Structures and solid solution mechanisms of pyrochlore phases in the systems Bi2O3–ZnO–(Nb, Ta)2O5

Abstract

a b s t r a c tThe crystal structures of two pyrochlore phases have been determined by Rietveld refinement of combined X-ray and neutron powder diffraction data. These are stoichiometric, Bi 1.5 ZnTa 1.5 O 7 and nonstoichiometric Bi 1.56 Zn 0.92 Nb 1.44 O 6.86 . In both structures, Zn is distributed over A-and B-sites; Bi and Zn are displaced off-centre, to different 96g A-site positions; of the three sets of oxygen positions, O(1) are full, O(2) contain vacancies and O(3) contain a small number of oxygen, again in both cases. Comparisons between these structures, those of related Sb analogues and literature reports are made.Crown

Effect of Sn4+ and W6+ substitution on the dielectric properties of Bi2O3–ZnO–Nb2O5-based low firing ceramics

“…In this Bi 2 O 3 -ZnO-Nb 2 O 5 pyrochlores, NbO 6 and ZnO 6 octahedra with shared vertices form a three-dimensional network resulting in large cavities which contain the O 0 and A site atoms in an A 2 O 0 tetrahedral net [14]. It has considerable compositional and structural flexibility, including the possibility to incorporate a wide range of dopant ions [15][16][17]. Thus ion substitution, such as Mg 2?…”

Structures, phase transformations, and dielectric properties of (1−x)Bi2Zn2/3Nb4/3O7–xBi1.5NiNb1.5O7 pyrochlore ceramics prepared by aqueous sol–gel method

“…It has considerable compositional and structural flexibility, including the possibility to incorporate a wide range of dopant ions [11][12][13][14]. Thus ion substitution, such as Cu 2+ , Mg 2+ , Sr 2+ , Ce 4+ , Zr 4+ and Ti 4+ [15,16], is normally used to improve the dielectric properties, especially to enhance dielectric constant and adjust temperature coefficient of dielectric constant.…”