Photovoltaic and photostrictive effects in lanthanum-modified lead zirconate titanate ceramics.

摘要

Photostriction is the light induced strain in a material, arising from the combination of photovoltaic and converse-piezoelectric effects. The possibility of directly producing strain by light illumination, without any electrical lead wire connection, makes the photostrictive materials very attractive for potential usage in future generation wireless remote controlled micro-actuator and micro-sensor. However, for the fabrication of these devices, materials exhibiting higher photovoltaic effect and higher response speed must be developed.; This research was aimed towards investigating the mechanism of photovoltaic effect, developing photostrictive materials with enhanced performance, and exploring the limits of the photostriction.; A new model based on the optical nonlinearity in ferroelectrics having noncentric symmetry has been proposed to explain the mechanism of photovoltaic effect. This model provides a better understanding of photostrictive phenomenon and agrees well with the experimental measurements carried out on PLZT ceramics.; Among the various processing routes attempted, coprecipitation route was found to be most suitable for the fabrication of PLZT ceramics. High purity homogeneous powders with stoichiometric compositions obtained from this method yielded compacts with high density, fine grain size and uniformly distributed dopants. These desirable properties resulted in enhancement of photostrictive response. Photovoltaic and photoinduced strain were found to increase with decreasing grain size and increasing relative density.; The composition, especially near the morphotropic phase boundary (MPB) of PLZT ceramics, was optimized for photovoltaic characteristics. The maximum photocurrent was observed in tetragonal phase 4/48/52 PLZT, while the maximum photovoltage was observed in 5/54/46 PLZT, which is around the MPB of the PLZT phase diagram.; The photostriction was found to be strongly influenced by the surface characteristics (namely, sample thickness and surface roughness) of the sample. Enhancement in photovoltaic and photostrictive effects were observed with decrease in the surface roughness and sample thickness. Theoretical models have been formulated to explain these experimental observations. The model---correlating the sample thickness to photostrictive effect---provides a tool to optimize the sample thickness, which is an important parameter in designing of thick film bimorphs for enhanced efficiency micromechanical devices.