Laser Induced Reduction and Etching of Oxidic Perovskites
In oxidic perovskites like SrTi03, BaTi03,etc. oxygen vacancies can easily be produced by first heating the material in a reducing atmosphere, e.g. in hydrogen atmosphere, up to several hundred degrees and then quenching it to room temperature. The concentration of vacancies increases with increasing reduction temperature and with decreasing oxygen partial pressure. The oxygen vacancies act as shallow donor levels and the originally insulating material (band gap typically 3eV) becomes a n-type semiconductor; the originally transparent material changes to a blue or black colour, depending on the concentration of vacancies ⌊1,2⌋. Because of the fundamental role of the oxygen ion in connection with the dynamical properties of perovskites, the oxygen vacancies also strongly influence the ferroelectric and non-ferroelectric structural phase transitions observed in these materials ⌊3,4⌋.
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