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Synthesis and Characterization of BaTi 1− x Ga x O 3−δ (0 x 0.15) Ceramics
Author(s) -
Feteira Antonio,
Sinclair Derek C.,
Reaney Ian M.
Publication year - 2006
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.1551-2916.2006.00982.x
Subject(s) - materials science , microstructure , ceramic , curie temperature , analytical chemistry (journal) , tetragonal crystal system , dielectric , crystallography , scanning electron microscope , grain boundary , mineralogy , crystal structure , composite material , chemistry , ferromagnetism , condensed matter physics , physics , optoelectronics , chromatography
The crystal structure type, ceramic microstructures, and dielectric properties of BaTi 1− x Ga x O 3−δ (BTG) (0 x 0.15) ceramics prepared by the mixed oxide route have been investigated. X‐ray diffraction shows the room‐temperature crystal structure of BTG changes from tetragonal ( t ‐BT; space group P 4 mm ) to hexagonal ( h ‐BT; space group P 6 3 / mmc ) at x ∼0.04. These results are also confirmed by electron diffraction and dielectric measurements. For x >0.12, a secondary phase isostructural with Ba 2 TiO 4 is detected. Scanning electron microscopy (SEM) reveals three distinctive ceramic microstructures dependent on the firing temperature. BTG compacts fired at 1350°C consist of fine (2–3 μm) equiaxed grains within a narrow grain size distribution, whereas either large anisotropic or large (100–300 μm) rounded grains embedded in a fine‐grained matrix are observed for ceramics fired at 1400° and 1450°C, respectively. Transmission electron microscopy (TEM) of BTG ( x =0.04) ceramics reveals some grains exhibiting both ferroelectric domains and stacking faults, which appear absent in ceramics with x ≥0.06. Ga‐enriched grain boundaries were also revealed by energy dispersive spectroscopy (EDS) analysis. Dielectric measurements show the room‐temperature relative permittivity, ɛ r , for x ≤0.03 to be ∼1500–2000 and that the Curie Temperature, T c , decreases at a rate ∼8 K/at.%, whereas the room‐temperature ɛ r for h ‐BTG with x ≥0.06 decreases continuously with x from ∼80 to ∼65. h ‐BTG ceramics show a strong decrease in ɛ r with increasing temperature in the range 125–425 K, suggesting the possibility of a phase transition below 125 K.