Photoelectrochemical effect on YBa/sub 2/Cu/sub 3/O/sub 7/ single crystals

Electrochemical dc and transient measurements in the system YBa/sub 2/Cu/sub 3/O/sub 7// acetonitrile + tetrabutylammonium-perchlorate (as a supporting electrolyte) at T = 298 K showed a significant photoeffect on single crystal electrodes after irradiation with chopped white or monochromatic light under cathodic polarization conditions. The effect could not be observed on polycrystalline electrodes and on single crystals under anodic polarization conditions. Under potentiostatic control, the photoreduction current increased nearly exponentially with decreasing electrode potential. Obviously, an enhanced reduction of copper oxide components at the surface takes place during illumination. The photoeffect was found to depend on both the photon energy and the adjustment of the (twinned) single crystals and may be explained assuming a significant band gap in c-direction and an intrinsic photo-excitation of electrons from the valence band to the conduction band of the p-type conducting material.