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FERROELECTRIC CERAMICS: properties, processing and applications

FERROELECTRIC CERAMICS: properties, processing and applications. Er. GAJENDRA SINGH & GURMEET SINGH 15 january 2010. Introduction . A ferroelectric ceramic mixes the smartness of a ferroelectric material and the tailoring possibilities of ceramics.

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FERROELECTRIC CERAMICS: properties, processing and applications

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  1. FERROELECTRIC CERAMICS:properties, processing and applications Er. GAJENDRA SINGH & GURMEET SINGH 15 january 2010

  2. Introduction • A ferroelectric ceramic mixes the smartness of a ferroelectric material and the tailoring possibilities of ceramics. • Since both kind of materials exhibit many interesting properties, the mixture should be good…

  3. Ferroelectrics: ferroelectric domains • Ferroelectric domains are generated by coupling between dipole moments of atoms. • When subjected to electric field, the domains pointing towards its direction start to grow over its neighbouring domains.

  4. Ferroelectrics: hysteresis loop • Saturation and remanent polarization • Coercive field • Possibility to reverse the polarization • Smart material: it keeps information (remanent poalrization)

  5. Ferroelectrics: phase transition • Ferroelectricity is a phase transition (Curie point) • Ferroelectric phase has always lower symmetry • Example: BaTiO3 (cubic changes into tetragonal)

  6. Ferroelectrics: summary • Present spontanous polarization • Polarization can be inversed • Ferroelectric domains • Hysteresis loop • Ferroelectricity is a phase transition • Piezoelectric and pyroelectric effect

  7. Ceramics is a wide term… • The term ceramics covers all inorganic non-metallic materials whose formation is due to the action of heat. • So you could think something like this…

  8. …but we are dealing with ADVANCED ceramics! We can control, modify and optimize its properties by tailoring the material!

  9. Properties of ceramics • Mechanical: poor toughness (under study) • Electrical: semiconductors, superconductors, piezoelectrics, pyroelectrics, ferroelectrics (BaTiO3, PZT…) • High resistance to abrasion • Excellent hot strength • Chemical inertness • We can tailor properties for specific applications

  10. FERROELECTRICS High permittivities Spontaneus polarization Electric conducticity can be controlled Piezoelectric and pyroelectric effect Optical anisotropy, electrooptic an photorefractive deffect CERAMICS Broad range of chemical composition Control of grain size, porosity… Possibility of varying its shape and size. High resistance to abrasion Excellent hot strength Chemical inertness Why are ferroelectric ceramics so important? All this properties lead to a lot of potential applications!

  11. 2.Processing of Ferroelectric ceramics

  12. Raw Materials Mixing 1. General Procedure of Processing • Calcining • Character -ization • Milling • Poling • Sintering • Binder Burnout

  13. 1. raw materials Weighing the raw materials according to the stoichiometric formula of the ferroelectric ceramic desired .

  14. Mixing the powders either mechanically or chemically Mechanical mixing is usually done by either ball milling or attrition milling for a short time. Chemical mixing on the other hand is more homogeneous as it is done by precipitating the precursors in the same container. 2. Mixing

  15. The solid phase reaction takes place between the constituents giving the ferroelectric phase during the calcination step 3.Calcination

  16. 4. Milling The lumps are ground by milling after calcining.

  17. 5. binder burnout After shaping, the green bodies are heated very slowly to between 500-600° C in order to remove any binder present.

  18. 6.Sintering • After the binder burnout is over, the samples are taken to a higher temperature for sintering to take place.

  19. 7.Poling • it does not show any piezoelectricity when the ferroelectric ceramic is cooled after sintering . Piezoelectric behavior can be induced in a ferroelectric ceramic by a process called "poling" . • In this process a direct current (dc) electric field with a strength larger than the coercive field strength is applied to the ferroelectric ceramic at a high temperature, but below the Curie point.

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