The Crystal Structure of LaAlO3-Stabilized La2/3TiO3 Ceramics: An HRTEM Investigation

LaAlO₃-stabilized La_2/3TiO₃ (LT) ceramics were prepared by the conventional mixed oxide route. Small amounts of manganese oxide were added to eliminate Ti⁴⁺ reduction. The powders were calcined at 1150°C and sintered at 1400°–1500°C for 4 h and cooled at rates of 900°–15°C/h. The products were high density and single phase, with an average grain size of 6 μm. The LaAlO₃-stabilized LT ceramics exhibited a relative permittivity (?_r) of 64, a positive temperature coefficient of resonant frequency (τ_f) of 84, and dielectric Q value × resonant frequency ( Q × f ) values of 16 400 GHz. The crystal structure and microstructures have been investigated using high-resolution transmission electron microscopy (HRTEM) in conjunction with X-ray diffraction (XRD). One candidate crystal structure, a ≈2 a _p (where a _p is the lattice parameter of the high-temperature form of the cubic perovskite), b ≈2 a _p, and c ≈2 a _p with a space group Cmmm (65), has been confirmed by XRD, electron diffraction, and lattice imaging techniques. Microtwins, with twin boundaries parallel to the {100} planes, were observed in the microstructures.