Comparison of microwave dielectric behavior between Bi1.5Zn0.92Nb1.5O6.92 and Bi1.5ZnNb1.5O7

The microwave dielectric, Bi1.5ZnNb1.5O7 exhibits low-temperature dielectric relaxation. To find the origin of the dielectric relaxation of Bi1.5ZnNb1.5O7, we studied the structure and dielectric behavior of Bi1.5ZnNb1.5O7 in detail. The Bi1.5ZnNb1.5O7 is not composed of a single phase pyrochlore structure. Instead, it consists of unusual structure of Bi1.5Zn0.92Nb1.5O6.92 and ZnO. The ZnO is distributed evenly in the grain and at the boundary of the Bi1.5Zn0.92Nb1.5O6.92 structure. Many small voids (<1 μm) were observed in the samples due to the loss of volatile Bi during sintering. The Bi1.5Zn0.92Nb1.5O6.92 exhibited a broad dielectric relaxation between 100 and 400 K at 1.8 GHz, peaking around 230 K. The Fourier transformation IR spectra predict that dielectric relaxation may occur near room temperature during extremely high frequencies (THz). The substitutional point defects in Bi1.5Zn0.92Nb1.5O6.92 provide room for dielectric relaxation at microwave frequencies. The low quality factor Q × f (∼520 GHz) of Bi1.5Zn0.92Nb1.5O6.92 results from both the dielectric relaxation of the material and the voids within its microstructure. The presence of ZnO phase in the Bi1.5ZnNb1.5O7 produces interstitial defects that further enhance the dielectric relaxation with reduced quality factor Q × f (∼426 GHz).