Preparation, structure and dielectric properties of bismuth-based ceramic dielectrics

Samples of 0.75Bi/sub 2/O/sub 3/-ZnO-0.75A/sub 2/O/sub 5/ (A=Nb, Ta) were prepared by conventional ceramic technology, sintered below 1000/spl deg/C. Based on X-ray diffraction analysis, the structure of 0.75Bi/sub 2/O/sub 3/-ZnO-0.75Nb/sub 2/O/sub 5/ (BZN) composition is characterized as cubic pyrochlore, while the 0.75Bi/sub 2/O/sub 3/-ZnO-0.75Ta/sub 2/O/sub 5/ (BZT) composition is a multiphase ceramic with two cubic fluorites and an orthorhombic pyrochlore structures. The bismuth-based ceramic dielectrics have excellent electrical resistivity greater than 10/sup 14/ ohm-cm. The BZN dielectric has dielectric constant around 130, the room temperature dissipation factor is less than 4/spl times/10/sup -4/ from 10 KHz to 1 MHz, and the temperature coefficient of the dielectric constant is about -470 ppm//spl deg/C. For the BZT composition, the dielectric constant decreases to 80, the dissipation factor deteriorates to 5/spl times/10/sup -3/, and the temperature coefficient increases to +60 ppm//spl deg/C.