Enhanced tunable characteristics of the Na/sub 0.5/Bi/sub 0.5/TiO/sub 3/-NaTaO/sub 3/relaxor-type system

We have investigated the voltage-tunable characteristics of the Na_0.5Bi_0.5TiO₃-NaTaO₃ homogeneity region, for which samples were prepared using a conventional solid-state reaction. The highest value of the relative tunability (n_r) was obtained for the sample with 5 mol% of NaTaO₃, i.e., 47% at 1 MHz and a 70 kV/cm dc bias field. This sample also showed the highest value of the dielectric losses (tan delta) and temperature coefficient of the dielectric constant (tau_epsiv), i.e., 0.05 and 4478 ppm/K, respectively. As the concentration of NaTaO₃ increased up to 90 mol% n_r, tan delta, and tau_epsiv gradually decreased toward 22%, 0.0002 and -899 ppm/K, respectively. The dielectric constant of the samples varied in a similar manner between 662 and 130. At microwave frequencies, the dielectric losses of the samples substantially increased due to their relaxor-type nature. The lowest value was obtained for the samples with 90 mol% of NaTaO₃, i.e., 0.002. The tunable characteristics of the samples are related to the ferroelectric and dielectric properties, and it appears that the dielectric tunability of the Na_0.5Bi_0.5TiO₃-NaTaO₃ system originates from its relaxor-type behavior.