Comparison of microwave dielectric behavior between Bi_1.5 Zn_0.92Nb_1.5O_6.92 and Bi_1.5 ZnNb_1.5O₇

The microwave dielectric, Bi_1.5ZnNb_1.5O₇ exhibits low-temperature dielectric relaxation. To find the origin of the dielectric relaxation of Bi_1.5ZnNb_1.5 O₇, we studied the structure and dielectric behavior of Bi_1.5ZnNb_1.5O₇ in detail. The Bi_1.5ZnNb_1.5O₇ is not composed of a single phase pyrochlore structure. Instead, it consists of unusual structure of Bi_1.5Zn_0.92Nb_1.5 O_6.92 and ZnO. The ZnO is distributed evenly in the grain and at the boundary of the Bi_1.5Zn_0.92Nb_1.5 O_6.92 structure. Many small voids (<1 μm) were observed in the samples due to the loss of volatile Bi during sintering. The Bi_1.5Zn_0.92Nb_1.5O_6.92 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 Bi_1.5Zn_0.92Nb_1.5O_6.92 provide room for dielectric relaxation at microwave frequencies. The low quality factor Q × f (∼520 GHz) of Bi_1.5 Zn_0.92Nb_1.5O_6.92 results from both the dielectric relaxation of the material and the voids within its microstructure. The presence of ZnO phase in the Bi_1.5 ZnNb_1.5O₇ produces interstitial defects that further enhance the dielectric relaxation with reduced quality factor Q × f (∼426 GHz).