NONSTOICHIOMETRY EFFECTS AND THEIR ADDITIVITY ON ANOMALOUS PHOTOVOLTAIC EFFICIENCY IN LEAD LANTHANUM ZIRCONATE-TITANATE CERAMICS

(Pb0.97La0.03)(Zr-0.52, Ti-0.48)(1-0.03/4)O-3 ceramics doped with various amounts of Ta were sintered at 1200 degrees C for 2 h and then heat-treated in nitrogen at 900 degrees C for 1 h to investigate the nonstoichiometric effects on the anomalous photovoltaic effect (APE). In the samples pretreated in nitrogen, both the photovoltaic current and the photovoltage were increased by the doping of Ta, and showed maxima around 1.5 mol% of doped Ta. Similar photovoitaic change with various amounts of Ta was observed in the nitrogen-treated samples. They, however, showed markedly higher values of the photovoltaic current and voltage than those in the doped samples pretreated in nitrogen. From this result, additivity is confirmed to hold for the effect of Ta doping and that of nitrogen treatment on the APE, indicating the coexistence of two types of contributions to the APE through different mechanisms. The spectral responses showed peak shifts and curve extension of the photovoltaic current to different directions according to the two effects. The mechanisms of those effects were discussed.