Synthesis, Thermal, and Electrical Properties of Bi2NiNb2O9 with Pyrochlore Structure

Nickel-containing cubic pyrochlore Bi2NiNb2O9 (space group $$Fd\bar {3}m$$ , a = 10.53657(6) Å) was synthesized by the citrate method. At the synthesis temperature of 1050°C, low-porosity ceramics with unclear grain boundary outlines are formed. The disordered structure of pyrochlore (space group $$Fd\bar {3}m$$ , a = 10.53784 Å, Z = 4) was refined by the Rietveld method based on X-ray powder diffraction data. The studied pyrochlore belongs to isotropically expanding oxide compounds with an average value of the thermal expansion coefficient of (6.4 × 10–6)°C–1 in the range of 30–750°C. Above 1110°C, thermal dissociation of Bi2NiNb2O9 occurs with the formation of the impurity phase NiNb2O6. Bi2NiNb2O9 is characterized by a high activation energy of 1.43 eV and a frequency- and temperature-independent permittivity of 144 (up to 300°C), low dielectric losses of ∼0.002 at 1 MHz. The studied ceramics can be used as a high-frequency dielectric material in the creation of multilayer ceramic capacitors.