Disordered Structures and Dielectric Properties of Ni-Doped Bismuth Magnesium Niobate Pyrochlores

Bismuth based cubic pyrochlores are attractive candidates for microwave agile devices. The structure dependence of dielectric properties of Bi1.5Mg1–x Ni x Nb1.5O7 (Ni-BMN, x = 0.0–0.5) ceramics are discussed systematically. All the Ni-BMN pyrochlores show a cubic pyrochlore structure with a preferential (222)-orientation. However, Ni2+ ions entering would reduce the symmetry of cubic pyrochlore structure, which may increase the disorder degree of cubic pyrochlore structure. The detailed status of A2O and BO6 networks in Ni-BMN are revealed by structure analysis. The dielectric constant of Ni-BMN pyrochlores show slightly decrease from 168 to 148 with increasing Ni-doping content due to the lower polarizability of Ni2+. However, Ni-doping can effectively decrease the dielectric loss of Ni-BMN pyrochlores from 0.00072 to 0.00039. Moreover, Ni-doping improves the temperature stability of Ni-BMN pyrochlores, which is attributed to the altered O–Ni-O chain.