Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

Valasek, 1921

From Megaw, Ferroelectricity in Crystals.

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

Hydrogen-bonded ferroelectricityin Rochelle’s salt.

From Megaw, Ferroelectricity in Crystals.

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

From Megaw, Ferroelectricity in Crystals.

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

From Megaw, Ferroelectricity in Crystals.

Hydrogen-bonded ferroelectricity in potassium dihydrogen phosphate (KDP).

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

From Megaw, Ferroelectricity in Crystals.

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

From Megaw, Ferroelectricity in Crystals.

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Eg

A1g Splitting of the structural soft mode (Raman active below Ta)

Ta

Class 9: Polar materials and ferroelectrics Antiferrodistortive transition in SrTiO3 in R-point of the Brillouin

zone

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Ferroelectric SM

Structural SM (doublet)

Mode frequencies on STO ceramics

(Petzelt et al., PRB 64, 184111 (2001))

Class 9: Polar materials and ferroelectrics

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Class 9: Polar materials and ferroelectrics

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

SrTiO3 ceramicsClass 9: Polar materials and ferroelectrics

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

0 50 100 150 200 250 300

1000

10000

SrTiO3

Temperature (K)

ε 0Experiment:

crystal (Hyper-Raman) 2 μm-grained ceramics (BWO) 2 μm-grained ceramics (MW) 100 nm-grained ceramics (diel. meas. 100 kHz)

Theoretical model: 2 μm-grained ceramics, eps(GB)=100, ξ= 7 nm 100 nm grained, eps(GB)=100, ξ= 7 nm

Class 9: Polar materials and ferroelectrics

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Order-disorder model forBaTiO3 phase transitions

Class 9: Polar materials and ferroelectrics

Dynamically disordered Ti

Ordered Ba

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

0 200 400 600 800 1000 1200 14000

20406080

100120140160180200220240260280

CTR O

E

E

Freq

uenc

y (c

m-1)

Luspin_80 (IR refl.) Vogt_82 (HR) Laabidi_90 (R) Perry_65 (R) Burns_78 (R) Dougherty_94 (femt. ISRS)

Temperature (K)

B2

B1?

A1

F1u

TO1 mode in BaTiO3 single crystal

Class 9: Polar materials and ferroelectrics

Materials 286 G: Structural Families of Functional Inorganic MaterialsRam Seshadri x6129 seshadri@mrl

Unpolarized Raman spectra of BaTiO3 crystals (after Perry and Hall 1965)

Wavenumber (cm-1)

Class 9: Polar materials and ferroelectrics

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