Dielectric Properties of Ga-Doped Na0.5K0.5NbO3

In this Article, we investigated the dielectric properties of B-site Ga-doped K0.5Na0.5NbO3 (KNN) in air using AC impedance spectroscopy from room temperature to about 800 degrees C. Powder X-ray diffraction (PXRD) studies showed the formation of perovskite-type structure with orthorhombic symmetry, root 2a(p) x 4a(p) x root 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 I MHz over the temperature range studied. All of the Na0.5K0.5Nb1-xGaxO3 materials had a maximum dielectric constant at around 420 degrees 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 degrees C was due to a structural phase transition.