Effects of Bi2O3 impurities in ceramic ZnO on photoacoustic spectra and current-voltage characteristics

Photoacoustic (PA) spectroscopy is applied to study the optical absorption of ceramic ZnO doped with 1 mol% Bi2O3 sintered at various temperatures (700-1100 degrees 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 facto: (slope of exponential optical absorption) 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 at region B increases rapidly as the sintering temperature increases, indicating an occurrence of structural ordering by the Bi2O3 liquid phase sintering effect. The varistor effect (highly nonohmic behavior in the current-voltage characteristics) of ceramic ZnO doped with 1 mol% Bi2O3 is correlated with the characterization obtained by the PA method.