Phase transitions in lead hafnate (PbHfO3) at high temperature and high pressure were studied by single-crystal diffraction and diffuse scattering of synchrotron radiation, using heated diamond anvil cell. Measurements were carried out in the temperature range 182 ° С <T <316 ° C and the pressure range 1.6 GPa <P <2.6 GPa. Four areas, characterized by different patterns of diffraction, have been identified on temperature increase, corresponding to antiferroelectric phase, a set of modulated phases, and two phases with distortions of the oxygen sublattice. In the lower-temperature phase of the latter two, a temperature-dependent diffuse scattering maximum is observed. It corresponds to a non-zero wave vector, and indicates the possible nature of the transition to the modulated phase as a transition due to condensation of an incommensurate soft mode.