Subsolidus solution and electrical properties of Sr-substituted bismuth magnesium niobate pyrochlores

Here we investigated the structural and dielectric properties of (Bi3.36Mg0.64-xSrx)(Mg1.28Nb2.72)O-13.76 (0 <= x <= 0.5) subsolidus solution. Sr-substituted bismuth magnesium niobate (BMSN) pyrochlores were prepared by solid-state reaction at 1025 degrees C over 1-2 days. X-ray diffraction (XRD) analysis confirmed that the BMSN pyrochlores crystallise in cubic symmetry, space group Fd3m with lattice parameters in the range 10.5968 (4)-10.5671 (17) angstrom. The surface morphologies of these samples, as confirmed by Scanning Electron Microscopy (SEM), were composed of irregular shaped grains. Both Scherrer and Williamson-Hall methods revealed that the crystallite sizes were in the range 46-75 nm. No thermal event was discernible over the temperature range 30-1000 degrees C, thus confirming the thermal stability of these materials. On the other hand, Arrhenius conductivity plots showed the BMSN pyrochlores to be highly insulating with activation energies of similar to 1.20-1.49 eV. At similar to 30 degrees C and 1 MHz, BMSN pyrochlores exhibited moderate high bulk dielectric constants, epsilon', 90-186 and low dielectric losses, tan 6 in the order of 10(-2)-10(-1), respectively. Both the e' and tan 5 values of the BMSN pyrochlores showed a nearly two-fold decrease with increasing Sr concentration. Negative temperature coefficient of capacitances, TCC, -408 to -713 ppm/degrees C were recorded over similar to 30-300 degrees C at 1 MHz.