Electron Paramagnetic Resonance of Copper in Beryllium Oxide

Paramagnetic-resonance absorption of copper-doped single crystals of beryllium oxide has been investigated at 9 GHz. The best-fit values to a spin Hamiltonian with S=1/2 are |g_∥|=1.709±0.002, |g_⊥|=2.379±0.001, |A_∥|=(50±1)×10^-4 cm^-1, |A_⊥|=(108±1)×10^-4 cm^-1, and |Q|=(11±1)×10^-4 cm^-1, where the hyperfine values refer to the Cu⁶³ isotope, for which I=3/2. The observations are interpreted as due to Cu²⁺ substitutional for beryllium at normal lattice sites. Crystal-field theory which incorporates covalent bonding has been used to interpret these results in terms of the 3d⁹ configuration of Cu²⁺ in C₃ᵥ symmetry. The experimental results are shown to be consistent with the theory, which yields an orbital reduction factor of 0.6, and values for 〈r^-3〉 and the contact hyperfine interaction close to those for the free ion. The results are also compared with some other cases of 3d⁹ ions in tetrahedral coordination.