Effect of La/Sn co-substitution for Ba/Ta on crystal structure and dielectric properties of Ba{sub}5NdTi{sub}3Ta{sub}7O{sub}30 ceramics

摘要

The effects of La/Sn co-substitution for Ba/Ta were investigated for the modification of Ba{sub}5NdTi{sub}3Ta{sub}7O{sub}30 ceramics. The modified ceramics (Ba{sub}(5-x)La{sub}x)NdT{sub}i3(Ta{sub}(7-x)Snx)O{sub}30 exhibited single tetragonal tungsten bronze phase for x< 1.5, while a small amount of secondary phase BaTi{sub}4O{sub}9 was observed for x > 1.5. The lattice constants decreased with increasing La/Sn content, while the axial ratio 10{sup}(1/2)c/a decreased when x was below 1.5, then slightly increased. With increasing La and Sn content, the temperature coefficient of dielectric constant (at 1 MHz) was remarkably lowered from - 1560ppm/℃ to - 286 ppm/℃, while the dielectric constant gradually reduced, and the dielectric loss slightly increased. There were some clear relationships between the temperature coefficient and bond valence, tolerance factor: the temperature coefficient of dielectric constant linearly increased when the bond valence of the ions at B sites increased, while the same effect occurred when the tolerance factor decreased. In addition, the stability of the tetragonal tungsten bronze phase is discussed in relation to electronic difference and tolerance factor.