Observations on structural evolution and dielectric properties of oxygen-deficient pyrochlores

Non-stoichiometric ceramics with the series oxygen-deficient pyrochlore in Bi2O3-ZnO-Nb2O5 ternary system was investigated to obtain structural information. Crystal structure and dielectric properties of the group of Bi1.5-2xZn1+2xNb1.5O7-x (with x = 0-0.3) compositions have been studied. The compounds departured badly from stoichiomeric compositions lead to structural distortion and unbalance of pyrochlore phase, till secondary phase occurs for x = 0.3. It can be inferred from Raman spectra that the concentration and ratio of species occupied B site is stable, while those of species occupied A site vary between the series compositions. It is reasonable to reckon that zinc dominantly occupies B site in pyrochlore structure with compositions varying. The experimental results show that dielectric constant (epsilon) decrease linearly while the temperature coefficient of dielectric constant (alpha(epsilon)) effectively increases with increasing of the x-value. Crystal distortion and structural defect resulting from chemical composition unbalance bring on the change of dielectric properties for the small x-value. (C) 2004 Published by Elsevier Ltd and Techna Group S.r.l.