Synthesis and dielectric properties of pyrochlore solid solutions in the Bi2O3-ZnO-Nb2O5-TiO2 system

Phase studies of solid solutions based on (Bi1.5Zn0.5)(Ti1.5Nb0.5)O-7 revea led extended regions of pyrochlore formation in the Bi2O3-ZnO-TiO2-Nb2O5 sy stem. At room temperature and 1 MHz (Bi1.5Zn0.5)(Ti1.5Nb0.5)O-7 has a high permittivity (kappa' = 200), low dielectric loss (tan delta < 1 . 10(-4)) a nd a temperature coefficient of the permittivity, tau(kappa'), = -1300 ppm/ K. Pyrochlore solid solutions based on (Bi1.5Zn0.5)(Ti1.5Nb0.5)O-7 can be f ormed with (Bi-2- xZn(x))(Ti2- x Nb-x)O-7 (0.35 less than or equal to x les s than or equal to 1.0) and with (Bi-1.5 Zn0.5- y/3Ti1.5+yNb0.5-2y/3) O-7 ( -1.5 less than or equal to y less than or equal to 0.75). Investigations of the dielectric characteristics showed that the high temperature dependence of the permittivity of (Bi-1.5Zn(0).5)(Ti-1.5Nb(0).5)O-7 can be significan tly modified by changing the composition of the pyrochlore within these reg ions of solid solubility. Below room temperature several of these compositi ons also exhibit a diffuse frequency dependent maximum in their permittivit y characteristic of a transition to a relaxor type ferroelectric state. A t hird region of high permittivity pyrochlores with (Bi1.5+2zZn0.25-zTi2.25-z )O-7 (0.0 less than or equal to z < 0.15) was also identified in the Bi2O3- ZnO-TiO2 sub system. (C) 1999 Kluwer Academic Publishers.