Synthesis and characterization of BaTi1-xGaxO3-delta (0x0.15) ceramics

The crystal structure type, ceramic microstructures, and dielectric properties of BaTi1-xGaxO3-delta (BTG) (0 0.12, a secondary phase isostructural with Ba2TiO4 is detected. Scanning electron microscopy (SEM) reveals three distinctive ceramic microstructures dependent on the firing temperature. BTG compacts fired at 1350 degrees C consist of fine (2-3 mu m) equiaxed grains within a narrow grain size distribution, whereas either large anisotropic or large (100-300 mu m) rounded grains embedded in a fine-grained matrix are observed for ceramics fired at 1400 degrees and 1450 degrees 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, epsilon(r), for x = 0.06 decreases continuously with x from similar to 80 to similar to 65. h-BTG ceramics show a strong decrease in epsilon(r) with increasing temperature in the range 125-425 K, suggesting the possibility of a phase transition below 125 K.