Phase Formation of Co and Cr Co-Doped Bismuth Niobate with Pyrochlore Structure

The formation mechanisms of pyrochlore-type Bi2Co1/2Cr1/2Nb2O9+Δ (space group Fd-3m, a = 10.4838(8) Å), in the temperature range from 400 to 1050 °C were studied by employing X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. An extensive reaction between binary metal oxides was found begin at temperatures above 550 °C, following transition monoclinic α-Bi2O3 into tetragonal β-Bi2O3 polymorph. synthesis process occurs several stages when Bi-rich intermediate products (Bi6CrO12, Bi6Cr2O15, Bi5Nb3O15) transform bismuth-depleted BiNbO4 chromium–cobalt spinel is formed. single pyrochlore phase final stage via doping bismuth ortho-niobate, BiNbO4, cations. observed mechanism essentially similar tantalate-based phases except for Bi5Nb3O15 stages.