Pb valence in iron garnets

A model for the incorporation of Pb in garnets is presented in which self-compensation occurs via the formation of Pb2+ and Pb4+ and allows an explanation of the following observations: high levels of Pb substitution achievable, the temperature dependence of Pb incorporation, lattice mismatch behavior of epitaxial films of Pb-doped iron garnets, the Pb-induced uniaxial anisotropy behavior in EuIG : Pb, the electrical conductivity type, and the high Pb-induced optical absorption. Spectroscopic evidence for the simultaneous existence of Pb2+ and Pb4+ in Y3Ga5O12 (YGG) is given and analyzed in terms of Pb2+, Pb4+ impurity levels lying respectively 1.1 eV above the valence band and 2.36 eV below the conduction band. Intervalence transition between Pb2+ and Pb4+ occurs at 18 000 cm−1 (2.23 eV) in YGG : Pb. Using the separation of Pb2+ and Pb4+ levels determined in YGG and a simple energy-band model for YIG the Pb-induced absorption processes in YIG : Pb are enumerated and shown to give a qualitative explanation of the absorption spectrum of YIG : Pb.