Doping mechanisms and impedance study of Ba-substituted bismuth magnesium niobate pyrochlores

摘要

Here we investigated the doping mechanisms and electrical properties of Ba-substituted Bi3.36Mg1.92-xBaxNb2.72O14.36 (BMBN) pyrochlores. Phase-pure BMBN pyrochlores prepared by solid-state reaction were found to crystallise in a cubic structure (Fd3m; No. 227) with their lattice parameters in the range 10.5968(16) - 10.5879(3) angstrom. The Scanning Electron Microscopy (SEM) analysis revealed that BMBN pyrochlores were composed of irregular shaped grains and their estimated crystallite sizes by both Williamson-Hall and Scherrer methods were in the range 50-75 nm and 60-70 nm, respectively. Neither thermal event nor significant weight loss was observed over the studied temperature range similar to 30-1000 degrees C, confirming that BMBN pyrochlores were thermally stable with negligible Bi2O3 loss. The high activation energies in the range 1.18-1.30 eV, as determined by the Arrhenius conductivity plots, showed BMBN pyrochlores to be highly insulating. The dielectric constants, epsilon' and dielectric losses, tan delta were found in the range 147-183 and 7.9 x 10(-2) - 9.6 x 10(-2) at similar to 30 degrees C and 1 MHz. Negative temperature coefficient of capacitances, TCC, in the range (-478) - (-688) ppm/degrees C were recorded over similar to 30-300 degrees C at 1 MHz.