Microstructure and microsegregation in substrate garnet materials

Electron microscopy is used to study the microstructure of gadolinium gallium garnet (GGG) and calcium gallium germanium garnet (CGGG), materials used as substrates for bubble garnet films. Isolated undissociated dislocations with Burgers vectors (1/2) 〈111〉 are characterized using dynamical contrast analysis. Microcracks (≲1 μ in size) bounded by groups of dislocations are observed in both GGG and CGGG. The occurrence of small inclusions (and voids) in CGGG are also investigated. A model is developed to explain the formation of these precipitates due to microsegregation of vacancy-atom clusters.