ESR Study of Cu 2+ Diffused into Sodium β″‐Alumina

ESR spectra due to Cu 2+ ions diffused into sodium β″‐alumina are studied. The symmetry of the spectra place the Cu 2+ ions at the mid‐oxygen sites of the conduction planes. The complex spectra are a superposition from several different configurations of ions around this site which change as a function of the amount of annealing time. The angular variations of the spectra can be divided into two main types; an anisotropic site symmetry with spin‐Hamiltonian parameters g ∥ ≈ 2.355, g ⟂ ≈ 2.087, A ∥ ≈ 12.0 mT, A ⟂ ≈ 2.0 to 4.0 mT, and a more isotropic site symmetry with g ∥ ≈ 2.003, g ⟂ ≈ 2.240, A ∥ ≈ 9.9 mT, A ⟂ ≈ 8.8 mT. These spectra are only visible at liquid‐helium temperatures. In addition an anisotropic, random‐type spectrum is observed to replace the Cu 2+ spectra at the temperature of annealed crystals is increased. This is attributed to thermal motion of the Cu 2+ ions due to their weak binding to the site.