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The EPR spectra of Fe + in the three ferroelectric phases of BaTi03 could be interpreted on the basis of the Newman superposition model. In the latter, the position of the nearest (oxygen) ligands determines the EPR spectrum. It is found that the Fe + participates by less than an order of magnitude in the collective motion of the Ti4+ ions out of their inversion symmetric position: by centering the Fe + and using previously determined intrinsic oxygen coordinates and parameters of the Newman model, the sign and magnitude of the EPR b20 terms could be obtained for (a). the tegragonal phase, (b) the tetragonal (001) spectrum perpendicular to the (110) polarization in the orthorhombic phase, and (c) the very small (111) splitting in the rhombic phase; the electronic polarization being of the same magnitude in all three phases. The centered Fe + also yields correct EPR b2 parameters for PbTi03 and KNb03. The investigation shows that the Fe + is a very sensitive probe of the intrinsic oxygen positions. The small coupling of the Fe3+ to the off-center ferroelectric motion is ascribed to its half-filled 3d shell.

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