5.5 Pyroelectric Ceramics

Pyroelectric materials possess a spontaneous polarization along a unique crystallographic direction which may or may not be reversible by changing the polarity of the applied field. If the latter is true, then a pyroelectric material is also ferroelectric. If it is ferroelectric material too, then the material can either be in a single crystalline state or in a poled state.

Pyroelectricity, in itself, is the ability of materials to generate a voltage when they are heated or cooled. It is temperature dependence of the spontaneous polarization in polar materials due to minute changes in the atomic positions as a result of change in the temperature. If the temperature is constant, then voltage gradually disappears due to leakage of charges through the material or air or the apparatus.  Change in the polarization on a sample surface can be measured as an induced current.

Pyroelectricity was first observed by the Greek philosopher Theophrastus in 314 BC who found that Tourmaline attracted small pieces of straw and ash when it was heated. The first scientific description of this phenomenon was described  by Louis Lemery  in 1717. In 1747, Linnaeus first related the phenomenon to electricity, although this was not proven until Franz Ulrich Theodor Aepinus did so in 1756.