Dielectric properties of Ba3−xKxCaNb2O9−δ (0.5 < x < 1.25) (KBCN) double perovskites

We report synthesis, structure and dielectric properties of double perovskite-type Ba3−xKxCaNb2O9−δ (x = 0.5, 0.75, 1, 1.25) (KBCN). Powder X-ray diffraction (XRD) confirmed the formation of double perovskite-type structure and lattice constant decreases with increasing K in KBCN. AC impedance study showed a single semicircle over the investigated temperatures and frequencies in dry H2, H2 + 3% H2O, 3% H2O + N2, while two semicircles were observed at low temperatures in air, which could be attributed to bulk and grain-boundary contributions. Unlike un-doped BCN, KBCN exhibits negligible grain-boundary and electrode effects to the total electrical properties and is consistent with perovskite-type K-doped BaZrO3. The bulk dielectric constant and dielectric loss were found to increase with increasing K content in KBCN and also found to change with sintering temperature. Among the samples investigated, Ba1.75K1.25CaNb2O9−δ sintered at 1100 °C showed the highest dielectric constant of 65 at 106 Hz and dielectric loss of 0.14 at 400 °C in air. Isothermal dielectric constant and electrical conductivity at 1 MHz were found to be independent at elevated temperatures, while vary at low-frequency and low temperatures. Below 700 °C, dielectric constant and dielectric loss decreases with increasing frequency, whereas an opposite trend was observed for the electrical conductivity.

Electrical conductivity, dielectric constant and dielectric loss of Ba1.75K1.25CaNb2O9−δ in air at 400–700 °C.Figure optionsDownload as PowerPoint slideResearch highlights
► We show the effectiveness of AC impedance spectroscopy to screen dielectric materials and to understand contributing effects on the dielectric properties of polycrystalline metal oxides.
► Unlike Ba3CaNb2O9, Ba3−xKxCaNb2O9−δ exhibits negligible grain-boundary and electrode effects to the total electrical properties and is consistent with perovskite-type K-doped BaZrO3.
► Among the samples investigated, Ba1.75K1.25CaNb2O9−δ sintered at 1100 °C showed the highest dielectric constant of 65 at 106 Hz and dielectric loss of 0.14 at 400 °C in air.