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The Crystal Structure of LaAlO 3 ‐Stabilized La 2/3 TiO 3 Ceramics: An HRTEM Investigation
Author(s) -
Azough Feridoon,
Wang Wenjin,
Freer Robert
Publication year - 2009
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2009.03161.x
Subject(s) - high resolution transmission electron microscopy , materials science , microstructure , crystal structure , perovskite (structure) , lattice constant , analytical chemistry (journal) , ceramic , electron diffraction , transmission electron microscopy , temperature coefficient , grain size , crystallography , mixed oxide , mineralogy , diffraction , oxide , optics , chemistry , nanotechnology , metallurgy , composite material , physics , chromatography
LaAlO 3 ‐stabilized La 2/3 TiO 3 (LT) ceramics were prepared by the conventional mixed oxide route. Small amounts of manganese oxide were added to eliminate Ti 4+ 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 LaAlO 3 ‐stabilized LT ceramics exhibited a relative permittivity (ɛ 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.