We report the crystal structure together with the electric field gradient (EFG) tensor at the Hf site in Sr 0 . 5 Ba 0 . 5 HfO 3 as a function of temperature. High-temperature X-ray diffraction data show a second-order tetragonal-to-cubic phase transition at 700K. The hyperfine interaction measured at 1 8 1 Ta probe corresponds to a static, asymmetric and disordered EFG. The hyperfine parameters V z z and η also display evident changes close to 673K confirming the phase transition observed by XRD. The line width of the quadrupole interaction is relatively small compared with other perovskite-type compounds.