Compositions in the solid solution series {Pb(Fe0.5Nb0.5)O-3}(1-x) - {PbTiO3}(x) (x = 0 --> 1) were prepared by solid state reaction. The phase transition from rhombohedral/tetragonal to cubic structure has been studied as a function of x by differential thermal analysis, high temperature x-ray diffraction and dilatometry in the temperature range 298-773K. Dielectric measurements and thermal expansion coefficients of the x = 0.2 composition indicate that the relaxor type behaviour of lead iron niobate is extended up to 453K.