Pb valence in iron garnets

Abstract

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.