**4.1.1 Optical properties**

For non-metallic materials it is often possible to obtain UV/VIS spectra. In the case of semiconductors that will give an idea of the band gap. Surfaces of *AB*O3 perovskites and defects therein are extremely relevant for such important fields of technology as photocatalysis, gas-sensors and for applications as materials for ferroelectric memories, and the optical properties of them can be proved to be extremely interesting.
