Electrical properties of BN-B4C and BN-SiC composites

The electrical properties and their relationship to the microstructures of BN-B₄C and BN-SiC composites are being studied. These materials were processed by hot pressing and are highly anisotropic due to the platelet nature of graphitic BN. The electrical properties of samples with volume fractions ranging from pure BN to pure B₄C or SiC have been measured. The resistivity and impedance spectra of these materials are highly dependent not only on the volume fraction of the constituent phases, but on the orientation of the electric field in which the measurement was made with respect to the BN platelets. The microstructures of these composites have been studied using SEM and TEM. X-ray diffraction has been used to determine the degree of texturing in the samples due to preferred orientation of the BN platelets during hot pressing. Correlations between the microstructure and the electrical properties will be discussed. Modeling of the data has been performed using the McLachlan equation, a combination of effective media theory and percolation theory. Three independent parameters are used to fit this equation-two exponential terms and a critical volume fraction. Conclusions about the fitted model parameters and their relationship to the microstructure are also given