Synthesis of Zn and Mn Co-Doped Bismuth Tantalate Pyrochlore Type Ceramics

Abstract

Bi₂Zn_xMn_1–xTa₂O_9.5–∆ ceramics were synthesized for the first time using the solid phase synthesis method. The samples were found to contain cubic pyrochlore (sp. gr. Fd–3m) as the main phase and a triclinic modification (sp. gr. P-1) of BiTaO₄ as admixture. The amount of the triclinic modification is proportional to the manganese content in the samples. The formation of impurities is associated with the distribution of a fraction of the transition element ions into the cationic sublattice of bismuth (III). The unit cell parameter of the pyrochlore phase increases with increasing content of zinc ions in the samples from 10.4895(5) Å (x = 0.3) to 10.5325(5) Å (x = 0.7) in accordance with the Vegard rule. The formation of impurities in samples can be prevented by creating a bismuth ion deficiency in the bismuth sublattice by an amount proportional to the β-BiTaO₄ content. The unit cell parameter of single-phase pyrochlores Bi_2–yZn_xMn_1–xTa₂O_9.5–∆ synthesized in this way increases with increasing zinc ion content in the samples from 10.4764(5) Å (x = 0.3) to 10.5122(5) Å (x = 0.7). As observed through electron scanning microscopy, the ceramic samples exhibit a low-porosity microstructure with indistinct grain boundary outlines. The porosity of the samples decreases as the zinc content of the samples increases. The formation of a deficient bismuth sublattice during preparation is associated with a more porous microstructure, which can be attributed to a reduced concentration of the readily fusible component present in the reaction mixture, namely bismuth (III) oxide.