Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Stability Phase-Fields in the and Pyrochlore Formation in Sections of the Bi2O3-Al2O3-Nb2O5

Published

Author(s)

Terrell A. Vanderah, Jorge T. Guzman, Juan C. Nino

Abstract

Bismuth niobate-based ceramic materials are of interest for embedded elements such as capacitors, resonators, and filters because they exhibit high relative dielectric permittivities and tend to be processible at temperatures in the 1000 C to 1200 C range. As part of ongoing studies of phase equilibria and structure-property relations in this class of electroceramics, the Bi2O3-Al2O3-Nb2O5 system has been determined. In contrast to published reports, we did not observe the formation of pyrochlore, despite detailed syntheses which included controlled heatings up to and above the solidus. Except for solid solutions of Al2O3 in binary Bi2O3-Nb2O5 phases (i.e. fluorite-type Bi3NbO7 and Bi5Nb3O15), no distinct ternary compounds were found in the Bi-Al-Nb-O system. Al2O3 was found to substitute for Fe2O3 in the Bi-Fe-Nb-O pyrochlore up to 30 mol%, resulting in a slight decrease in the cubic unit cell volume. The presence of Al3+ modified the dielectric properties of the Bi-Fe-Nb-O pyrochlore by increasing the relative permittivity from 125 to approximately 135 (1 MHz, 225 K), and by lowering the temperature of onset of conductive effects (from 350 K to 225 K).
Citation
Journal of the American Ceramic Society
Volume
91
Issue
11

Keywords

Bi-Al-Nb-O, Bi2O3-Al203-Nb2O5, dielectric relaxation, phase diagram, pyrochlore
Created May 8, 2008, Updated February 19, 2017