Weiss domains

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Charge separation between the positive and negative ions is the reason for electric dipole behavior. Groups of dipoles with parallel orientation are called Weiss domains. The Weiss domains are randomly oriented in the raw piezoelectric material, before the poling treatment has been finished. For this purpose an electric field (> 2000 V/mm) is applied to the (heated) piezo ceramics. With the field applied, the material expands along the axis of the field and contracts perpendicular to that axis. The electric dipoles align and roughly stay in alignment upon cooling. The material now has a remanent polarization (which can be degraded by exceeding the mechanical, thermal and electrical limits of the material). As a result, there is a distortion that causes growth in the dimensions aligned with the field and a contraction along the axes normal to the electric field.

When an electric voltage is applied to a poled piezoelectric material, the Weiss domains increase their alignment proportional to the voltage. The result is a change of the dimensionss (expansion, contraction) of the piezoelectric material.

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