Dielectric properties of ga-doped Na0.5K0.5NbO3

In this Article, we investigated the dielectric properties of B-site Ga-doped K_0.5Na_0.5NbO3 (KNN) in air using AC impedance spectroscopy from room temperature to about 800 *C. Powder X-ray diffraction (PXRD) studies showed the formation of perovskite-type structure with orthorhombic symmetry, √2a_p × 4a _p×√2a_p (where a_p is perovskite-type lattice constant) for x ) 0.01, 0.1, and 0.13 members of Na0.5K0.5Nb1-xGaxO3. The PXRD result is similar to the parent KNN structure. AC impedance results showed mainly bulk contribution over the frequency range of 0.1 Hz to 1 MHz for the x ) 0.01 member, while bulk and grain-boundary contributions were present for x > 0.01 in the same frequency range. Scanning electron microscopy was used to study the effect of microstructure change for Ga³⁺ substitution in KNN. The inclusion of Ga3+ in KNN showed a significant change in the microstructure. The dielectric properties of Na0.5K0.5Nb1-xGaxO3 were enhanced by increasing the Ga³⁺ content; among the compounds studied, the x ) 0.1 member exhibited the highest dielectric constant and lowest dielectric loss at 1 MHz over the temperature range studied. All of the Na _0.5K_0.5Nb_1-xGa_xO₃ materials had a maximum dielectric constant at around 420 *C, which is consistent with other KNN ceramics reported in the literature and can be attributed to the Curie temperature. A small peak in the dielectric constant at around 220 *C was due to a structural phase transition.