All-ceramic lead-free percolative composite with a colossal dielectric response

All-ceramic lead-free percolative composite, comprising RuO2 with high electrical conductivity denoted as the conductive phase and ferroelectric (K, Na)NbO3 ceramics, was developed. Structural analysis revealed a uniform distribution of conductive ceramic grains within the ceramic matrix. Consequently, the dielectric response in the (K, Na)NbO3–RuO2 composite follows the predictions of the percolation theory. Thus, close to the percolation point exceptionally high values of the dielectric constant were obtained—values as high as 20,000 were detected at room temperature at 1 kHz. Fit of the data, obtained for samples of different compositions, revealed critical exponent and percolation point, which reasonably agree with the theoretically predicted values.