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Top-down techniques take a bulk material, machine it, modify it into the

desired shape and product- classic example is manufacturing of integrated circuitsusing a sequence of steps sush as crystal growth, lithography, deposition,

etching, CMP, ion implantation

(Fundamentals of Microfabrication: The Science of

Miniaturization, Marc J. Madou, CRC Press, 2002)

Bottom-up techniques build something from basic materials

- assembling from the atoms/molecules up

- not completely proven in manufacturing yet

Examples:

Self-assembly

Sol-gel technology

Deposition (old but is used to obtain nanotubes, nanowires, nanoscale films)

Manipulators (AFM, STM,.)

3-D printers (http://web.mit.edu/tdp/www)

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Production of NanomaterialsThere are five widely known methods to produce nanomaterials,and they are as follows: Sol-gel synthesis, Inert gas condensation, Mechanical alloying or high-energy ball milling,

Plasma synthesis, and Electrodeposition.

A sol is a dispersion of the solid particles (~ 0.1-1 mm) in a liquidwhere only the Brownian motions suspend the particles.

A gel is a state where both liquid and solid are dispersed in eachother, which presents a solid network containing liquid components

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Sol-Gel SynthesisAll the above processes synthesize nanomaterials to varyingdegrees of commercially-viable quantities.To date, of all the above process, only sol-gel synthesis can Produce materials (both metals and ceramics) at

low temperatures Large quantities (to be commercially viable) relatively

cheaply,

Synthesize almost any material,

Co-synthesize two or more materials simultaneously,

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Coat one or more materials onto other

materials (metal or ceramic particulates, and three-dimensional objects),

Produce extremely homogeneous alloys andcomposites,

Synthesize ultra-high purity (99.9999%)

materials, Tailor the composition very accurately even in

the early stages of the process, because thesynthesis is actually performed on an atomic level,

Precisely control the microstructure of thefinal products, and Precisely control the physical, mechanical, and

chemical properties of the final products.

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In general, the sol-gel process involves the transition of asolution system from

a liquid "sol" (mostly colloidal) into a solid "gel" phase.

Utilizing the sol-gel process, it is possible to fabricate advancedmaterials in a wide variety of forms:

ultrafine or spherical shaped powders,

thin film coatings, fibers, porous or dense materials, and

extremely porous aerogel materials.

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The starting materials used in the preparation of the "sol" areusually inorganic metal salts or metal organic compoundssuch as metal alkoxides.

In a typical sol-gel process, the precursor is subjected to a seriesof hydrolysis and polymerization reactions to form a colloidalsuspension, or a "sol".

Further processing of the "sol" makes it possible to makematerials in different forms.

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a flexible method for preparation of (nano)materials

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Orgin of Ferroelectricity

* The Existence of a Double-Well Potential.

* The Formation of Ferroelectric Domains.

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permittivity ordielectric constant of a material is

H2O is a polar liquid; ~ 80

Typical ionic solids; ~ 10

Air; ~ 1

BaTiO3 :-

vacC

C

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Below 120C, BaTiO3 is ferroelectric with aligned

dipoles.

Residual dipole disorder gives ~200-1000

At ~127C, tetragonal cubic phase transition.

Dipoles randomise and increases to ~5,000-10,000

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For capacitor applications,

need to increase capacitance [energy stored/mass orvolume] by increasing Q and thus increasing

How to do this?

BaTiO3 is very good at 120C

but want high at room temperature!

1) Partial substitution of Ba by a smaller M

2+

ion - Sr

2+

;unit cell volume decreases and the phase transition temperature

decreases

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Powder preparation

Shape forming

High temperature sintering

Finishing

Pressure-less hot press

hot isostatic press

mechanical

Laser, water jet

ultrasonic

Pressing, casting

plastic forming

colloidal processing

solid-state reaction

coprecipitation

sol-gel

spray pyrolysis

emulsion synthesishydrothermal synthesis

Four steps involved in typical powder processing for advanced

ceramics.

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Synthesis method Solid-state

Reaction

Coprecipita-

tion

Sol-gel Spray

/Freeze

Drying

Spray

Pyrolysis

Emulsion

Synthesis

Hydrother

mal

Synthesis

state ofdevelopment

commercial commercial R&D demonstration

R&D demonstration demonstration

compositional

control

poor good excellent excellent excellen

t

excellent excellent

morphology

control

poor moderate moderate moderate excellen

t

excellent good

powder reactivity poor good good good good good good

particle size (nm) >1000 >10 >10 >10 >10 >100 >100

purity (%) 99.5 >99.9 >99.9 >99.9 >99.9 >99.5

agglomeration moderate high moderate low low low low

calcination step yes yes yes yes no yes no

milling step yes yes yes yes no yes no

costs low-

moderate

moderate moderate-

high

moderate-

high

high moderate moderate

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Experimental procedurePb(NO3)2 + La(NO3)3.6H2O +Bi(NO3).5 H2O +ZrO(NO3)2.2H2O

distilled water

Stirring on magnetic stirrer for 2-3 hrs to get transparent solution

Drop wise addition of Titanium isopropoxide results in formation of Ti(OH)4

Few drops of nitric acid to dissolve Ti(OH)4& to get clear solution

white precipitate was obtained

Solution was vacuum filtered and washed several times with distilled water

Filtered cake powder was kept in oven for 24 hrs at 150C

Dropwise addition of NH3OH Soln

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DTG and TG curve of sample A

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DTG and TG curves of sample B

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XRD patterns of sample A at

various temperatures () TiO2, () Pb(NO3)2, () Bi2O3, () ZrO2.

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XRD patterns of sample B at different temperatures

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XRD pattern of sintered ceramics

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d values in (Sample A)

d values in (Sample B)

h k l

Observed Calculated Observed Calculated4.128 4.129 4.113 4.114 0 0 1

4.018 4.019 4.004 4.005 1 0 0

2.876 2.880 2.872 2.870 1 0 1

2.344 2.341 2.334 2.333 1 1 1

2.064 2.064 2.063 2.057 0 0 2

2.008 2.009 2.006 2.002 2 0 0

1.836 1.836 1.836 1.830 1 0 2

1.8080 1.807 1.801 1.800 2 0 1

1.6730 1.670 1.668 1.664 1 1 2

1.647 1.648 1.646 1.642 2 1 1

1.440 1.440 1.437 1.435 2 0 2

Comparison of observed and calculated d values

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Sample System tetragonal Unit cell

Volume(3)

a () c () a/c

A 4.0197 4.1298 1.0274 66.73

B 4.0057 4.1148 1.0272 66.02

Comparison of lattice parameters

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Sample r maxEDS methodPLZT (7/65/35)

PLZT (8/65/35)

PLZT (9/65/35)

PLZT (10/65/35)

1340

1610

1430

990

2815

3465

1690

1108

Co-precipitation

PLZT (7/65/35)

PLZT (8/65/35)

PLZT (9/65/35)

PLZT (10/65/35)

2245

3480

3055

2130

5905

6890

4020

3760

Comparison of Dielectric Constants of modified PZT Ceramics

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AVersatile process for making ceramic and glass materials(powders, coatings, fibers variety of forms).

Involves converting from a liquid solution to a solid gel

Start with inorganic metal salts or metal alkoxides (called

precursors); series of hydrolysis and polymerization

reactions to prepare a colloidal suspension (sol).

Next step involves an effort to get the desirable form- thin film by spin or dip coating

- casting into a mold

Further drying/heat treatment, wet gel is converted into

desirable final product

Conclusion

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Ceramic fibers can be drawn from the gel by adjusting theviscosity

Powders can be made by precipitation, or spray pyrolysis

Examples

- Piezoelectric materials such as lead-zircomium-titanate (PZT)

- Thick films consisting of nano TiO2 particles for solar cells

- Optical fibers

- Anti-reflection coatings (automotive)