The crystal structure of LaAlO3-stabilized La 2/3TiO3 ceramics: An HRTEM investigation

LaAlO3-stabilized La2/3TiO3 (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 (εr) of 64, a positive temperature coefficient of resonant frequency (τf) 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≈2ap (where ap is the lattice parameter of the high-temperature form of the cubic perovskite), b≈2ap, and c≈2ap 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. © 2009 The American Ceramic Society.