Microstructure-Dielectric Properties Relationship in Ba_(0.6)Sr_(0.4)TiO_3- Mg_2SiO_4-Al_2O_3 Composite Ceramics

摘要

0.60Ba_(0.6)Sr_(0.4)TiO_3(BST)-(0.40-x)Mg_2SiO_4(MS)-xAl_2O_3 (x = 0, 0.5, 3, 5wt%) composite ceramics exhibit excellent character-istics suitable for tunable device applications. With increasing amount of Al, the dielectric peak can be quantitatively broad-ened and suppressed; the "phase transition temperature" T_c or (T_m) shifts to a lower temperature. Meanwhile, the tunability is still high in a wider temperature range. Far from T_c, pyroelectric effects are observed by using the Byer and Roundy technology and Slim polarization hysteresis loops are observed under high ac dielectric field at 10Hz. These proved the existence of spontaneous polarization in certain possible orientations in a broad temperature range above T_c in the paraelectric medium and reveal why 0.60BST-(0.40-x)MS-xAl_2O_3 have such remarkable dielectric nonlinearity.