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The Crystal Structure of LaAlO3-Stabilized La2/3TiO3 Ceramics: An HRTEM Investigation
Authors:Feridoon Azough  Wenjin Wang  Robert Freer
Affiliation:Materials Science Centre, School of Materials, University of Manchester, Manchester M1 7HS, U.K.
Abstract: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 (?r) 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 ≈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.
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