Effect of magnesium content on structure and dielectric properties of cubic bismuth magnesium niobate pyrochlores

Structure and dielectric properties of cubic pyrochlore Bi1.5MgNNb2.5−NO8.5−1.5N (BMN) compositions with N=0.6–1.3 have been studied. X-ray diffraction (XRD), infrared reflectivity spectra and Raman spectra were employed to analyze the crystal structures and phonon vibration modes of BMN compositions. The vibration spectra were sensitive to the content of Mg2+ ions, which is caused by the randomness of Mg2+ ions partially filling both the cubic pyrochlore A and B sites. The intensity of A3O stretching vibrations became stronger with increasing Mg2+ content, but B3O stretching vibrations were quite opposite. With the increase of Mg2+ content, the dielectric constant and loss tangent both increased. Temperature dependent dielectric constant was observed in the samples with N>0.8. The tendency of the dielectric constant with the increasing temperature showed a quick drop in the samples with higher Mg2+ content, which seems to be associated with the disorder in the A2O′ network.