New pyrochlore type semiconducting ceramic oxides: Ca3Ce3-xBixTi7Nb2O26.5(x=0.5, 1.0, 2.0, or 3.0) - structure, microstructure and electrical properties

Abstract

Oxides of the pyrochlore family have a general formula A2B2O7 and they have been extensively studied because of their wide spectrum of physical properties including electrical, magnetic, optical, dielectric, and catalytic behavior. During the investigation, prepared pyrochlore type oxides in the quarternary Ca-R-Ti-Nb-O oxide system. Ca3Y3Ti7Nb2O26.5 is colorless and insulating, but when Y3+ is completely replaced by Ce4+,the compound retains the pyrochlore structure, but is black and semiconducting. Electrical conductivity in this compound is probably due to the presence of Ce3+, which remains in the reduced state without being oxidized to Ce4+ by structural stabilization (Ce4+will hold more oxygen than can be accommodated by the structure).The compounds Ca3Ce3−xBix Ti7Nb2O26.5(x = 0.5, 1.0, 2.0, 3.0) have been synthesized and characterized. The XRD patterns show the formation of pyrochlore structure. SEM pictures reveal well-grown grain structures. The electrical conductivity studies on these compounds indicate that Bi incorporation decreases the conductivity and also increases the activation energy of the conduction process. These semiconducting oxides may be useful in active and passive electronic applications.