Doping mechanisms and dielectric properties of Ca-doped bismuth magnesium niobate pyrochlores

Here we report the doping mechanisms and dielectric properties of Ca-doped bismuth magnesium niobate (BMCN) pyrochlores synthesised using solid-state reaction at 1025 degrees C over 24-48 h. The extensive solid solution of (Bi3.36Mg0.64-xCax)(Mg1.28Nb2.72)O-13.76 (0 <= x <= 0.7) pyrochlores formed with a fully indexed cubic structure, space group Fd3m and lattice constants, a = b = c in the range 10.5621 (17)-10.5332 (14) angstrom. The SEM analysis confirmed that the surface morphologies of BMCN pyrochlores were of irregular polyhedral grains and their crystallite sizes, as calculated by Scherrer and Williamson-Hall methods, were found to be in the range 46-70 nm and 38-75 nm, respectively. These thermally stable BMCN pyrochlores were highly insulating materials that showed a reproducible dielectric behaviour over heat-cool cycles and their activation energies were estimated to be in the range 1.17-1.47 eV. High bulk dielectric constants, epsilon', 69-171 and low dielectric losses, tan delta, in the order of similar to 10(-3) were recorded at 30 degrees C and 1 MHz; negative temperature coefficient of capacitance (TCC) in the range, (-319)-(-933) ppm/degrees C was measured over similar to 30-300 degrees C at 1 MHz.