Characterization of transparent polyimide:PLZT (8/65/35) composite films prepared by a modified sol-gel method

Abstract

PLZT (8/65/35) sol was prepared by the metal alkoxide route with methoxyethanol as solvent and acetic acid as catalyst. PLZT:Polyimide composite films were obtained by in-situ polymerisation of polyimide and gelation of sol. Composite films with optical transmittivity in excess of 70 % in the visible range were obtained on Corning 7059 glass and quartz substrates by the solvent cast technique and densified at 400°C. We report X-Ray diffraction studies which establish the crystallinity of the PLZT phase and results of IR spectroscopy which confirm the existence of imide linkages in the polyimide after densification of the composite film at 400°C. The variations of dielectric constant with frequency and with temperature are reported. Clear evidence of Curie temperature transition could not be observed in these specimens. The room temperature dielectric constant of 20 μm thick composite film at 1 kHz is found to be ≈ 13 and the loss tangent about 0.01. Hysteresis studies have demonstrated the high breakdown strength of the composite though no saturation has been observed in the polarisation. These films may find several applications in optical waveguides, display devices and spatial light modulators.