An electron paramagnetic resonance investigation was made of Rh impurities in thermally reduced crystals at 90K. The electron paramagnetic resonance spectra were attributed to two Rh centers. It was proposed that the corresponding defects were Rh2+ ions which substituted for Ti in the two Ti sites of the structure. The spin-Hamiltonian parameters were analyzed, and possible mechanisms which accounted for the distortion around the impurity were proposed. Heat treatment in vacuum produced a marked increase in the observed electron paramagnetic resonance spectra. It was concluded that most Rh impurities entered the material as Rh3+ ions.

D.Bravo, M.J.Martín, J.Gavaldá, F.Díaz, C.Zaldo, F.J.López: Physical Review B, 1994, 50[22], 16224-31