The peroviskite oxides, Sr_(1-x)Eu_xTiO_3 (x=0.0-0.5), Ba_(1-x)Eu_xTiO_3 (x=0.0-0.4), Eu_(0.56)K_(0.44)TiO_3 and La_(1-x)Na_xTiO_3 (x=0.05, 0.1 and 0.5), were synthesized by high-pressure and high-temperature. Their structure were determined by X-ray diffraction. The measurements of ~(151)Eu Mossbuaer spectra and eelctron paramagnetic resonance show that the Eu~(3+) and Ti~(4+) ions can be reduced. The valence changes of Eu and Ti ions induced by high pressure and high temperature are closely related with the structure of oxide, the size and the chanrge of other ions, as well as the atomic configuration of the ions themself. The peroviskite oxides with unusual lower valence ions would be sensitive to their environment.
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