pyro presentation
TRANSCRIPT
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