Dielectric and thermal expansion studies have been carried out in the relaxer ferroelectric system of PFN1-x-PZN(x). These compositions show two distinct regions of thermal expansion behaviour from room temperature to 800 K. As the T-c of the system increases, the lower expansion region extends. At higher values of x (>0.7), the pyrochlore phase appears, resulting in higher values of alpha. Addition of BaTio(3) suppresses the pyrochlore phase and reduces the magnitude of alpha in the relaxer region. The width of the low expansion region is also reduced due to the lowering of T-c in these compositions.