This paper describes the evolution of a sol-gel-derived PbZrxTi1-xO3 film microstructure and ferroelectricity as a function of thickness in the 0.2-1.2 mu m range. In particular, we concentrate on the pyrochlore (Py) content in the film studied by the quantitative analysis of HRSEM images and corresponding ferroelectric properties. We have found that the Py content decreases with increasing thickness and have explained this phenomenon by a different extent of lead loss during processing. The ferroelectric hysteresis and fatigue of the films are correlated with the Py content. This paper shows that the Py presence in the film is responsible for the thickness-dependence of the coercive field.