Pyrochlore pellets with the Gd(2)(Ti(2-x)Zr(x))O(7) stoichiometry (x = 0, 1 and 2) were irradiated with swift heavy ions in order to investigate the effects of electronic excitation and to determine the electronic stopping power threshold for track formation. XRD results showed that the electronic excitation induced by 870 MeV Xe and 780 MeV Kr ions leads to: (i) a crystalline-amorphous transition for Gd(2)Ti(2)O(7) and Gd(2)TiZrO(7), (ii) a phase transition towards an anion-deficient fluorite structure (order-disorder transition) for Gd(2)Zr(2)O(7). Thus, zirconate pyrochlores present a better radiation resistance under swift heavy ion irradiation than titanate pyrochlores. Moreover results underline the existence of an electronic stopping power threshold around 13-14 keV/nm, below which phase transformations do not occur. (C) 2010 Elsevier B.V. All rights reserved.