The effect of repeated sol infiltrations on the microstructure and electrical properties of PZT composite sol-gel films

PZT films in excess of 20 mum thick can readily be fabricated by repeated deposition of a powder/sol-gel slurry. The resultant films often contain a considerable level of porosity which has a detrimental effect on the material properties. A technique for increasing the density of such films through the use of controlled heat treatments and sol infiltration is presented. It is shown that with increased levels of sol infiltration the density and the relative permittivity of the films is increased. Measurements of the piezoelectric properties indicate that sol infiltration can lead to an increase in d(33) and e(31,f) . A sample with approximately 10% closed porosity was obtained following 4 infiltration steps per layer. This resulted in a maximum relative permittivity of approximately 80% of the quoted bulk value. Using a poling condition of 5mins at 200degreesC a maximum value d(33) of 70p C/N was obtained. Examination of cross-sections of the films produced shows that for intermediate levels of sol infiltration (typically between 1 and 3) a density gradient is obtained with higher densities observed nearer to the base of the film. It is postulated that the observed density gradient is a result of continued infiltration from the upper layers when further layers of slurry are deposited. The effects of changing the number of infiltration steps upon the film structures and electrical properties will be discussed.