Microstructure and Dielectric Properties of a LaAlO ₃ –TiO ₂ Diffusion Couple

Near‐field scanning microwave microscopy was applied to investigate the dielectric properties and microstructure in a polycrystalline LaAlO 3 –TiO 2 diffusion couple, which included three regions containing different phases and microstructures. Relatively low (La 2 Ti 4 Al 18 O 38 ), high (α‐La 2/3 TiO 3 ), and intermediate (La 4 Ti 9 O 24 ) dielectric constant phases were distinguished at the inter‐diffusion interface in optical, backscattered electron scanning electron microscopy, and scanning microwave microscopy (SMM) images. The relative ranking of dielectric constants based on SMM examination was as follows: TiO 2 >α‐La 2/3 TiO 3 >La 4 Ti 9 O 24 >LaAlO 3 >La 2 Ti 4 Al 18 O 38 . La 2/3 TiO 3 and LaAlO 3 will form solid solutions in the LaAlO 3 ‐rich region. The reaction paths leading to phase development are discussed.