Losses and dispersion in ceramic piezocomposites

The multiphase ceramic composites are very complex objects for theoretical modelling and ultrasonic measurements. Changes in chemical composition on the phase interfaces as well as microporosity appearance during co-firing of composite components can alter elastic, electric and mechanical properties of composites. Spatial dispersion can distort ultrasonic pulse characteristics and make ultrasonic measurements ambiguous. Therefore, a comprehensive study of different piezocomposite structures (porous piezoceramics, composites ceramics/ceramics and ceramics/crystals) including computer 3D simulation, impedance spectroscopy and ultrasonic measurements were carried out in this paper. Wave 3000 Pro computer software package based on finite differences method was used for full time domain solution of the 3D visco-elastic wave equations. The 3D composites objects for simulation were generated both internally using Wave3000 Pro ??Geometry?? routines and externally from optical and SEM slice data for real composites elements. Complex sets of elastic, dielectric, and piezoelectric parameters of the ceramic piezocomposites were determined by ultrasonic and impedance spectroscopy methods using Piezoelectric Resonance Analysis (PRAP) software. The simulation results were compared with the experimental data. Microstructural and physical mechanisms of elastic, piezoelectric and dielectric losses and spatial dispersion in ceramic piezocomposites were considered. Anomalies of sound velocities and attenuation near corresponding elastic percolation thresholds were found out.