Defect property correlations in garnet crystals. II. Electrical conductivity and optical absorption in Ca3Al2Ge3O12

Electrical conductivity and ionic transference measurements performed at varying temperatures and partial pressures of oxygen show that CALGAR (Ca3Al2Ge3O12), a luminescent garnet, is a mixed ionic-electronic conductor. An activation energy of 1 eV for ionic diffusion is measured. An absorption band at 400 nm, whose magnitude can be controlled by varying the annealing atmosphere, is attributed to an O− center.