Domain clamping effect

Some of the piezoeleetric materials are being used in applieations in the form of thin films of various thieknesses. The physieal situation is somewhat different from bulk materials. For example the electrode layer thickness is of comparable size with the thickness of piezoelectrically active film. If the film is deposited on the substrate the mechanical clamping is significant. Clamping could influence the film effective properties and the domain stracture for ferroelectric substances. Material coefficients are not usually completely available in the hterature because of the specific geometry and they depend on film thickness. Material properties of thin films are different from the bulk properties of the same material. Especially the size effect could result in loss of ferroelectricity below certain film thickness. Lower limit for the ferroelectricity is not generally known for all materials. 

The progress made to date in the application of domain information from oxide single crystals to the behavior in the ceramic is severely limited. The differences are essentially connected with the spread of spontaneous polarization and cell anisotropy due to clamping, impurity segregation at crystallite boundaries, and the effects of limited crystallite size. In the ideal circumstance... 

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