In 1880 Jacques and Pierre Curie discovered that when deformed under mechanical stress, quartz crystals become electrically positively and negatively charged on prism-shaped surfaces. They called this behaviour the piezoelectric effect.
The reversal of this effect is called the inverse piezoelectric effect, i.e. the same materials undergo dimensional change under the influence of an electric field.
Above a certain temperature, the so-called Curie temperature, these kinds of materials possess a cubic elementary cell with a centre of symmetry. The main areas of the positive and negative charges are found in the centre of the elementary cell of the crystal. The materials are paraelectric. There is no detectable piezoelectric effect.
The piezoelectric properties of the ceramics important for industry are only produced by this polarisation process. In this case, the ceramics are exposed to a very strong electric field.