We present the results of computer simulation studies of SrTiO,. After deriving a reliable potential model, we concentrate on the properties of defects and dopants. Our calculations are used to propose a defect model that is consistent with experimental observations. For vacancy disorder, the calculations show that SrTiO, (Schottky) and SrO (Schottky-like) disorder have very similar energy, with a small tendency for the development of Sr deficiency at higher temperatures. All mono-and divalent cations prefer to substitute at strontium sites. For trivalent cations, three types of mechanism (Sr and Ti substitution and selfcompensation) are proposed, whereas for tetravalent cations substitution on both A and B sites may occur, depending on the ionic radius.

AbstrPet me valencesate of Bi in pure and doped (F'b. K) B a B i a has been delermined by x-ray absorption near-edge srmnure (XANES) spenmscopy. in all materials l k Bi valence is found U) be close U) IV. A dispmpnionation of Bi(1V) into Bi(ll1) and Bi(V) is not indicated by analysis of the XANES daLz The valence sue of F'b is also found U) be IV in BaBir-,Pb,O~.

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