal clusters have attracted a great deal of interest in recent years. In this thesis we have investigated the structures, electronic and optical properties, the structural evolution due to doping with a heteroatom, and the catalytic activity of subnanometer sized Aun (n = 2-20) clusters using various computational methods. Another major theme of this thesis has been to understand the mechanisms of organic reactions such as C–C coupling and cycloisomerization reactions triggered by transition metal complexes. We have reported electronic and chemical properties of novel 2D materials such as fluorographene, germanene, and germanane. One future extension of this work shall be the investigation of metal clusters anchored on these 2D systems for designing heterogeneous catalysts for vital organic transformations, which has been studied in the presence of naked metal clusters and metal complexes in the present thesis.Research was carried out under the supervision of Prof. Ayan Dutta of Spectroscopy division under SPS [School of Physical Sciences]Research was conducted under IACS fellowship and DST gran
First Principles Study of Electronic Structure and Magnetism in Functional Materials
No full textIn the present thesis work, we have employed rst principles calculations based on
density functional theory (DFT) to understand the electronic structure and magnetism
of several functional materials. We have studied the magnetic property of the
rare-earth based intermetallic compound Gd2In which is a rather unique system where
both localized 4f electrons as well as itinerant 5d electrons all originating from Gd are
responsible for its novel magnetic property with hardly any role of In s, p electrons. In
particular, analysing the response of Gd 4f and 5d moments in a magnetic eld using
xed spin moment method we have conclusively established the important role of Gd
5d electrons in the metamagnetic property of Gd2In. Next we have considered, local
cationic order and its impact on magnetism in the double perovskite LaSrVMoO6.
Experiments reveal unusual atomic scale chemical fluctuation in LaSrVMoO6 where
there are narrow patches of La-V and Sr-Mo rich phases. Our electronic structure
calculations reveal that the La-O covalency play a key role that leads to the preferential La, V and Sr, Mo ionic proximity and therefore the resulting patchy structure in LaSrVMoO6. In contrast to the suggestion that LaSrVMoO6 may be a half-metallic
antiferromagnet, our calculations on the experimentally realized patchy structure suggest that the system is metallic (not a half metal) and does not exhibit long range
magnetic order. Finally, we have studied the magnetic and phononic properties of
non-stoichiometric full Heusler alloys Ni2+xMn1 xIn and Ni2Mn1+xSn1 x. Our study
of the non-stoichiometric full Heusler alloy Ni2+xMn1 xIn reveal that these systems do not exhibit martensitic transition like the Ni2+xMn1 xGa alloys. The magnetic properties of the In samples however are very similar to the Ga counterpart. The
reduction of the total magnetic moment as a function of excess Ni concentration is
attributed to the progressive lling up of the Ni-d minority states with the availability of excess electrons upon Ni doping. The reduction in the ferromagnetic Curie temperature observed experimentally is argued to be due to the decrease in tion of the conduction (In s+p) electrons with excess Ni concentration leading to the
weakening of the RKKY like interactions. Finally, we have investigated the origin of
martensitic transition in Ni2Mn1:5Sn0:5 alloy. The phonon dispersion relation calculated
for Ni2Mn1:5Sn0:5 alloy with parallel alignment of the moment of the excess Mn
at the Sn site with the Mn already existing in the unit cell reveal softening of the TA2 mode analogous to Ni2MnGa and is responsible for the martensitic transition. Thorigin of the martensitic transition is traced back to the nesting of the Fermi surface in the minority spin channel.Research was conducted under the supervision of Prof. Indra Dasgupta of the Solid State Physics division under SPS [School of Physical Sciences]Research was carried out from DST grant and IACS fellowshi