1. Dielectric Materials M V V K Srinivas Prasad

2. f28_17_pg661 M V V K Srinivas Prasad

3. f29_17_pg653 M V V K Srinivas Prasad

4. f30_17_pg663 M V V K Srinivas Prasad

8. Dipolar or orientation polarization P dip Electronic polarization P e Ionic polarization PiPi Convince yourself that when E is applied the center -ve charge is no longer coincident with the center of +ve charge.

9. f33_17_pg668 M V V K Srinivas Prasad

10. f34_17_pg668 M V V K Srinivas Prasad

12. Frequency Response (Switching Time) Electronic Polarization Ionic Polarization Orientational Polarization

13. t05_17_pg662 M V V K Srinivas Prasad

14. Comparison FactorElectronic Polarization DefinitionElectron cloud shift wrt nucleus Cations & anions are shifted Arrangement of random dipoles ExamplesInert gasesIonic crystalsAlcohol, methane TemperatureIndependent Dependent Relaxation time Very fastSlow Power lossLowHighHigher Frequency range Up to 10 15 Hzs and above Up to 10 14 Up to 10 5 M V V K Srinivas Prasad

15. FERROELECTRIC MATERIALS M V V K Srinivas Prasad

16. Exhibit electric polarisation even in the absence of electric field. Analogous to ferromagnetic materials in magnetism. Presence of permanent electric dipoles. Dielectric constant. M V V K Srinivas Prasad

17. Ferroelectricity refers to creation of enormous value of induced dipole moment in a weak electric field as well as existence of electric polarization even in the absence of applied electric field Ex : –Barium Titanate (Ba Ti O3) –Pottasium dihydrogen phosphate(N H4 H2 P O4) –Rochelle salt(Na KC4 H4 O6.4H2O) M V V K Srinivas Prasad

18. Properties Easily polarised even for small electric fields. Exhibits dielectric hysteresis. Possess spontaneous polarisation. Possess permanent electric dipole. Exhibit domain structure like ferromagnetic material. All ferroelectric materials are piezo but all piezo electric are not ferroelectric. M V V K Srinivas Prasad

19. Ferroelectrics Spontaneous polarization without external field or stress Very similar to ferromagnetism in many aspects: alignment of dipoles, domains, ferroelectric Curie temperature, “paraelectric” above the Curie temperature.... But: here direct electric field interactions. Direct magnetic field interactions were far too weak to produce ferromagnetism. M V V K Srinivas Prasad

20. Polarisation hysteresis P E M V V K Srinivas Prasad

21. Polarisation hysteresis P E M V V K Srinivas Prasad

22. Spontaneous Polarization and the Hysteresis M V V K Srinivas Prasad

25. Ferroelectric Ceramics Ferroelectric Ceramics are dipolar below Curie T C = 120ºC cooled below T c in strong electric field - make material with strong dipole moment Fig. 18.35, Callister 7e. M V V K Srinivas Prasad

26. As BaTiO 3 is cooled below 120 °C it goes from cubic to tetragonal spontaneously. The tetragonal unit cell has a permanent dipole moment that is huge, which is why most capacitors today are made from BaTiO 3 or related compounds. M V V K Srinivas Prasad

27. Example: barium titanate ferroelectric M V V K Srinivas Prasad

28. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. M V V K Srinivas Prasad

30. Perovskite Structure M V V K Srinivas Prasad

32. Piezoelectric Materials at rest compression induces voltage applied voltage induces expansion Piezoelectricity – application of pressure produces current Application of voltage produces dimensional changes