Modern technology systems, such as computing machines, high-performance engines and atomic reactors, require new and better stuffs than have antecedently been available. Improved stuffs and procedures will play an of all time increasing function in attempts to better energy efficiency, promote environmental protection, develop an information substructure and supply modern and dependable transit and civil substructure systems. The natural resources from which these and other stuffs are created are less available today than in the past, making a demand for research concerned with the choice and design of stuffs. In certain industries, the demand for energy-efficiency, energy transition systems and stuffs with the ability to defy hostile chemical and/or thermic environments has sparked a turning involvement in processing and belongingss of ceramic stuffs. In add-on, the go oning tendency towards miniaturisation in the electronics industry imposes invariably turning demand on semiconducting material belongingss and requires the development of new and advanced processing techniques.
While ceramics have traditionally been admired for their mechanical and thermic stableness, their alone electrical, optical and magnetic belongingss have become of increasing importance in many cardinal engineerings including communications, energy transition and storage, electronics and mechanization. Such stuffs are now classified under Electroceramics as distinguished from other functional ceramics such as advanced structural ceramics. Historically, developments in the assorted subclasses of Electroceramics have paralleled the growing of new engineerings. Progresss in stuffs research, hence, enable advancement across a wide scope of scientific subjects and technological countries, with dramatic impact on society.
The extended research devoted to the stuffs of solids during the last three decennaries has led to great progresss in the apprehension of the belongingss of solids in general. Recently one country of really active research has been in the assorted oxide ceramic systems. These have been of peculiar involvement because of their easiness of fiction, flexibleness and the fact that a broad scope of belongingss can be obtained by permutation of one ion for another. One of the most extensively studied groups of compounds is the O octahedral type ferroelectrics.
The word Nanotechnology merely nano in its signifier, means a billionth ( 1 x 10-9 ) of a metre length of measuring. It is the survey of control of affair at atomic and molecular graduated table degree and it deals with constructions of the size100nm and/or below. Reflecting many of the nanoscience possibilities, Richard P. Feynman emphasized in his talk on “ There is Plenty of Room at the Bottom ” in the twelvemonth 1959. In his talk, Feynman thought that, what might be on the molecular graduated table, and challenged the people of engineering “ to happen ways of manipulating and commanding things on a little graduated table ” . Inspired by the visual image of Feynman, today, nanoscience is defined as the survey of stuff use and control at the molecular graduated table, that is, a spacial graduated table of the order of a few hundred As, less than one-thousandth of the breadth of a human hair.
Now, in the present yearss, nanotechnology is used in about all Fieldss such as medical specialty, electronics, energy production etc, runing from fresh extensions of conventional device natural philosophies, to complex new designs based on molecular self-assembly, to developing new stuffs and devices etc on nanoscale measuring.
Nanoscale stuffs are those stuffs which fall in between atoms / molecules and condensed affair. These stuffs have one or more dimensions in the scope of 1 to 100 nanometres. The size of a nanoparticle normally is less than 100 nanometer. The ground that size affairs is that the belongingss of stuffs can hold some unexpected differences from their behaviour in larger majority signifiers that makes for new application chances. The two grounds for this alteration in behaviour are an increased comparative surface country ( bring forthing increased chemical responsiveness ) and the increasing laterality of quantum effects. The physicochemical belongingss of nanomaterials depend on their size, form, composing, etc. The interesting belongingss that alteration with size and form are chemical responsiveness, runing point, optical and magnetic belongingss, specific heat, etc [ 1 ] .
Incremental nanomaterials are stuffs that have improved belongingss at the nanoscale, typically as a consequence of their greatly increased surface country, but do non typically take advantage of the quantum effects. Nanoparticles are already seeing application, taking advantage chiefly of the high surface country of these all right pulverizations. Nanoceramic pulverizations, the most commercially of import of which are simple metal oxides, constitute about 90 % of the entire market. For illustration, nano-sized Zn oxide atoms are in usage in sunblock.
Evolutionary nanotechnology takes advantage of the alterations that can happen in stuffs at the nanoscale related both to increased chemical responsiveness and the increasing importance of quantum effects. Examples include nanoscale detectors that exploit the big country of nanotubes and semiconducting material nanostructures such as quantum points and quantum Wellss.
1.2.2 Basic Structures of Nanomaterials
Nanoparticles – ultrafine solid atoms on a nanoscale including nanopowders and nanocrystals ;
Nanotubes – hallow nanoscale atoms including nanotubes, nanohorns and nanocapsules ;
Nanostructured stuffs and coatings – stuffs made of structural elements ( bunchs, crystals, molecules ) with dimensions in the nano-range and which may organize movies or be free standing ; and
Nanocomposites – mixtures of constituents at least one of which has nanoscale dimensions.
1.2.3 Applications of Nanomaterials
Clay nanoparticles in packaging stuffs, where reduced porousness leads to less gas entrance ( e.g. less gas such as O that spoils nutrients ) ;
Rolled black lead nanotubes used in coatings on auto bumpers that better keep their form in a clang ;
Carbon nanotubes which are beginnings of filed-emitted negatrons and create enhanced phosphorescence e.g. in “ jumbotron ” lamps used at many athletic bowls ;
Nanoparticles of Zn oxide in sunblocks, more efficient at absorbing UV than more traditional white Ti dioxide lotions and go forthing the lotion smooth and transparent ;
Fabrics which are soil and fold immune due to naocoatings ;
Nanoparticles used as antiseptics, for abradants and in pigments ;
Nanocoatings for spectacle spectacless ( doing them scratchproof and cleft resistant ) ;
Nanocoatings for tiles to cut down slipping ;
Electrochromic of self-cleaing nanofilm coatings on Windowss, which in sunlight interruptions down soil and helps the H2O falling on it to transport the soil off ;
Nanofilms with non-stick belongingss used as anti-graffiti coatings for walls ;
Ceramic coatings for solar cells to better abrasion and eroding oppositions ;
Nanoceramics for more lasting and better medical prosthetics.
Nanoparticles research is presently an country of intense scientific research, due to a broad assortment of possible applications in biomedical, optical, and electronic Fieldss. Processing, belongingss and cost issues are forcing down the atom sizes of pulverizations used in a assortment of industries. Fine, ultrafine and nanostructured pulverizations are now critical to advancement of legion applications.
1.3 PEROVSKITE FERROELECTRICS
Many oxide constructions are based on close wadding of cations and anions. A slightly different construction occurs where big cations are present, which can organize a close jammed construction along with the O ions. Calcium titanate ( CaTiO3 ) was the first compound to be classified as a perovskite, by Russian geologist Perovsky. The most normally studied ferroelectrics have the three-dimensional perovskite construction ( in paraelectric stage ) with chemical expression ABO3. As handily drawn ( Fig. 1.1 ) , A- site cations occupy the corners of a regular hexahedron, while B-site cations sit on the organic structure centre. Three O atoms per unit cell remainder on the faces. The lattice invariable of these perovskite is ever near to 4a ( where ‘a ‘ is the lattice invariable ) due to the rigidness of the O octahedral web and the chiseled O ionic radii of 1.35 A .
The A- and B-site cations are 12- and 6-coordinated severally, and the A-site cation is usually larger than the B-site cation. The O anion has a coordination figure of 6. Assuming that all the ions are difficult domains, the lattice parametric quantity a of the three-dimensional perovskite is given by
( 1.2 ) or
( 1.3 )
as shown in Fig. 1.2 ( a ) and ( B ) . Here, , and are the ionic radii of the 12-coordinated A-site cation, 6-coordinated B-site cation, and 6-coordinated O anion, severally. The stableness of the perovskite construction besides can be described geometrically as the ratio of Eq. ( 1.2 ) to Eq. ( 1.3 ) , defined as the tolerance factor ‘t ‘ by
( 1.4 )
It is advantageous that the A- and B-site cations are in contact with O anions for an ABO3 compound to organize a stable perovskite construction. That is, the perovskite construction is more stable if t i‚» 1.0.
A practical advantage of the perovskite construction is that many different cations can be substituted on both A and B site without drastically altering the overall construction. Complete solid solution is easy formed between many cations, frequently across the full scope of composing. Simple solid solution series are fundamentally of two types: substitutional solid solutions and interstitial solid solutions. In substitutional solid solutions the atom or ion that is being introduced straight replaces an atom or ion of the same charge in the parent construction while in instance of interstitial solid solutions the introduced species occupies a site that is usually empty in the crystal construction. Even though two cations are compatible in solution, their behaviour can radically be different when apart from each other. Thus it is possible to change the belongingss of the stuffs such as Curie temperature, piezoelectric coefficient etc. with a little permutation of given cation.
Figure: 1.1 Cubic ABO3 Perovskite Structure and Geometrical Consideration for Lattice Parameter ‘a ‘
CARBON NANOTUBES ( CNTs )
In the twelvemonth 1991 Iijima [ 2 ] , discovered Carbon Nanotubes ( CNTs ) by chance during his experiment on synthesis of fullerenes by arc-discharge method. Subsequently the CNTs have been drawn most scientists and research bookmans into great involvement, both from cardinal position point and for future applications. He invented foremost the Multiwalled Carbon Nanotubes ( MWCNTs ) [ 3 ] and so derives from there the Single Walled C Nanotubes ( SWCNTs ) . The MWCNTs consist of 2 to 30 homocentric graphitic beds, diameter of which range from 10 to 50nm and length of more than 10Aµm. on the other manus, SWCNTs have much dilutant from 0.34 to 1.4nm. The most noticeable characteristics of these constructions are their mechanical, electronic, electrical, chemical and optical features, which open a agency to future applications. On individual wall nanotubes, these belongingss can besides be measured. For commercial application, big measures of purified nanotubes are needed. Furthermore, these constructions are atomically specific significance that each C atom is still treble coordinated without any swinging bonds. CNTs have been used to construct prototype nanodevices in many research labs. These nanodevices consist of field-effect transistors, metallic wires, electromechanical detectors and shows. They prospectively form the footing of future all-carbon electronics.
An ideal nanotube can be consideration of as a hexangular web of atoms of the C, which has been rolled up to construct a seamless cylinder. Just a nanometre across, the cylinder can be 10s of micrometers long, and each terminal is “ capped ” with half of a fullerene molecule. Single-wall nanotubes can be consideration of as the cardinal cylindrical construction, and these organize the edifice blocks of both multi-wall nanotubes and the ordered arrays of single-wall nanotubes called ropes. Many theoretical surveies have predicted the belongingss of single-wall nanotubes. Primary synthesis methods to fix nanotubes include methods of optical maser extirpation, arc discharge, gas stage catalytic growing from C and C beginnings and chemical vapor deposition. Sing the application of C nanotubes as supports in complexs which requires production of big sum of C nanotubes economically, gas stage techniques like chemical vapour deposition ( CVD ) tenders the greatest potency for optimisation of nanotube production.
MOTIVATION ( Seeking for new stuffs )
For all the astonishing progresss that have been made in semiconducting material engineering, most significantly in miniaturisation and processor velocity, some ends remain elusive. Among these ends is recognizing the “ ideal ” nonvolatilizable memory – memory that retain information even when the power goes. As modern portable electronic devices such as nomadic phones and note book computing machines become more and more popular, there is a confirmed addition in the demand for non-volatile memories. Semiconductor memories such as dynamic random entree memories ( DRAMs ) and inactive random entree memories ( SRAMs ) presently dominate the market. However, the chief job with these memories is that they are volatile.
Since the first find of ferroelectricity in Rochelle salt many other stuffs with crystal constructions of perovskite, pyrochlore and tungsten bronze have been found and studied for the applications in memory devices. Ferroelectric Random Access Memories ( FeRAM ) are most promising options, which are non-volatile and have the added benefits of greater radiation hardness and higher velocity.
These devices use the switchable self-generated polarisation originating due to the positional bistability of constitutional ions and thereby hive awaying the information in the signifier of charge. Since the response clip of the ion supplanting is of the order of nano 2nd or less, non-volatile random entree memory can be realized utilizing ferroelectric capacitances in which two binary provinces of “ 0 ” and “ 1 ” are represented by the way of self-generated polarisation. Their non-volatility is because the polarisation remains in the same province after the electromotive force is removed, and their radiation hardness allows devices incorporating these memories to be used in rough environments, such as outer infinite. One of the jobs with ferroelectric memories is their inclination to free informations after a certain figure of read/write rhythms. This phenomenon is called weariness. At the minute the weariness opposition of FRAMs is non sufficient for them to replace wholly semiconducting material memories, but this can be improved with farther optimisation of both composing and microstructure.
Organization of the thesis
To obtain high quality stuffs ( such as ferroelectrics, CNTs etc ) for a specific usage, it is necessary to understand assorted phenomena refering structural and electrical belongingss of the stuffs. For this intent it is desired to do available as many experimental informations as possible by utilizing assorted techniques. Hence the purpose of the research described in this thesis is focused on the synthesis and word pictures of BiFeO3, xCrFe2O4- ( 1-x ) BiFeO3 nanoceramics and Carbon Nanotubes ( CNTs ) . The consequence of various-dopant-induced alterations in structural, dielectric, ac electric resistance, ferroelectric hysteresis, mechanism of the dielectric extremum widening and frequence scattering have been addressed. The basic thought is to develop a low processing temperature and heighten the insulator and ferroelectric belongingss of these ceramics.
The followers are the chief aims of the present work.
To analyze the processing conditions and synthesise pure/doped, homogenous and reactive BiFeO3, xCrFe2O4- ( 1-x ) BiFeO3 nanoceramics and Carbon Nanotubes at a low processing temperature based on the apprehension of their transmutation dynamicss.
To look into the decomposition and stage formation behaviour of the stuff by TGA, DTA, FTIR and XRD for better apprehension of the structural stage passage.
To analyze the electrical and morphological features of the synthesized stuffs in order to understand the cardinal scientific discipline, this will take to farther apprehension of the nexus between microstructure and ferroelectric belongingss.
To analyze the mechanical belongingss such as bending, buckling and tortuosity effects under different conditions for Single and Multi walled Carbon Nanotubes utilizing Finite Element Analysis simulation technique.
The brief description and the contents of this thesis ( chapter-wise ) are given below:
Chapter-1 describes the brief debut of the ferroelectrics and cardinal facets of ferroelectricity with a specific reference of Bi ferrite oxide ( BFO: a Perovskite ferroelectric ) ; Cr ferrite oxide ( CrFe2O4 ) belonging to the aurivillius household of Perovskite ferroelectrics, their construction and importance and Carbon Nanotubes ( CNTs ) . In Chapter-2 a brief literature study has been presented related to bismuth ferrite oxide ( BFO ) , chromium ferrite oxide ( CFO ) perovskite constructions, and Carbon Nanotubes. In order to acquire better apprehension of structure-property dealingss of solids, assorted experimental techniques are usually used. Hence the basic rules and working of assorted instruments used in the present work are given in Chapter-3.
Chapter-4 discusses Polycrystalline samples of BiFeO3 were synthesized at low temperature utilizing sol-gel technique and studied the features under XRD, SEM, DTA analysis etc. A portion of this chapter has been published as a research paper entitled “ Effect of Sintering Temperature on Structural and Electrical Properties of BiFeO3 Multiferroic Nanoceramics ” in Indian Journal of Engineering Materials and scientific disciplines – , 2010
Chapter-5 nowadayss experimental survey on synthesis and word pictures of xCrFe2 O4- ( 1-x ) BiFeO3 Multiferroic Nanocomposites, with x = 0.0, 0.1, 0.2, 0.3 and 0.4. A portion of this chapter has been published as a research paper entitled “ Structural, Magnetic and Dielectric Properties of xCrFe2 O4- ( 1-x ) BiFeO3 Multiferroic Nanocomposites ” in Journal of Physica B – Condensed Matter, 405, 2010, pp 1325-1331.
Chapter-6 contains a elaborate survey of synthesis and word pictures of Carbon Nanotubes ( CNTs ) . All the experimental consequences are supported on theoretical footing from literature. A portion of this chapter has been published in the signifier of a research paper entitled “ Synthesis and Characterization of Carbon Nanotubes ” in International Journal of Technology Spectrum – JNTU-H, ( accepted, 2009 ) . Chapter 7 nowadayss successful mold and analysis of Single Walled Carbon Nanotubes ( SWCNTs ) and studied bending and clasping distortions under inactive and dynamic loading conditions. A portion of this chapter has been published in the signifier of a research paper entitled “ Simulation Studies on Dynamic response of individual walled C Nanotubes under flexing – clasping tonss in FEA Approach ” in the International Journal of Nanotechnology and Applications – Vol: 2, No.3, ( 2009 ) , , pp.49-60 published by Research India Publications – New Delhi.
In Chapter 8, trades with simulation surveies on multiwalled C nanotubes utilizing Finite Element Analysis. For analysis intent, 13, 14 and 15 walled tubings are considered for bending, buckling and torsional tonss. The consequences were compared with old work in the literature. Finally, Chapter 9 gives the decisions and recommendations for future research. At the terminal of this thesis transcripts of the published research documents are enclosed.