Abstract
Approaching to defect chemistry of electronic perovskite ceramics using high-resolution transmission electron microscopy and first-principles (ab-initio) pseudopotential total energy calculations effectively clarified new type of defect structures and its special features.
(1) In A-site-excess (Sr, Ca)TiO3, bulk-ceramics, RP faults formation and preferential Ca-occupation of cation sites in the rocksalt structure of RP faults can be theoretically predicted. And the selective site occupation elucidates the empirical results, such as drastic changes of dielectric properties without contradiction.
(2) Dislocation loops with Burgers vectors of type 1/2 ‹100› were observed in non-stoichiometric and stoichiometric chemical composition alkaline earth perovskite ceramics. The dislocation loops appeared in A-site-excess and stoichiometric (Ba, Ca) TiO3 sample entirely disappeared by electron beam irradiation, may be due to the Ca ion selective site occupation and promoting diffusion of ions into the perovskite structure, while the loops in B-site-excess and stoichiometric sample transformed into a crystallographic shear structure with a 1/2 ‹100› shear vector during electron beam irradiation.
(3) Peculiar planar defect structures never have been reported were observed and characterized in nonstoichiometric SrTiO3 and BaTiO3 thin films epitaxially grown on SrTiO3 single crystal by a low-temperature deposition process, can be interpreted as metastable defect structures originating from the thermodynamically non-equilibrium growth conditions.
