PYROELECTRICITY:PYROELECTRICITY:An OverviewAn Overview

Presented by:Presented by:

RAHUL VAISHRAHUL VAISH

OutlineOutline

Introduction.Introduction. Pyroelectric materials overview.Pyroelectric materials overview. Pyroelectric contributions.Pyroelectric contributions. Pyroelectric polymer, composites, and glass ceramics.Pyroelectric polymer, composites, and glass ceramics. Measurement of the pyroelectric coefficient.Measurement of the pyroelectric coefficient. Devices & applications.Devices & applications.

IntroductionIntroduction Pyroelectricity: Electrical response of a material to a change in Pyroelectricity: Electrical response of a material to a change in

temperature. temperature.

p= (p= (dP/dT)dP/dT)E,σE,σ

Pyroelectric materialsPyroelectric materials

Ferroelectric pyroelectric materials: Spontaneous polarization switch able by electric field e.g.BaTiO3,PbTiO3,PZT, LiTaO3,,,and TGS etc.

Non-ferroelectric pyroelectric materials: no change with electric field e.g.ZnO, CdS, and CdSe etc.In both cases net polarization can be change with mechanical stress

PyroelectricityPyroelectricity

D=D=εεE + PE + Pss

dD/dT=Edε/dT + dPs/dT

D=εE + Ps

pg=Edε/dT + p

Generalized pyroelectric coefficient True pyroelectric coefficient

In all dielectrics

Pyroelectric contributionsPyroelectric contributions

ptotal= ps +dijkcjklmαlm+

Primary pyroelectric effect

Measured @ constant strain

Secondary pyroelectric effect

Tertiary pyroelectric effect

Primary pyroelectric effects:Primary pyroelectric effects: Large & negative in Large & negative in

ferroelectric materialsferroelectric materials(Thin films, clamped polar crystals & (Thin films, clamped polar crystals &

poled ferroelectric polycrystalline) poled ferroelectric polycrystalline)

Secondary pyroelectric effects:Secondary pyroelectric effects:

ddijkijkccjklmjklmααlm lm dependentdependent

( ferroelectric composites)( ferroelectric composites)

Tertiary pyroelectric effects:Tertiary pyroelectric effects: Experimental conditionsExperimental conditions

Pyroelectric coefficient Pyroelectric coefficient vs vs

TemperatureTemperature

Follow the specific heat curveFollow the specific heat curve..

P(0) & P(T) are dipole moment at 0K and a temperature T. P(0) & P(T) are dipole moment at 0K and a temperature T.

ΔP: change in dipole moment from 0K to T.ΔP: change in dipole moment from 0K to T.

U(T): internal energy at a temperature T.U(T): internal energy at a temperature T.

U(T) α [P(T)]U(T) α [P(T)]2 2 P(0) P(0)2 2 +2P(0) ΔP+2P(0) ΔP

dU/dT =dP/dTdU/dT =dP/dT

Pyroelectric coefficient αPyroelectric coefficient α specific heatspecific heat

Pyroelectric under DC biasPyroelectric under DC bias

Possible to operate ferroelectrics at or above TPossible to operate ferroelectrics at or above Tcc.. Low lossesLow losses High FOM (p/ε)High FOM (p/ε)

Pyroelectric polymersPyroelectric polymers

Ferroelectric polymer: Ferroelectric polymer: e.g. PVDFe.g. PVDF

Poled polymer: Crystalline, semi-crystalline, and Poled polymer: Crystalline, semi-crystalline, and amorphous polymeramorphous polymer

Exhibit pyroelectricity due to space charge effects.Exhibit pyroelectricity due to space charge effects.

Charged Cellular Polymers: polymer foam of non-Charged Cellular Polymers: polymer foam of non-polar materials……..polar materials……..

Charged cellular polymersCharged cellular polymers

Piezo and pyroelectricity Piezo and pyroelectricity

are due symmetry breaking are due symmetry breaking

at macroscopic level. at macroscopic level. Void volume is a factor Void volume is a factor

101015 15 larger than unit cell volume.larger than unit cell volume. Pyroelectric coefficient is of opposite sign toPyroelectric coefficient is of opposite sign to

those of ferroelectric polymers and other those of ferroelectric polymers and other

ferroelectric materials.ferroelectric materials.

Ferroelectric like behaviourFerroelectric like behaviour

Pyroelectricity in ferroelectric/polymer composites & glass-Pyroelectricity in ferroelectric/polymer composites & glass-

ceramicsceramics Properties depend upon connectivities of active phase

AdvantagesAdvantagesEasy preparationTailoring propertiesHigh F.O.M.Piezoelectricity without pyroelectricityPyroelectricity without piezoelectricityLow density

Pyroelectricity in compositesPyroelectricity in composites

Primary pyroelectric effectPrimary pyroelectric effect+ +

Secondary pyroelectric effect:Secondary pyroelectric effect: Product property: Product property:

Piezoelectricity (ferroelectric phase) Piezoelectricity (ferroelectric phase) &&

Thermal Expansion (matrix)Thermal Expansion (matrix)(When the volumes of two phases are 0.5 approximately, the(When the volumes of two phases are 0.5 approximately, the

product effect of composites i.e., secondary pyroelectric effect reaches maximum)product effect of composites i.e., secondary pyroelectric effect reaches maximum)

Polar glass-ceramicsPolar glass-ceramics

Composites: Polar crystalline phase+glass Composites: Polar crystalline phase+glass matrixmatrix

Orientated polar crystallites+glassOrientated polar crystallites+glass

Anisotropic properties

e.g. piezoelectric & pyroelectric properties

Pyroelectric coefficient for Diphasic Composites

11ss3333 = = 22ss33 33 for both phasesfor both phases

22dd33 33 & & 22pp3 3 are zeroare zero

Multicomponent Glass-Ceramic CompositesMulticomponent Glass-Ceramic Composites(Two polar phases in glass matrix)(Two polar phases in glass matrix)

Piezoelectric without pyroelectricPiezoelectric without pyroelectric&&

Pyroelectric without piezoelectricPyroelectric without piezoelectric

In piezoelectric devices, pyroelectric noise is undesirable. In piezoelectric devices, pyroelectric noise is undesirable. (Insensitive to temperature change)(Insensitive to temperature change)

Piezoelectric noise interfaces pyroelectric signals. Piezoelectric noise interfaces pyroelectric signals. (Insensitive to mechanical vibrations)(Insensitive to mechanical vibrations)

Piezoelectric glass-ceramics which are non-pyroelectric should satisfy the relation Piezoelectric glass-ceramics which are non-pyroelectric should satisfy the relation

±±11vv11pp33 ± ±22vv22pp33=0 =0 (Ba(Ba22SiSi22TiOTiO88 + Ba + Ba22GeGe22TiOTiO88)) Pyroelectric glass-ceramics which are non-piezoelectric should satisfy the relation Pyroelectric glass-ceramics which are non-piezoelectric should satisfy the relation

±±11vv11dd3333 ± ±22vv22dd3333=0 =0 (Li(Li22O-BO-B22OO33-SiO-SiO22-ZnO)-ZnO)

composites effects.

Measurement of the pyroelectric coefficientMeasurement of the pyroelectric coefficientByer-Roundy techniqueByer-Roundy technique

ApplicationsApplications

Detection of electromagnetic radiationDetection of electromagnetic radiation Infrared ImagingInfrared Imaging RefrigerationRefrigeration Solar energy conversionSolar energy conversion Radiometry, pyrometry and thermometryRadiometry, pyrometry and thermometry

Pyroelectric devicesPyroelectric devices

Window, sensing element, and integral circuit

Window:Window: --Restricts undesirable wavelengths (optical filter).Restricts undesirable wavelengths (optical filter).

-Protects the sensing element and circuits from physical & chemical damage.-Protects the sensing element and circuits from physical & chemical damage.

Single crystals of Ge, Si, AlSingle crystals of Ge, Si, Al22OO33, and ZnS coated with MgF, and ZnS coated with MgF22,BaF,BaF22,PbF,PbF22, and CaF, and CaF22 are used as the filter for the are used as the filter for the

IR regionIR region

Sensing elements:Sensing elements: Can be thin wafer of single crystal or ceramic. Can be thin wafer of single crystal or ceramic.

High curie temperature, high figure of merit and good mechanical propertiesHigh curie temperature, high figure of merit and good mechanical properties

Compensated detectorCompensated detector

Noise or unwanted voltages due mechanical vibrations. Noise or unwanted voltages due mechanical vibrations. (all pyroelectric materials are piezoelectric)(all pyroelectric materials are piezoelectric)

Electrocaloric effectsElectrocaloric effects

Converse of pyroelectric effectConverse of pyroelectric effect Electrocaloric cooling is based on the change in temperature Electrocaloric cooling is based on the change in temperature

of a dielectric under adiabatic conditions when an external of a dielectric under adiabatic conditions when an external field is applied to and removed from it (the electrocaloric field is applied to and removed from it (the electrocaloric effect). effect).

Cooling temperature range 4-15 KCooling temperature range 4-15 K

General TdS equation for a dielectric materialGeneral TdS equation for a dielectric material

For adiabatic transformations:For adiabatic transformations:

Hence a negative dT (i.e. refrigeration) for a Hence a negative dT (i.e. refrigeration) for a negative dE, when (dp/dT)negative dE, when (dp/dT)E E is negative.is negative.

For ferroelectric materials, T<Tc; the first term is For ferroelectric materials, T<Tc; the first term is negative: much higher than second term (positive)negative: much higher than second term (positive)

T>Tc; the first term is nil and the second one is T>Tc; the first term is nil and the second one is negative.negative.

In both cases generalized pyroelectric coefficient is In both cases generalized pyroelectric coefficient is neagtive. So, Electrocrefrigeration is possible in neagtive. So, Electrocrefrigeration is possible in both cases.both cases.

Principle of electrocaloric coolingPrinciple of electrocaloric cooling

(1) Heat receiver, (2,5) thermal switches, (3) thermal (1) Heat receiver, (2,5) thermal switches, (3) thermal switches, (4) working medium, (6) heat source switches, (4) working medium, (6) heat source

AdvantagesAdvantages

Solid state refrigerator.Solid state refrigerator. Electric fields are easier to handle than Electric fields are easier to handle than

magnetic fields.magnetic fields. Needed dielectric insulations and voltage-

handling circuitry are already well-established. Will potentially save 50 kWh per year in a

typical refrigerator using 1000 kWh per year.

Thank YouThank You

Next seminar…………….Next seminar…………….

Ellipsometry : A tool for thin film characterization

Ellipsometry is a versatile and powerful optical technique for the investigation of the structural and dielectric properties (complex refractive index or dielectric function) of thin films. It has applications in many different fields, from semiconductor physics to microelectronics and biology, from basic research to industrial applications. As an optical technique, spectroscopic ellipsometry is non-destructive and contactless and can yield information about layers that are thinner than the wavelength of the probing light itself, even down to a single atomic layer or less. Ellipsometry can probe the complex refractive index or dielectric function tensor, which gives access to fundamental physical parameters and is related to a variety of sample properties, including morphology, crystal quality, chemical composition. It has been used to characterize the surface roughness and interface thickness of multilayer thin film ranging from a few angstroms or tenths of a nanometer.

In this talk, I’ll disscuss the basic principle behind working of ellipsometer and its utilisation to determine the interfacial roughnesss in multilayer thin films. I will also show some of our results obtained on pulsed laser deposited thin films.

By Neelam Kandwal