Fundamental structure-property relationships towards engineering of an integrated NP0 capacitor for bismuth pyrochlore systems

A comprehensive investigation of the processing-structure-property-performance (PSPP) interrelationship in the Bi2O3-ZnO-Nb2O 5 (BZN) pyrochlore system towards engineering of an integrated NP0 capacitor with silver electrodes for LTCC (low temperature cofire ceramics) microwave applications is presented. Using the BZN system as a model several specific areas or research are investigated and then correlated to obtain a global understanding of the PSPP interrelationship governing Bi-based pyrochlores.; The first area of investigation covers the phase formation for the cubic pyrochlore with nominal composition Bi3/2ZnNb3/2O 7 and monoclinic zirconolite Bi2Zn2/3Nb4/3 O7 compounds through XRD (X-ray diffraction) phase analysis. Formation reactions sequences are identified. In both phases, BNbO4 is found to be a precursor reacting primarily with ZnO. It is also found that in order to kinetically limit the residual BiNbO4, the calcination and sintering profiles should spend limited time at temperatures between 650°C and 750°C. It is shown that high ZnO activity is essential for the phase formation process and therefore the process is extremely dependent on milling and mixing. In addition, alternative processing routes are studied to ensure phase purity. Batching with excess ZnO and low pO2 processing atmospheres are demonstrated as successful options to reduce residual BiNbO4. The solubility of the main BZN phases to ZnO is investigated revealing a wide compositional windows resulting in single phase ceramic. These results serve as a guide for the appropriate modifications in batching and processing required to obtain a BZN composite ceramic exhibiting desirable NP0 characteristics (temperature coefficient of capacitance (TCC) ∼15 ppm/°C, mean dielectric constant of 96 and dielectric loss ∼0.001 at 1 MHz), which can be densified at 950°C with no sintering additives.; The second area covers the phase refinement of the main phases in the Bi2O3ZnO-Nb2O5 pyrochlore system performed via detailed XRD, Neutron Diffraction (ND) and Transmission Electron Microscopy (TEM). Essential and unique features in this phase are revealed by ND analysis like the sheet like structure based on HTB- (hexagonal tungsten bronze) like layers formed by [Nb(Zn)O6] octahedra and stacked along the c-axis. (Abstract shortened by UMI.)...