Photoacoustic spectra and current-voltage characteristics of ceramic ZnO doped with Bi2O3 impurities

Photoacoustic (PA) spectroscopy is applied to study the optical absorption of ceramic ZnO doped with 1 mol%Bi2O3 sintered at various temperature (700-1100 deg. C). PA signal intensities plotted semilogarithmically reveal two individual regions below 3.0 eV (A:3.0-2.7 eV; B:2.6-2.4 eV). The steepness factor obtained at region A decreases as the sintering temperature increases, indicating an increase of Bi2O3 segregation at particle surfaces and grain boundaries which might contribute to the interface states. The steepness factor B increases rapidly as the sintering temperature increases, indicating an occurrence of structural ordering by the Bi2O3 liquid phase sintering effect. The varistor effect of these samples is correlated with the characterization obtained by PA method