3. Pyroelectric and ferroelectric sensors

Some materials naturally possess a spontaneous polarization that varies with temperature and can be reversed by the application of an electric field. These materials are called pyroelectric, and their properties can be explained by their crystalline structure, which is such that dipoles naturally exist due to the non-coincidence of the centers of gravity of positive and negative charges. Spontaneous polarization P _s thus appears, and varies with temperature, as a result of the changes that temperature brings about in the crystalline structure and, in particular, in the size of the crystal lattice. The temperature behavior of the spontaneous polarization is shown on 5 .

Pyroelectric materials can therefore be used to...